Immune Responses Regulated by Cannabidiol
Department of Basic Sciences, Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi.
Barbara L.F. Kaplan
Department of Basic Sciences, Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi.
Department of Basic Sciences, Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi.
* Address correspondence to: Barbara L.F. Kaplan, Department of Basic Sciences, Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, 240 Wise Center Drive, Mississippi State, MS 39762 [email protected]
This Open Access article is distributed under the terms of the Creative Commons Attribution Noncommercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are cited.
Introduction: Cannabidiol (CBD) as Epidiolex ® (GW Pharmaceuticals) was recently approved by the U.S. Food and Drug Administration (FDA) to treat rare forms of epilepsy in patients 2 years of age and older. Together with the increased societal acceptance of recreational cannabis and CBD oil for putative medical use in many states, the exposure to CBD is increasing, even though all of its biological effects are not understood. Once such example is the ability of CBD to be anti-inflammatory and immune suppressive, so the purpose of this review is to summarize effects and mechanisms of CBD in the immune system. It includes a consideration of reports identifying receptors through which CBD acts, since the “CBD receptor,” if a single one exists, has not been definitively identified for the myriad immune system effects. The review then provides a summary of in vivo and in vitro effects in the immune system, in autoimmune models, with a focus on experimental autoimmune encephalomyelitis, and ends with identification of knowledge gaps.
Conclusion: Overall, the data overwhelmingly support the notion that CBD is immune suppressive and that the mechanisms involve direct suppression of activation of various immune cell types, induction of apoptosis, and promotion of regulatory cells, which, in turn, control other immune cell targets.
Cannabidiol History and Therapeutic Uses
Cannabidiol (CBD) is a plant-derived cannabinoid that has structural similarity to the primary psychotropic congener in cannabis, Δ 9 -tetrahydrocannabinol (THC). While CBD was initially isolated in the 1940s, its structure was not elucidated until the 1960s. 1,2 Unlike THC, CBD is bicyclic, comprised a terpene and an aromatic ring, and is a pentyl side chain. 1 It exists as two enantiomers, and it is (−)CBD 3 that is one of the major constituents found in Cannabis sp., and will be the focus of this review. For many years, THC and CBD were designated as psychoactive and nonpsychoactive, respectively, owing to the fact that THC produces the euphoric high associated with cannabis use, while CBD does not. However, since we know that CBD produces biological effects in the central nervous system (CNS), perhaps it is better defined as psychoactive, but not psychotropic, since it is active in the CNS without producing the euphoric high.
Perhaps it was the association of the euphoric high with THC that provided the initial focus on THC as opposed to CBD for potential medical use, since THC was originally identified as the active component of the plant. 4 However, in recent years, researchers have begun to explore CBD more as a therapeutic addition or alternative to THC. In the United States, oral THC (dronabinol, Marinol ® ) was first approved in 1985 by the Food and Drug Administration (FDA) to treat nausea and vomiting associated with chemotherapy. In 1992, dronabinol was also approved to treat cachexia in AIDS patients. 5 The next major advancement in cannabinoid pharmaceuticals was not until the mid-2000s when Sativex ® (nabiximols), a combination of THC and CBD as an oromucosal spray, was approved in Canada and the EU for neuropathic pain in multiple sclerosis (MS) and intractable cancer pain. 6 There are several reasons why combining THC and CBD in a single therapeutic could have value. 6 First, additional therapeutic benefit might be gained from hitting multiple targets; for example, if THC alleviates pain and CBD alleviates anxiety, 7–16 the combination therapy could be quite effective for chronic pain sufferers. Second, for disease states in which both THC and CBD are efficacious, a combination might allow for lower doses of THC, thereby potentially decreasing the psychotropic effects of THC. Third, there are some studies suggesting pharmacokinetic interactions between CBD and THC in which CBD treatment increases THC levels, 17–20 thereby allowing longer duration of effects of THC. Sativex ® has been evaluated in several clinical trials for spasticity associated with MS, neuropathic pain, and other conditions. 21–37
The latest approved cannabinoid pharmaceutical in the United States is CBD as Epidiolex ® . It was approved by the U.S. FDA in 2018 for epilepsy in children, in particular, for Dravet Syndrome and Lennox-Gastaut Syndrome. 38–42 CBD is also being investigated for its effectiveness in other diseases, including Tuberous Sclerosis, a genetic condition that causes growth of benign tumors all over the body, 43,44 schizophrenia, 45 and refractory epileptic encephalopathy. 46
In addition to the federally approved uses of CBD as Epidolex ® , CBD, usually as CBD oil, is widely used for putative medical benefit in several states, and is certainly used in states in which cannabis has been decriminalized, or legalized, for recreational use. 47 There are reports that CBD and other cannabinoids are beneficial for sleep, anxiety, pain, post-traumatic stress disorder, schizophrenia, neurodegenerative disorders, and immune-mediated diseases. 48 Often these conditions are self-diagnosed and self-treated, so there can be issues with dosing, other drug interactions, and characterization of CBD safety and efficacy.
Overall, it is clear that exposures to CBD are increasing. 47,49–51 It is also clear that CBD possesses therapeutic benefit, and in some cases, the beneficial effects of CBD are for diseases for which other available treatments have not been efficacious. 52 Together, these observations demonstrate the critical need to continue research on CBD, and therefore the goal of this review is to provide a summary of the effects and mechanisms by which CBD alters immune function. The review will include an evaluation of the role for various receptors through which CBD acts in the immune system. There will also be a description of CBD effects in animal and human immune responses, a characterization of mechanisms by which CBD mediates immune effects, and identification of knowledge gaps regarding CBD’s actions in the immune system.
Identification of CBD Receptors and Other Targets
Upon identification of the cannabinoid receptors, CBD was determined to exhibit low affinity for CB1 53 and CB2 receptors. 54 Consistent with this, we showed CBD-induced suppression of cytokine production in mouse splenocytes in both wild-type and double cannabinoid receptor knockout mice (Cnr1 −/− /Cnr2 −/− mice). 55 Another study demonstrated that ophthalmic administration of CBD following corneal inflammation reduced neutrophils in both wild-type and CB2 receptor knockout mice. 56 CBD-mediated suppression of anti-CD3-mediated proliferation of T cells also occurred in both wild-type and CB2 receptor knockout splenocytes. 57 However, there are a few reports using inflammatory stimuli in which CBD’s actions have been attributed to either CB1 or CB2 receptors ( Table 1 ). In a sepsis model induced with bacterial lipopolysaccharide (LPS), CBD-mediated inhibition of gastric emptying was reversed with the CB1 receptor antagonist, AM251. 58 Similarly, CBD inhibited interleukin (IL)-1 in a hypoxia-ischemia brain insult model and this effect was reversed with the CB2 receptor antagonist, AM630. 59 Use of ovalbumin to induce an asthma-like disease in mice demonstrated that some cytokines and chemokines induced in the lungs of mice that were suppressed by CBD (IL-4, IL-5, IL-13, and eotaxin) were differentially regulated by CB receptors. 60 Specifically, CBD-induced suppression of IL-5 was reversed in the presence of the CB2 receptor antagonist in bronchoalveolar lavage fluid and lung tissue, but there was no clear receptor dependence identified for CBD’s suppression of IL-4, IL-13, or eotaxin. 60 Thus, several studies do suggest a possible role for cannabinoid receptors in CBD-mediated suppression of inflammatory effects. It should also be noted that there are several reports suggesting that CBD acts as an allosteric modulator of CB1 or CB2 receptors, 61–64 although the role for CB1 or CB2 receptor allosteric modulation by CBD in immune function has not yet been determined.
Receptors Identified in Mediating Cannabidiol Immune Effects
FAAH, fatty acid amide hydrolase; PPAR-γ, peroxisome proliferator-activated receptor gamma; TRPV1, transient receptor potential vanilloid 1.
Another mechanism by which CBD acts is through inhibition of fatty acid amide hydrolase (FAAH), 65–67 suggesting that some of CBD’s effects are mediated by anandamide elevation since FAAH is responsible for the breakdown of anandamide. 65,66 Anandamide is an endogenous cannabinoid that exhibits affinity for CB1 and CB2 receptors. 68,69 A recent study suggested that the mechanism by which CBD elevates anandamide involves CBD interaction with fatty acid binding proteins, which prevents anandamide binding to these proteins to block anandamide transport to FAAH. 67 Since anandamide exhibits affinity for CB1 and CB2 receptors, and oxidation products of anandamide through cyclooxygenase or cytochrome P450 enzymes produce metabolites that also exhibit affinity for CB1 and CB2 receptors, 70,71 anandamide or its metabolites could account for some of the reports that CBD acts through CB1 and/or CB2 receptors. 58,61–64,72–84
Actions of CBD in immune function might also be mediated by the transient receptor potential V1, known as the vanilloid receptor (TRPV1), which was found to be activated by CBD. 65 Specifically, CBD was found to increase intracellular calcium in HEK cells transfected with TRPV1, and the CBD-induced increase in calcium was blocked by the TRPV1 antagonist, capsazepine. 65,66 Follow-up studies demonstrated that CBD desensitizes TRPV1 following activation. 85 Other studies have suggested that CBD acts through TRPV1 in the immune system ( Table 1 ). CBD can induce myeloid-derived suppressor cells (MDSCs), a type of regulatory cell, in the liver, and this effect is lost in TRPV1 knockout mice. 86 Specifically, regarding inflammation, CBD attenuated thermal hyperalgesia in response to carrageenan injections or in a neuropathic pain model in a capsazepine-dependent manner. 87,88 CBD suppression of cytokines in inflamed primary human colonic tissue was attenuated by the TRPV1 antagonist, SB366791. 82 SB366791 was also effective in reversing CBD’s suppression of rolling and adherent leukocytes in the sodium monoiodoacetate model of osteoarthritis in rats. 83 Together, these data suggest that TRPV1 is a critical receptor through which CBD acts in the immune system.
There have been several critical articles in which adenosine A2A receptors have been shown to mediate CBD’s effects in the immune system. 89–91 CBD was shown to inhibit microglial cell proliferation, which was associated with inhibition of adenosine uptake into cells. 89 The studies also demonstrated that CBD suppression of tumor necrosis factor-alpha (TNF-α) could be reversed using an adenosine A2A receptor antagonist, and CBD-induced suppression of LPS-stimulated TNF-α was not observed in adenosine A2A receptor knockout mice. 89 The role for adenosine A2A receptor in CBD-mediated neuroprotection or suppression of neuroinflammation was demonstrated in a model of hypoxia-ischemia in newborn mouse brains. 90 CBD inhibited adenosine uptake into rat microglial cells and CBD enhanced adenosine’s ability to inhibit TNF-α, which was prevented by the adenosine A2A receptor antagonist, ZM241385. 91 These studies show that CBD acts through the adenosine A2A receptor, especially in microglial cells.
CBD’s effects have also been shown to be mediated by peroxisome proliferator-activated receptor gamma (PPAR-γ) using PPAR-γ antagonists in models of β amyloid neuroinflammation, 92 apoptosis, 93,94 dinitrobenzene sulfonic acid (DNBS)-induced colitis, 95 human ulcerative colitis, 96 LPS activation of microglial cells, 97 and hypoxia-ischemia model of neuroinflammation. 98
There are several reports that CBD acts through the serotonin 5-HT1a receptor ( Table 1 ). Although most of the evidence for the involvement of this receptor comes from the attenuation of CBD’s effects using the 5-HT1a antagonist, WAY100635, early studies demonstrated that CBD displaced binding of the 5-HT1a agonist, 8-OH-DPAT, in membranes from CHO cells expressing the human 5-HT1a receptor. 99 Few of the CBD-mediated effects acting through the serotonin 5-HT1a receptor have been reported in immune cells, but immune cells do express 5-HT1a. 100–103 One study showed that IL-1 produced in the brain in response to hypoxia-ischemia insult was inhibited by CBD, and reversed with the 5-HT1a receptor antagonist, WAY100635. 59
Studies have suggested that CBD might act through other receptors, including other TRP receptors, 66,85,104–107 or opioid receptors. 108 There is also evidence that CBD acts through blockade of GPR55, 109 and specifically that CBD modestly antagonized proinflammatory effects in human innate cells following GPR55 activation. 110 Thus, together, the current data support that immune effects of CBD are mediated through activation of CB1, CB2, TRPV1, adenosine A2A, and PPAR-γ receptors, blockade of GPR55 receptors, and FAAH inhibition.
CBD Immune System Effects and Mechanisms
Immunity is maintained through various cell types acting together to provide protection against foreign invaders, and simultaneously avoid reactions against self-proteins. Thus, an appropriate immune response requires a regulated balance between robust reactions against non-self, but limited or no reactions against self. Cell types include neutrophils, macrophages, and other myeloid cells comprising the innate immune system, which reacts quickly to destroy pathogens. In the event that an innate response is insufficient, certain innate cells can activate the adaptive immune response, comprised predominantly of T and B cells. T cells can then provide signals that recruit and activate other immune cells, or directly lyse or induce apoptosis of infected cells. T cells can also help stimulate B cells, which produce antibodies to neutralize pathogens and/or enhance destruction of the pathogens. Communication between the various cell types, and therefore the innate and adaptive immune responses, is mediated by expressed or secreted proteins called cytokines or chemokines. Inflammation is the process commonly associated with the innate immune response since pathogen destruction can also cause tissue damage, although T cells certainly are proinflammatory as well. In fact, many cell types, regardless of whether they are immune cells, produce proinflammatory cytokines in response to inflammation.
The effects of CBD on immune responses can involve innate or adaptive responses. In assessing these responses, various cell types and their functions have been examined. For instance, a common end-point to examine regardless of cell type is cytokine or chemokine production. Typical proinflammatory cytokines include IL-1α, IL-1β, IL-6, TNF-α and IL-17A, while IL-10 is considered anti-inflammatory. Some cytokines are produced by specific T cell subsets; for instance, the Th1 subset produces interferon-gamma (IFN-γ) and promotes cell-mediated cytotoxicity, while the Th2 subset produces IL-4 and promotes B cell responses. Other end-points that might provide clues of disruption of immune competence are nitric oxide or myeloperoxidase (MPO) production from innate cells, as these are often released during pathogen destruction. Thus, the effects of CBD on immune function are presented by cell type, outlining known mechanisms by which CBD alters various end-points. Tables 2–4 include the studies described in the text (and others) and are organized by experimental approach. As indicated above, inflammation can induce proinflammatory cytokine production in nonimmune cells, so there are also a few of those examples included in the tables.
Cannabidiol-Induced Immune Suppression by Cell Type in Human Cells In Vitro
|Human cell lines b||↓cytokines||186|
|Jurkat and MOLT-4 T cells b||↑apoptosis||80a|
|Human coronary artery endothelial cells||↓adhesion molecules, migration, transcription factors, nitrative stress||119a|
|Jurkat T cells b||↓cytokines, transcription factors||55a|
|THP-1 cells b||↓IDO||142|
|Human intestine||↓proteins and nitric oxide||96|
|Human liver sinusoidal endothelial cells||↓adhesion molecules||118|
|Human gingival mesenchymal stem cells||↓inflammatory genes||79|
|Caco-2 cells b||↓phosphoproteins||82a|
|Primary colonic explants||↓cytokines||82a|
|Human PBMCs||↓proliferation and cytokines||146a|
|HaCaT human keratinocytes b||↓cytokines||84|
|Human plasmacytoid dendritic cells||↓CD83 expression in HIV + dendritic cells||134a|
ROS, reactive oxygen species.
Cannabidiol-Induced Immune Suppression by Animal Cell Type In Vitro
|B6C3F1 female splenocytes||↓IL-2||196|
|EL-4 T cells a||↑apoptosis||80b|
|Mouse EOC-20 microglial cells a||↓proliferation||89b|
|BALB/c male splenocytes||↓IL-4 and IFN-γ||140b|
|B6C3F1 female splenocytes||↓IL-2 and IFN-γ||55b|
|BALB/c male thymocytes and EL-4 T cells a||↑apoptosis||150b|
|BALB/c male splenocytes||↑apoptosis||151b|
|Sprague-Dawley rat microglial cells c||↓adenosine uptake,||91b|
|BV-2 cells a||↓cytokines, ↓NF-κB activation||147b|
|Mouse brain slices c||↓cytokines||90b|
|Rat male astroglial cells||↓gliosis||92b|
|C57BL/6 male Kupffer cells||↓TNF-α||118|
|BALB/c microglial cells c||↑apoptosis||156b|
|BV-2 cells a||↓oxidative stress, ↓Ccl2||159|
|MOG-specific female T cells||↓IL-17A and IL-6||144b|
|Mouse brain endothelial cells a||↓VCAM-1 and leukocyte adhesion||164b|
|Rat astrocytes c||↓Ccl2||164b|
|RAW cells a||↓TNF-α||148|
|MOG-specific female T cells||↓cytokines||143b|
|Rat male splenocytes and mesenteric lymph nodes||↓proliferation and cytokines||146b|
|Primary mouse male and female microglial cells||↓activation||97b|
|BV-2 cells a||Alteration of circadian rhythm-associated genes||197|
|BV-2 cells a||alteration of miRNAs||161b|
|C57BL/6 or BALB/c female splenocytes||↓proliferation and cytokines||57|
c Sex not stated for cells derived from animals (or in the case of primary microglial cell isolates, not determined in newborn animals).
IFN-γ, interferon-gamma; IL, interleukin; miRNA, microRNA; MOG, myelin oligodendrocyte glycoprotein; NF-κB, nuclear factor-κB; TNF-α, tumor necrosis factor-alpha; VCAM-1, vascular cell adhesion molecule-1.
Cannabidiol-Induced Immune Suppression in Animals In Vivo
|Model||Disease model||Route, dose range, and duration/frequency a||Major effects||Reference|
|Male CD-1 mice||sRBC||i.p.||Modest ↓antibody production||155|
|Male DBA/2 mice||Collagen-induced arthritis||i.p. or oral||↓disease, ↓TNF-α and IFN-γ||139b|
|2.5–20 mg/kg for i.p.|
|5–50 mg/kg for oral|
|Male ICR mice||Carrageenan-induced inflammation||ethosome (CBD in ethosomal gel)||↓inflammation||198|
|100 mg of ethosomal CBD (3%)|
|Male Wistar rats||Carrageenan-induced inflammation||Oral||↓disease, ↓prostaglandin (PGE2)||199|
|Female NOD mice||Diabetes||i.p.||↓disease incidence, ↓IL-12, TNF-α and IFN-γ, ↑IL-4||123|
|Female C57BL/6 mice||EL-4 leukemia growth||i.p.||↑apoptosis of tumor cells||80b|
|12.5 or 25 mg/kg once|
|Male Wistar rats||Sciatic nerve pain or CFA-induced inflammation||Oral||↓pain, ↓TNF-α, ↓prostaglandin (PGE2)||88|
|Male Sprague-Dawley rats||Ischemia-reperfusion injury (myocardial)||i.p.||Modest ↓infarct size, ↓TNF-α||200|
|C57BL/6J mice c||Aβ inflammation||i.p.||↓IL-1β, ↓iNOS||117|
|2.5 or 10 mg/kg|
|Male BALB/c mice||Ovalbumin (asthma)||i.p.||↓serum antibodies, ↓IL-2, IL-4, and IFN-γ||140b|
|Male ddY mice||Focal cerebral ischemia||i.p.||↓infarct size, ↓neutrophil MPO activity||129b|
|various times surrounding occlusion|
|Female NOD mice||Diabetes||i.p.||↓disease incidence, ↓IL-6 and IL-12, ↑IL-4 and IL-10||124b|
|5 injections per week for 4 weeks|
|Female B6C3F1 mice||sRBC||Oral||Modest ↓antibody production||55b|
|Male ICR mice||DNBS colitis||i.p.||↓inflammation, ↓colon weight:length ratio, ↓iNOS, IL-1β, ↑IL-10||95b|
|Male Wistar rats||None||i.p.||↓blood leukocytes and lymphocytes, ↓B, T and CTL cells, ↑NK and NKT cells||201|
|2.5 or 5 mg/kg|
|Male CD-1 mice||Diabetes||i.p. or i.n.||↓diabetic pain, ↓density of microglial cells||81b|
|0.1–2 mg/kg i.n.|
|1–20 mg/kg i.p.|
|Male C57BL/6 mice||Streptozotocin-induced diabetes||i.p.||↓disease, ↓TNF-α, NF-κB activity, ICAM-1, VCAM-1, iNOS, p-p38, p-JNK, ↑p-AKT||120b|
|Male Wistar rats||TNBS colitis||i.p.||Modest ↓disease, ↓colonic contractions, ↓neutrophil MPO activity||130|
|Male Wistar rats||Cecal ligation and puncture||i.p.||↑disease survival||184|
|once or up to 9 days|
|Female Sabra mice||Hepatic encephalopathy (bile duct ligation)||i.p.||Improved disease-associated cognitive impairments, ↓TNF-α||202|
|Male BALB/c mice||Ovalbumin (footpad)||i.p.||↓footpad swelling, ↓TNF-α and IFN-γ, ↑IL-10||188|
|Male Swiss OFI mice||LPS i.p.||i.p.||↓mast cell infiltration, macrophage activation marker, ↓TNF-α||96|
|Female C57BL/6 mice||Experimental autoimmune hepatitis||i.p.||↓hepatic inflammation, ↓IL-2, TNF-α, IFN-γ, IL-6, IL-17A, IL-12, MCP-1 (CCL-2), and eotaxin, ↑MDSCs||86b|
|Male C57BL/6 mice||Ischemia reperfusion injury (liver)||i.p.||↓hepatic inflammation, ↓MIP-1α, ICAM, MIP-2, TNF-α, NF-κB activity, ICAM-1, iNOS, p-p38, p-JNK||118|
|3 or 10 mg/kg|
|C57BL/6 mice c||LPS i.v.||i.v.||↓vasodilation, leukocyte margination, and extravasation, ↓COX-2, TNF-α, and iNOS||121|
|1 or 3 mg/kg|
|Male C57BL/6 mice||LPS-induced pulmonary inflammation||i.p.||↓BALF lymphocytes, macrophages, and neutrophils, ↓TNF-α, IL-6, MCP-1 (CCL-2), and MIP-2||125b|
|Male Wistar rats||Meningitis (Streptococcus pneumoniae)||i.p.||Improved disease-associated cognitive impairments, ↓TNF-α||203|
|once or up to 9 days|
|C57BL/6 mice c||Cerulein (pancreatitis)||i.p.||↓disease, ↓TNF-α and IL-6, ↓neutrophil MPO||128b|
|Newborn pigs c||Hypoxia-ischemic brain injury||i.v.||neuroprotection, ↓IL-1||59b|
|Male Wistar rats||Ovalbumin (asthma)||i.p.||↓TNF-α, IL-6, IL-4, IL-5, and IL-13||127b|
|Male C57BL/6 mice||LPS-induced pulmonary inflammation||i.p.||↓inflammation, ↓BALF lymphocytes, macrophages, and neutrophils, ↓TNF-α, IL-6, MCP-1 (CCL-2), and MIP-2||132|
|Female C57BL/6 mice||None||i.p.||↑MDSCs||136b|
|Female C57BL/6 mice||Malaria (Plasmodium berghei)||i.p.||↓IL-6 and TNF-α||204|
|Male Sprague Dawley rats||Freund’s Adjuvant (osteoarthritis)||Transdermal||↓inflammation, ↓TNF-α||205|
|Male ICR mice||DNBS Colitis||i.p. or oral d||↓colon weight:length ratio, ↓neutrophil MPO||131|
|5–30 mg/kg for i.p. 10–60 mg/kg oral|
|Female NOD mice||Type 1 diabetes||i.p.||↓disease||206|
|5 injections/week for 10 weeks|
|Male A/J mice||Experimental autoimmune myocarditis||i.p.||↓disease, ↓lymphocyte populations in heart, ↓IL-6, IFN-γ, IL-1β, and MCP-1 (CCL-2)||126b|
|Male Wistar rats||Middle cerebral artery occlusion||i.c.v.||↓infarct size||149|
|Male Wistar rats||Middle cerebral artery occlusion||i.c.v.||↓infarct size, ↓TNF-α||207|
|Male Wistar rats||Sodium monoiodoacetate (osteoarthritis)||Intra-arterial||↓pain, ↓rolling and adherent leukocytes, ↓joint nerve demyelination||83b|
|Female C57BL/6 mice||Alcoholic liver disease||i.p.||↓liver damage, ↓neutrophils, ↓TNF-α, MIP-1, IFN-γ, IL-1β, and MCP-1 (CCL-2)||185|
|5 or 10 mg/kg|
|Male and female dogs||Osteoarthritis||Oral e||↓pain||208|
|2 and 8 mg/kg|
|every 12 h for 4 weeks|
|Male Wistar rats||Ulcerative tongue lesion||i.p.||↓inflammation||209|
|5 or 10 mg/kg|
|3 or 7 days|
|Female C57BL/6 mice||Spinal cord contusion||i.p.||↓spinal cord CD4 T cells, ↓IL-23A, IL-23R, IFN-γ, CXCL9, CLCL11, NOS2, and IL-10||189|
|1 and 24 h after injury, on day 3, then twice/week up to 10 weeks|
|Male Sprague-Dawley rats||Carrageenan-induced inflammation||Oral||↓hyperalgesia||210|
|100 or 10,000 μg/kg|
|Male Swiss mice||Haloperidol-induced inflammation||i.p||↓IL-1β and TNF-α, ↑IL-10||97b|
|twice/day up to 21 days|
|Male BALB/c mice||Corneal inflammation||Topical (ophthalmic)||↓pain, ↓neutrophils||56b|
|3% or 5%|
|Male ICR mice||Ischemia-reperfusion injury (kidney)||i.p.||↓kidney injury, ↓TH17 cells, ↑Tregs and Treg17 cells||152b|
|Female C57BL/6 and BALB/c mice||Syngeneic or allogeneic bone marrow transplant||i.p.||↓lymphocyte recovery||57|
|every other day for 2 weeks|
|BALB/c mice||Ovalbumin (asthma)||i.p.||↓airway resistance; ↓IL-4, IL-5, IL-13, and eotaxin||60b|
|5 or 10 mg/kg|
|three times at time of ovalbumin challenge|
CBD, Cannabidiol; DNBS, dinitrobenzene sulfonic acid; iNOS, inducible nitric oxide synthase; i.n. intranasal; i.p., intraperitoneal; JNK, c-jun N-terminal kinase; LPS, lipopolysaccharide; MDSCs, myeloid-derived suppressor cells; MPO, myeloperoxidase; sRBC, sheep red blood cell; TNBS, 2,4,6-trinitrobenzene sulfonic acid; Treg, regulatory T cell.
CBD effects and mechanisms of immune suppression in innate cells
One of earliest effects reported with CBD was in human mononuclear cells, 111,112 in which TNF-α, IFN-γ, and IL-1α were all suppressed (0.01–20 μg/mL CBD or 0.03–64 μM CBD). Later studies focused on human monocytic cells revealed that CBD can induce apoptosis in either HL-60 (1–8 μg/mL CBD or 3.2–26 μM CBD) 113 or primary human monocytic cells (1–16 μM CBD). 114,115 Macrophages are also targets, although they have been studied more commonly in animal models. Peritoneal macrophages were used early on to demonstrate that CBD (3 μg/mL or 10 μM) targets nitric oxide, 116 and this has also been a well-studied target of suppression by CBD in many tissues and cell types. The mechanism by which CBD suppressed nitric oxide involves suppression of endothelial 87 or inducible nitric oxide synthase (iNOS) 58,95,117–121 in response to various inflammatory stimuli. iNOS is known to be regulated by the transcription factor nuclear factor-κB (NF-κB), 122 which is comprised of p65 and other proteins, and becomes active after degradation of the inhibitory protein, IκB. Decreased expression of iNOS by CBD correlated with stimulation of the inhibitory IκBα protein and inhibition of NF-κB p65 protein expression. 119,120 Using peritoneal macrophages from diabetic mice stimulated ex vivo with LPS revealed that macrophages isolated from CBD-treated mice did not produce as much TNF-α or IL-6 as macrophages isolated from vehicle-treated mice. 123,124 A direct effect of CBD decreasing macrophage numbers in the bronchoalveolar lavage fluid was shown following intranasal LPS administration to induce pulmonary inflammation. 125 There was also decreased expression of F4/80 (a marker of macrophages) mRNA expression by CBD in heart tissue in experimental autoimmune myocarditis. 126 Although this study identified CBD only affecting F4/80 mRNA expression as opposed to F4/80 cell surface staining, it does suggest a novel target (i.e., heart tissue) of CBD in a relatively understudied autoimmune model.
IL-6 is a proinflammatory cytokine produced by many cell types, predominantly innate cells. Many studies have shown that circulating IL-6 is readily inhibited by CBD in inflammatory models, including diabetes, 124 asthma, 127 pancreatitis, 128 and hepatitis. 86 CBD treatment in vivo resulted in lower IL-6 production in peritoneal macrophages stimulated ex vivo with LPS, 124 in the pancreas in acute pancreatitis, 128 and in bronchoalveolar lavage fluid in LPS-induced pulmonary inflammation. 125
There have been some reports that CBD alters neutrophil function. Compromised MPO activity by CBD has been studied in several tissues, including brain, 129 colon, 130,131 lung, 125,128,132 and pancreas. 128 Interestingly, in the pulmonary inflammation studies with LPS, neutrophil cell counts in the bronchoalveolar lavage fluid were also decreased by CBD compared to LPS. 125,132 Together, the results suggest that CBD’s mechanism for neutrophil suppression involves both decreased numbers of neutrophils and compromised MPO activity.
There are two recent studies focused on CpG stimulation of IFN-α production from human plasmacytoid dendritic cells. 133,134 While these studies are focused primarily on THC and other CB2 agonists, CBD was also used (1–10 μM) and did not affect IFN-α production. 133,134 It was interesting, however, that CBD suppressed the CD83 dendritic cell activation marker on dendritic cells derived from HIV + , but not healthy, individuals. 134 Reduction in dendritic cell CD83 signaling can compromise T cell function, 135 although additional studies using CBD in human dendritic cells and T cells are needed to establish the consequences of CBD-induced reduction in CD83 on HIV + dendritic cells.
Another mechanism by which CBD controls immune function is induction of regulatory cells. MDSC are innate, myeloid cells that possess the ability to control immune responses. Hegde et al. demonstrated that CBD induced CD11b + Gr-1 + MDSCs in the liver in a mouse hepatitis model. 86 Importantly, the isolated MDSCs were functional, that is, they suppressed proliferation of responder T cells ex vivo and improved liver function when administered before hepatitis induction. 86 CBD-induced MDSCs from the peritoneal cavity were able to attenuate inflammation in response to LPS. 136 In the experimental autoimmune encephalomyelitis (EAE) model, CBD induced MDSCs in the peritoneal cavity, but decreased the infiltration of MDSCs in the spinal cord and brain. 137 CBD-induced MDSCs from the peritoneal cavity were able to attenuate responder T cell proliferation ex vivo and attenuate EAE disease when administered in vivo. 137
CBD effects and mechanisms of immune suppression in lymphocytes
The area in which most of the effects of CBD in the immune system have been studied is T cells. Early studies examining rosette formation in response to sheep red blood cells (sRBCs) (generally considered to be a T cell response) revealed that CBD (1 and 100 μM) reduced this response. 138 Phytohemagglutinin (PHA)-stimulated IFN-γ production in T cells has also been shown to be inhibited by CBD (0.01–20 μg/mL or 0.03–64 μM). 111,112 Other studies have provided further evidence that T cell-produced IFN-γ is a critical target of CBD suppression. CBD inhibited IFN-γ production from lymph node cells isolated from arthritic mice stimulated ex vivo with collagen, 139 and from splenocytes isolated from NOD mice stimulated ex vivo with ConA. 123,124 IFN-γ production from splenocytes isolated from untreated mice was suppressed by CBD following ex vivo stimulation with phorbol 12-myristate 13-acetate/ionomycin (PMA/Io). 140 In the latter study, a 1-h exposure of CBD to the mice was meant to mimic the time for CBD distribution before receiving antigen sensitization with ovalbumin to induce asthma-like disease. 140 Thus, CBD’s ability to compromise various cytokines at the time of antigen sensitization might suggest that CBD affects primary activation of T cells, as has been suggested as part of the mechanism for other cannabinoids, such as THC. 141 Indeed, we have shown that a 30-min pre-treatment with CBD (0.1–20 μM) suppressed IFN-γ production in mouse splenocytes in response to PMA/Io or anti-CD3/CD28. 55 In these studies, it was shown that the mechanism by which CBD suppressed IFN-γ occurred at the level of transcription and that two important transcription factors for IFN-γ, activator protein-1 (AP-1) and nuclear factor of activated T cells (NFAT), were inhibited by CBD, suggesting a transcriptional mechanism for suppression. 55 CBD-induced suppression (0.1–10 μg/mL or 0.3–32 μM) of Ifng mRNA expression was shown using PHA-stimulated human PBMCs. 142 Given the many reports that IFN-γ seems to be a sensitive target of suppression by CBD, it was surprising that Ifng mRNA was not affected by CBD (5 μM) using encephalitogenic T cells stimulated by antigen-presenting cells (APCs) and myelin oligodendrocyte glycoprotein peptide (MOG35–55) in vitro. 143 However, CBD did inhibit expression of IFN-γ receptor 1 and CBD increased several IFN-γ-responsive genes known to attenuate T cell proliferation. 143 Overall, the data reveal that an important part of CBD’s action in the immune system is its ability to affect IFN-γ in multiple ways. Not only did CBD directly suppress IFN-γ production through a transcriptional mechanism under several conditions 55,142 but also suppressed IFN-γ receptor expression, and increased IFN-γ-induced genes that subsequently attenuate other immune targets. 143
A few other T cell-derived cytokines have been shown to be targets of CBD. As noted above, IL-6 is a critical target of CBD in many cells and tissues, 82,84,86,97,125–128,132 many of which are innate cells. However, IL-6 was also suppressed by CBD (5 μM) using encephalitogenic T cells stimulated by APCs and MOG35–55 in vitro, 144 and “IL-6 signaling” as a critical pathway suppressed by CBD. 143 Interestingly, “IL-17 signaling” was also identified as a critical pathway suppressed by CBD (5 μM) in T cells in vitro. 143 It should be noted that IL-6 promotes the differentiation of TH17 cells, 145 so the simultaneous suppression of IL-6 and IL-17A by CBD is consistent with CBD suppressing TH17 cell differentiation. Indeed, CBD (1–20 μg/mL or 3.2–64 μM) suppressed IL-17A production in human CD3 + T cells (derived from healthy patients or patients with MS or nonseminomatous germ cell tumors) stimulated ex vivo with PMA/Io. 146 Taken together with the data described in innate cells above, it is clear that CBD’s action in inflammation and immune function involves suppression of cytokine production from many different cell types.
The ability of CBD to suppress transcription factors such as NFAT, AP-1, and NF-κB likely accounts for its widespread suppression of many cytokines. 74,82,118–120,147–149 Some of the studies suggest that CBD increased, or perhaps stabilized, expression of IκB as part of the mechanism by which it suppresses NF-κB. 119,120,147 CBD (4 μM) stimulated IκB-α expression in high glucose-treated human coronary artery endothelial cells. 119 CBD induced expression of IκB-α in heart tissue from diabetic mice in vivo 120 and in LPS-stimulated microglial cells in vitro (CBD 1–10 μM). 147 It is interesting that NF-κB activity has not yet been identified as a target in T cells, suggesting that CBD-mediated suppression of NF-κB plays a bigger role in mediating anti-inflammatory effects in non-T cells.
Certainly, some of the dysregulation of these transcription factors is the result of suppression of various kinases upstream of their activation. Extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 MAPKs have all been identified as targets of suppression by CBD in various cell types. 74,80–82,118,120 Of these reports, one was conducted in human T cells. 80 In these studies, CBD (5 μM) was shown to suppress expression of total and phosphorylated p38 at the 16-h timepoint following CBD treatment. The authors also showed that the CBD-mediated inhibition of phosphorylated p38 was reversed by SR1445328 or tocopherol, suggesting that CBD acts through CB2 and that the mechanism of suppression involves reactive oxygen species (ROS) production. 80
Although well studied in cancer cell lines and primary tumor tissue, CBD-mediated apoptosis is also a contributor to the immune suppressive mechanism. Initially CBD-induced apoptosis in T cells was described in Jurkat and MOLT4 human T cells. 80 In the same study, McKallip et al. observed increased apoptosis of mouse lymphoma cells injected into, and then recovered from, the peritoneal cavity of mice that were treated with CBD. 80 Since then, there has been a series of studies characterizing the mechanisms by which CBD induced apoptosis in mouse immune cells. CBD (1–16 μM) was shown to induce apoptosis in mouse thymocytes and EL-4 T cells. 150 The same group demonstrated that CBD (1–16 μM) induced apoptosis in mouse splenocytes, including assessment of CBD-induced apoptosis by cell type (B220 + B cells and CD4 + and CD8 + T cells). 151 In both studies, CBD increased ROS, and CBD-mediated apoptosis was attenuated by N-acetylcysteine. 150,151 Wu et al. further demonstrated that the CBD increased ROS-activated caspase-8 to mediate apoptosis. 151 In follow-up studies in human monocytes, Wu et al. noted that CBD (1–16 μM) readily induced apoptosis, but that the effect of CBD on apoptosis was lost if the monocytes were pre-cultured for 72 h. 114 The authors suggest that the differential responsiveness to CBD was due to an increase in antioxidant capacity in cultured cells, which is a thought consistent with the mechanism by which CBD induced apoptosis in mouse lymphocytes. 150,151 CBD-induced apoptosis (1–16 μM CBD) in human monocytes was due to a cascade of intracellular events, including opening of the mitochondrial permeability transition pore, depolarization of the mitochondrial membrane potential, oxidation of a lipid in the mitochondrial inner membrane, and mitochondrial ROS generation, leading to cytochrome C release. 115 Thus, this latest study demonstrates a critical role of the mitochondria in CBD-induced apoptosis.
Another important mechanism by which CBD acts to control immune responses is through regulatory T cell (Treg) induction. In the ConA model of hepatitis, CBD modestly enhanced Tregs in the liver as quantified by CD4 + Foxp3 + cells. 86 A confirmation of in vivo induced Tregs by CBD was noted in an ischemia-reperfusion injury model in the kidney, in which CBD returned the disease-induced reduction in CD3 + Foxp3 + cells to baseline. 152 Interestingly, in the ischemia-reperfusion kidney model, CBD also induced “TReg17 cells,” which were defined as CD3 + Foxp3 + CCR6 + STAT3 + . 152 It has been suggested that Treg17 cells help control a TH17 response. In vitro, CBD (5 μM) induced a CD69 + LAG + population in CD4 + CD25 − cells, which were identified as one type of regulatory cell, and induced Il10 mRNA expression. 153 We showed in vitro that CBD (1–15 μM) induced functional CD4 + CD25 + Foxp3 + T cells under conditions of suboptimal stimulation and that Il10 mRNA expression was induced. 154
There are only a few studies in which B cells are identified as targets of CBD. CBD given at 25 mg/kg by intraperitoneal (i.p.) injection modestly reduced the sRBC-induced plaque-forming cells, which is a measure of antibody production. 155 We conducted a similar study using oral administration of CBD and also found modest inhibition of antibody production. 55 Other studies have shown that CBD robustly inhibited the sRBC-induced antibody production in vitro, 55 suppressed ovalbumin-induced IgM, IgG1, and IgG2a in an in vivo asthma model, 140 and reduced expression of activation markers such as major histocompatibility complex II, CD25, and CD69, on B cells. 153 CBD has also been shown to induce apoptosis in B cells. 151 Overall, the results suggest that B cells can be targets of suppression by CBD.
CBD-induced neuroprotection by suppression of microglial cell activation
There is no doubt that many of the mechanisms already identified for innate cells and lymphocytes also account for CBD’s ability to decrease microglial cell activation. CBD (1–16 μM) induced apoptosis in microglial cells, 156 which was dependent on activation of caspase 8 and 9, and was reversed in the presence of an agent that depletes cholesterol and disrupts lipid rafts. 156 These results suggest that CBD-induced apoptosis is dependent on lipid raft formation, 156 and indeed, this observation was confirmed by another group in BV-2 microglial cells. 157
BV-2 microglial cells have been used as a model in several articles, in which detailed transcriptional effects of CBD have been evaluated. 147,157–159 The mechanisms contributing to CBD (10 μM)-mediated suppression of LPS-stimulated cytokine production in microglial cells includes decreased activation of the Toll/IL-1 receptor domain-containing adapter-inducing IFN-β (TRIF)/IFN-β/signal transducer and activator of transcription (STAT) signaling pathway. 147 CBD suppressed LPS-stimulated NF-κB activation, and induced LPS-stimulated STAT3 activation, which has been shown to suppress NF-κB activation. 147 CBD (10 μM) was shown to affect several genes involved in lipid metabolism in unstimulated BV-2 cells, 157 which might account for CBD’s ability to increase anandamide 58,65–67,84,157,160 or could account for CBD’s dependence on lipid raft formation to induce apoptosis 156,157 Follow-up studies examining CBD’s effects in unstimulated BV-2 cells demonstrated that CBD (10 μM) alters zinc homeostasis, oxidative stress, and glutathione levels in microglial cells. 158,159 A recent study demonstrated that CBD alters microRNA (miRNA) expression, 161 and two of the CBD miRNA targets identified are discussed. First, CBD downregulated miR146-a, which acts as a negative regulator of inflammation, in both resting and LPS-stimulated cells, thereby contributing to CBD’s ability to downregulate proinflammatory cytokines. 161 Second, CBD upregulated miR-34a, which has several roles in cell survival, such as cell cycle, apoptosis, and differentiation. 161 These results show that CBD-induced alterations in miRNA expression are involved in the mechanism by which CBD suppresses immune function.
In vivo, CBD has been shown to decrease microglial accumulation in the spinal cord in diabetic mice, 81 which might contribute to attenuation of neuropathic pain, and CBD decreased haloperidol-induced activation of reactive microglial cells. 97 CBD’s suppression of TNF-α production from microglial cells in vitro was mediated by A2A adenosine receptors in EOC-20 mouse microglial cells (0.5–5 μm) 89 or rat retinal microglial cells (1 μM). 91
CBD Effects in Autoimmune Disease Models
EAE and MS
The immunosuppressive and neuroprotective mechanisms of CBD make it an ideal therapeutic candidate for MS, a neurodegenerative autoimmune disease of the CNS that affects ∼2.5 million people worldwide. The average age of onset is around 30 years, and symptoms can vary greatly for each patient based on the lesion locations within the CNS. 162 Two models frequently used in the laboratory environment to study MS are the EAE and Theiler’s murine encephalomyelitis virus (TMEV) models, and an increasing number of studies have shown promising results with CBD using these models ( Table 5 ). In 2011, Kozela et al. successfully demonstrated that CBD (5 mg/kg i.p.) administered at the onset of disease attenuated clinical disease, microglial activation, and T cell infiltration into the CNS in EAE, and that CBD reduced T cell proliferation in vitro. 163 CBD showed similar effects in the TMEV model, in which Mecha et al. demonstrated that CBD (5 mg/kg i.p.) administered for the first 10 days following disease onset reduced clinical disease and neuroinflammation by decreasing microglial activation and immune cell trafficking signals in the CNS. 164 Use of MOG35–55-specific T cells isolated from EAE mice in vitro has also been extremely vital to determining how CBD might be affecting T cells in these and other disease models. As outlined above, in the T cell section, in vitro CBD treatment of MOG35–55-specific T cells co-cultured with APCs with CBD suppressed IL-17A and IL-6 production, suggesting CBD suppressed TH17 development; however, production of Il10 mRNA was potentiated with CBD treatment, suggesting that CBD may have multiple suppressive mechanisms. 144 In vitro treatment of MOG35–55-specific T cells with CBD induced a Treg with a CD4 + CD25 − LAG3 + CD69 + phenotype, promoted upregulation of anergy-associated genes, such as Lag3, Erg2, and Il10, and altered the balance between STAT3 and STAT5 activation. 153 In another study, CBD administered during disease onset increased the number of functional MDSCs present within the peritoneal cavity, decreased neuroinflammation, and reduced IL-17A and IFN-γ in the serum. 137 When splenocytes from these mice were restimulated ex vivo, the CBD-treated mice had significantly decreased levels of IL-17A and IFN-γ, and increased levels of IL-10 in the supernatants. 137 Finally, a recent study using an adoptive transfer EAE model showed a reduction in neuroinflammation, demyelination, and axonal damage with CBD treatment during disease onset. 165 Adoptive transfer EAE is a variation of the EAE model induced by transfer of encephalitogenic T cells into naive mice, which allows experiments performed with this model to focus more on the T cell-specific mechanisms of pathogenesis in the EAE model. From the accumulation of data, it is obvious that multiple immune cell types, proinflammatory and anti-inflammatory, within the EAE model are modulated by CBD, but overall, CBD appears to downregulate proinflammatory pathways and upregulate anti-inflammatory pathways in the EAE model.
Cannabidiol Effects in Experimental Autoimmune Encephalomyelitis
|EAE in ABH||In vivo||In vivo: 0.5–25 mg/kg i.p.||No effects||211|
|EAE in C57BL/6||In vivo and in vitro||In vivo: 5 mg/kg i.p. in vitro: 1, 5, and 10 μM||in vivo: ↓disease severity, ↓T cell infiltration into the CNS, ↓microglial activation, ↓axonal damage in vitro: ↓T cell proliferation||163a|
|TMEV in SJL/J||In vivo and in vitro||In vivo: 5 mg/kg i.p. in vitro: 1 and 5 μM||in vivo:↓disease severity, ↓leukocyte infiltration into the CNS, ↓microglial activation, ↓CCL2 (MCP-1), ↓CCL5, ↓IL-1β ↓TNF-α in vitro: ↓sVCAM-1 production from endothelial cells, ↓leukocyte adhesion, ↓CCL2 (MCP-1)||164a|
|MOG35–55-specific T cells from EAE mice||In vitro||In vitro: 0.1, 1, and 5 μM||in vitro: ↓IL-17A, ↓IL-6, ↑IL-10||144a|
|MOG35–55-specific T cells from EAE mice||In vitro||In vitro: 5 μM||in vitro:↓IL-17A, ↓IL-6, ↑IL-10, ↑EGR2, ↑CD4 + CD25 − CD69 + LAG3 + phenotype, ↑STAT5/↓STAT3, ↓B cell activity, ↑Nfatc1, ↑Casp4, ↑Cdkn1a, ↑Icos, ↑Fas||153a|
|EAE in C57BL/6||In vivo||In vivo: 5 mg/kg i.p.||in vivo: ↓disease severity, ↓leukocyte invasion, ↓demyelination, ↓TNF-α, ↓IFN-γ, ↓IL-17A||212|
|EAE in C57BL/6||In vivo||In vivo: 10 mg/kg i.p.||in vivo: ↓disease severity, ↓FAS ligand, ↓ERK phosphorylation, ↓Caspase-3 activity, ↓Bax/↑Bcl-2, ↓p53-p21 activation, ↓apobody formation||166a|
|MOG35–55-specific T cells from EAE mice||In vitro||In vitro: 5 μM||in vitro: ↓IL-1β, ↓IL-3, ↓Xcl1 mRNA, ↓IL-12a mRNA, ↑Dusp6 mRNA, ↑Btla mRNA, ↑Lag3 mRNA, ↑Irf4 mRNA, ↑IL-10 mRNA||143a,b|
|EAE in C57BL/6||In vivo||In vivo: 10 mg/kg i.p.||in vivo: ↓disease severity, ↓leukocyte infiltration, ↑PI3k/Akt/mTOR phosphorylation, ↑S6k phosphorylation, ↑BDNF expression, ↑PPAR-γ, ↓IFN-γ, ↓IL-17A, ↓JNK activity, ↓p38 MAP kinase activity||167a|
|Adoptive Transfer EAE in C57BL/6||In vivo and in vitro||In vivo: 5–50 mg/kg i.p in vitro: 1, 5 & 10 μM||in vivo: ↓disease severity, ↓leukocyte invasion, ↓demyelination, ↓axonal damage, ↓microglial activation, ↓CB2 receptor expression in CNS, ↓GPR55 receptor expression in CNS in vitro: ↓Cell viability, ↓IL-6, ↑apoptosis, ↑ROS||165a|
|EAE in C57BL/6||In vivo||In vivo: 20 mg/kg i.p||in vivo: ↓disease severity, ↓leukocyte invasion, ↓IL-17A, ↓IFN-γ, ↓RORγT, ↓T-bet, ↑IL-10, ↑MDSC ex vivo: ↓IL-17A, ↓IFN-γ, ↑IL-10||137a|
CNS, central nervous system; EAE, experimental autoimmune encephalomyelitis; ERK, extracellular signal-regulated kinase; STAT, signal transducer and activator of transcription; TMEV, Theiler’s murine encephalomyelitis virus.
In addition to its immunomodulatory effects, CBD’s neuroprotective properties in the EAE model also indicate its therapeutic potential in MS. CBD has been shown to decrease the activation of proapoptotic proteins, such as caspase-3 and Bax, 166 and to counteract the effects of EAE on the PI3K/Akt/mTOR pathway, JNK, and p38 MAP kinases in the CNS of EAE mice. 167 Interestingly, the study from Giacoppo et al. found the PI3k/Akt/mTOR pathway was upregulated in neural tissues when EAE mice were treated with CBD. 167 However, Kozela et al. 153 observed a reduction in the activation of Akt in vitro in MOG35–55-reactive T cells, which might suggest a differential role for CBD’s effects on the PI3K/Akt/mTOR pathway in various cell types.
Despite the growing number of studies involving the neuroprotective and immunosuppressive effects of CBD, the majority of human studies involving cannabinoids and MS have been focused on the use of THC:CBD mixtures, with a particular focus on Sativex. Clinical studies that have been performed have shown that Sativex has beneficial effects on spasticity, mobility, bladder function, and pain in MS patients, and is well tolerated 22,25,28,31,168–175 ; however, there has been little focus on the neuroprotective and immunosuppressive effects of THC:CBD mixtures in MS, and so it is difficult to say at this point if the successful results observed with CBD in the animal models of MS will be observed in MS patients. For a more complete review on the effects of Sativex in MS, see Zettl et al. 176
Other autoimmune disease states
CBD has been shown to attenuate experimental autoimmune hepatitis, 86 experimental autoimmune myocarditis, 126 and autoimmune diabetes 123,124 in mice. There are few studies done with CBD only in human autoimmune diseases. In human patients, CBD at 20 mg/kg did not reduce clinical Crohn’s disease. 177 However, CBD is effective at attenuating intestinal inflammation in other models of human inflammatory bowel disease, 82,96 so it is possible that CBD could be effective at higher doses. Indeed, CBD as Epidolex for epilepsy in children is being used as high as 20 mg/kg, but CBD doses as high as 300 mg/kg have been evaluated, and have not exhibited significant adverse effects. 178
CBD Immune Enhancement Effects
Much of the data support the fact that CBD is immune suppressive and anti-inflammatory; however, there have been a few reports over the years that CBD has produced some immune enhancing effects ( Table 6 ). The potential for CBD, and other cannabinoids, to produce immune enhancing effects has been attributed to differences in hormetic (i.e., biphasic) responses depending on CBD concentration/dose, cell culture conditions, including serum presence and/or percent, immune stimulant, and magnitude of cellular activation in response to the immune stimulant. Indeed, studies from our laboratory and others have shown that CBD either enhanced or suppressed cytokine production (IL-2 and IFN-γ) in response to relatively low or high degree of immune stimulation, respectively. 154,179,180 The mechanism for the differential responsiveness likely involves alterations in intracellular calcium, as CBD increases intracellular calcium in mouse splenocytes regardless of the increase of intracellular calcium produced by the immune stimulant. 179 In addition, the differential cytokine production was correlated with nuclear expression of the NFAT transcription factor, 179 which is calcium responsive. Interestingly, CBD’s ability to increase intracellular calcium also likely accounts for some of the other enhancing effects, including stimulation of neutrophil degranulation, 181 chemotaxis, 182 and mast cell/basophil activation. 183
Carrier Oils for CBD: How to Choose the Best One
Adrienne Dellwo is an experienced journalist who was diagnosed with fibromyalgia and has written extensively on the topic.
Verywell Health articles are reviewed by board-certified physicians and healthcare professionals. These medical reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more.
Lana Butner, ND, LAc, is a board-certified naturopathic doctor and licensed acupuncturist in New York City.
If you’ve ever used a CBD oil, you’ve gotten more from the product than just cannabidiol (CBD). For multiple reasons, manufacturers include a carrier oil, too.
As its name suggests, a carrier oil delivers (or carries) the contents of the active compound. In this case, it’s CBD. In the realm of beauty products, carrier oils dilute essential oils because the essential oil may be too strong on its own. (For example, a lavender reaction from lavender oil can cause the skin to itch, burn, or break out in blisters.)
Carrier oils are important to CBD because they help dissolve the cannabinoid’s molecules so they can be absorbed by the body. Many carrier oils are similar, but they may have differences that could be important to you for various reasons. For example, most of them are nut-based or plant-based, and you could be allergic to them. Oils that are taken orally may not taste good to you. Reading the label is a smart move—as long as you know what you’re looking for.
This article explains the purpose of carrier oils and the possible side effects. It also describes the six carrier oils you’re likely to see in stores and online, including their advantages and drawbacks.
Marketing Outpaces Science
CBD is an abbreviation for cannabidiol. It’s one of 100-plus chemicals in the cannabis plant that may have health benefits. It’s widely assumed that CBD oil can relieve arthritis pain, chronic pain, and chronic nerve pain as well as reduce inflammation, ease anxiety, and improve sleep. Researchers are actively studying other uses for CBD oil, particularly in terms of slowing cancer cell growth.
Purpose of CBD Carrier Oils
CBD products use different carrier oils, sometimes alone and sometimes in combinations. They serve several important functions:
One key reason for using a carrier oil is that it improves bioavailability, which means it helps your body absorb CBD oil. CBD is fat-soluble, which means that it dissolves in oil rather than water. Fat-soluble substances are better absorbed when digested along with fat, even in small amounts.
When you digest water-soluble substances, like sugar or many vitamins and minerals, your digestive tract sends them directly into your bloodstream (because blood is a water-based liquid).
Fat-soluble substances can’t be absorbed this way. Instead, your digestive tract sends them into fatty tissues and they’re distributed through your body by the lymphatic system, which is part of your immune system. Any excess is stored in your liver and fatty tissues for later use.
All carrier oils are fat-soluble, which means CBD dissolves in it. Then the oil carries the CBD into the proper tissues so they’re more accessible by your body.
Know Your Tinctures
CBD products have introduced consumers to a new lexicon. For example, concentrated CBD oil usually taken through a dropper is known as a tincture.
CBD is a potent chemical, which means you don’t need much of it for a medicinal effect. However, this poses a problem when it comes to dosing. To deliver accurate and consistent doses, it’s easier to measure out a dropperful of CBD-infused oil than a tiny amount of crystalline isolate (which is CBD in pure form).
Added Health Benefits
Carrier oils sometimes include health benefits all on their own. For example, olive oil has gotten a lot of attention for its heart-healthy benefits.
If there’s an oil you’d like to get more of in your diet, adding it to your CBD regimen is one way to get it. (This said, it remains debatable whether one or two droppers of carrier oil a day is enough to have any tangible effect on your health. This is another CBD-related topic that falls under the category of “more research is required.”)
CBD Products Come From Hemp
CBD products almost always are derived from hemp, which is botanically and legally different from the marijuana plant. By law, CBD products can’t contain more than 0.3% THC (short for delta-9- tetrahydrocannabinol ), which is the chemical in marijuana that creates a high.
Side Effects and Precautions
Most people don’t have side effects from common carrier oils. Some oils, though, may not be right for people with certain illnesses or who take certain medications. Always check with your healthcare provider before adding anything to your dietary regimen—even a “natural” product like CBD in a carrier oil. Natural doesn’t always mean safe.
If you have tree-nut allergies or other food allergies, be especially diligent about selecting CBD products with carrier oils you know are safe for you. All ingredients should be specified on the label.
For topical preparations, know that some carrier oils or other added ingredients may cause an itchy, red rash called allergic contact dermatitis. Others may cause a skin reaction after sun exposure. Be sure you’re familiar with the potential side effects of whatever products you’re using. And play it safe by testing a miniscule amount of topical oil on an obscure patch of skin to see if you develop a reaction.
What About Essential Oils?
Carrier oils aren’t the same thing as essential oils used for aromatherapy. Essential oils are highly concentrated, which is why they have a strong fragrance. Many essential oils can cause poisoning when ingested or absorbed through the skin, even in small amounts. This is true even if the oil comes from something that is normally safe to ingest, such as nutmeg.
Essential oils are often used topically (on the skin) after being diluted by a carrier oil. Essential oils themselves, however, should never be used as a carrier oil. Some topical CBD formulations may include essential oils such as lavender or eucalyptus oils because of their purported health benefits.
Before using these products, be sure you’re familiar with the ingredients and that you’re not allergic to any of them. Watch also for side effects, which can occur soon after using them.
Common Carrier Oils
Some CBD oils may contain one or more carrier oils. Some common carrier oils are:
- Medium-chain triglyceride (MCT) oil
- Hemp seed oil
- Olive oil
- Avocado oil
MCT oil is the most common carrier oil for CBD products. It can be derived from coconut or palm kernel oil, but coconut is the most common source. On labels, it’s sometimes listed as fractionated coconut oil, which means it contains more liquid than solid compared to normal coconut oil, thanks to fatty acids.
Medium-chain triglycerides are a type of fatty acid that your body can quickly absorb because it doesn’t have to break it down via digestion before sending it off to the lymph system. It also absorbs easily through the skin.
Long-chain triglycerides require more digestion time. Short-chain triglycerides are often consumed by gut bacteria before they’ve had time to be absorbed. So MCTs are the most useful.
- Quick absorption due to molecular structure
- 90% saturated fat, which also aids absorption
- Light, thin oil
- Almost flavorless
- Doesn’t require chemical processing
- Less expensive than some carrier oils
- Slow to break down and go rancid
- Temporary digestive side effects (nausea, gas, diarrhea, vomiting) in some people
- Possible excessive build-up of ketones in the body (dangerous with poorly controlled diabetes)
- Not recommended for people with liver disease
- May interact with cholesterol-lowering statin drugs
Additional Health Claims
Some scientific evidence suggests that MCT oil may:
- Help with weight loss by reducing your appetite, increasing metabolism, and making your body burn calories faster
- Have benefits for people with autism, epilepsy, cancer, type 2 diabetes, and Alzheimer’s disease
- Activate the immune system to fight yeast and bacterial overgrowth
While promising, much of this research is preliminary. More research is needed before MCT oil can be recommended for these uses.
Scrutinize Coconut Oil Labels
If the label of a CBD product says “coconut oil,” it’s likely regular coconut oil and not MCT. While perfectly fine as a carrier oil, regular coconut oil may not have all of the same benefits of an MCT.
Hemp Seed Oil
It may come from the same plant, but hemp seed oil (sometimes called hemp oil) and CBD oil aren’t the same thing. CBD comes from the flower while hemp seed oil comes from the seeds. The seeds contain fewer beneficial chemicals (cannabinoids and terpenes) than the flower and in much lower concentrations. However, they do contain some hemp phytochemicals that aren’t present in the flowers.
Using hemp seed oil as a carrier oil for CBD may contribute to what’s called the “entourage effect,” which basically means that combining parts of the plant may make each component more effective than it would be alone.
This quality makes hemp seed oil a popular choice for “full-spectrum” products, which contain all of the component chemicals of the hemp plant rather than just CBD.
- Rich in omega-3 fatty acids, which may lower inflammation
- Ideal ratio of omega-3 to omega-6 fatty acids
- High antioxidant levels
- Good source of fiber
- Contains magnesium, calcium, iron, and zinc
- Possible entourage effect
- Lower solvency than MCT oil, meaning it can’t hold as much CBD
- Higher priced than MCT oil
- Flavor (sometimes described as “sharp” or “herby”) may clash with some palates
- Side effects may include diarrhea, nausea, throat irritation, slow heart rate, high blood pressure
Some companies try to pass off hemp seed oil as CBD oil. Be sure to check the ingredients and amount of CBD a product contains before you buy it. All reputable companies should provide this information on their labels and websites.
Additional Health Claims
Hemp seed has been used medicinally for a wide array of conditions, most of which have not been researched enough to say for sure whether they’re safe and effective. The conditions include:
, for its anti-inflammatory properties and blood pressure and other conditions involving skin inflammation
Olive oil is probably the carrier oil you’re most familiar with. It’s certainly the best researched. It’s become one of the most commonly used cooking oils because of its many well-established health benefits:
- High in iron, vitamin K, vitamin E
- Rich in antioxidants
- Highly trusted
- Absorbed by the skin even faster than MCT
- Its long-chain triglycerides are slower to absorb than MCT (but may absorb more efficiently)
- Lower solvency than MCT, meaning it can’t hold as much CBD
- Thicker than most other carrier oils, which may be unpleasant
- Flavor is relatively strong and may be distasteful to some people
Additional Health Claims
Thanks to a significant amount of research, olive oil is known to:
- Boost immunity
- Reduce inflammation
- Increase good cholesterol and lower bad cholesterol
- Prevent blood platelet clumping, which can cause heart attacks
- Aid in blood clotting
- Improve gut-bacteria balance
- Support proper nerve function
- Prevent cognitive decline
- Protect bones from thinning (osteoporosis)
Avocado oil has become more popular for a variety of uses, including cooking, as researchers have learned about its health benefits. As a CBD carrier oil, it’s used most often in topical products, but you can also find it in products that are meant to be ingested.
- Quickly and easily absorbed by your skin and digestive tract
- Nutty flavor may be more pleasant than some alternatives
- Especially good for topical uses
- Rich in antioxidants
- High in vitamins A, B, D, and E
- Much thicker than most carrier oils, which may be unpleasant
- Significantly more expensive than many carrier oils
- Higher allergy risk than many carrier oils
Additional Health Claims
Most of the research into avocado oil has been performed on animals, not people. Until researchers take this next step, preliminary evidence suggests that avocado oil may:
- Lower bad cholesterol and raise good cholesterol, which decreases the risk of heart disease
- Improve glucose tolerance and reduce insulin resistance, providing protection from diabetes
- Improve metabolic markers
Avocado oil is less likely than many oils to clog your pores, so it’s popular for topical use. Plus, its slow drying time may help it last longer than some topical preparations.
Avocado allergies are possible. If you experience itching in your mouth after ingesting avocados or avocado oil, don’t ingest any more before talking with your healthcare provider about it. Some allergies tend to occur together. People with avocado allergies may be especially sensitive to:
- Other fruits and vegetables
If you have an allergic reaction to any of these things, you should be tested for a reaction to the others as well.
Extreme Symptoms Are Possible
Extreme allergy symptoms, such as difficulty breathing or anaphylaxis, are uncommon (but possible) with avocados because digestive enzymes tend to break down the allergen before it’s absorbed into your body. Get emergency medical attention if you experience these symptoms.
Carrier oils are important to CBD because they help dissolve the cannabinoid’s molecules so they can be absorbed by the body. Many carrier oils are similar, but they may have differences that could be important to you for various health reasons. One key reason for using a carrier oil is that it improves bioavailability, which means it helps your body absorb CBD oil. Besides, to deliver accurate and consistent doses, it’s easier to measure out a dropperful of CBD-infused oil than a tiny amount of crystalline isolate (which is CBD in pure form). Carrier oils also may have health benefits all on their own. Four common carrier oils are medium-chain triglyceride (MCT) oil, hemp seed oil, olive oil, and avocado oil.
A Word From Verywell
Many people are quick to ask: “Which CBD carrier oil is the best?” Now you know that the answer depends on several factors, including the type and uses of the CBD product, whether you have allergies or certain health conditions, and your personal preferences. So look at it this way: If you try one oil and don’t like it, you can always try a different one. Meanwhile, be sure to ask your healthcare provider or pharmacist for advice along the way.
The Benefits Of CBD Oil For Dogs
The good news is that it can help with many of your dog’s health issues from allergies to cancer. The bad news is that the CBD industry for pets is still unregulated. That means the majority of pet owners might be getting ripped off.
So today I want to talk about all the good things CBD oil can do for your dogs. Then I’ll show you how to find the best product for your dog and talk about how to give it.
What Does CBD Oil Do For Dogs?
There’s a messenger system in your dog’s body called the endocannabinoid system. It helps regulate sleep, appetite, pain, the immune system and more. CBD impacts the activity of the messengers in this system and stimulates the nervous, digestive and immune systems, as well as the brain. And it can do this because the endocannabinoids in CBD are very similar to the ones found in your dog’s body.
That’s why the benefits of CBD can be deep and significant. And why CBD oil is the fastest-growing healthy plant in the world!
6 Ways CBD Oil Can Help Your Dog
Let’s take a look at common conditions where CBD can help dogs. And after I’ll talk about which CBD oil you should buy and general dosing information.
1. Dogs With Joint Problems
If your dog has joint pain, your vet might prescribe NSAIDs or other pain meds like Gabapentin. But NSAIDs can cause deterioration in joints and soft tissues … and they can damage your dog’s liver. Gabapentin can also cause kidney damage. Plus, it’s not all that effective.
CBD is a natural anti-inflammatory that doesn’t carry the same risk of side effects as drugs. It works by binding to CB1 receptors in the brain. These receptors stimulate the immune system to reduce inflammation. CB1 receptors also change the way the brain responds to pain.
CBD also binds to CB2 receptors found in the nervous and immune systems. When this happens, the body may produce more cannabinoids naturally. This helps reduce inflammation even more and reduce the pain associated with it.
In fact, researchers at Cornell University found that dogs taking CBD for arthritis were more active and showed a decrease in pain.
Some of the common people buy CBD Oil for dogs as an anti-inflammatory for joint problems include:
- Hip and elbow dysplasia
- Sprains and strains
- Torn ligaments (CCL)
2. Dogs With Cancer
Sadly, 50% of adult dogs will get cancer. Cancer is a massive health challenge for dogs, especially if they undergo chemotherapy or radiation.
Cancer researchers are always looking for new ways to treat cancer and release the pain and nausea that can go with it. And CBD has been extensively researched as a cancer-fighting substance.
A study in mice showed that CBD slowed the growth of mammary cancer cells. And in 2018, researchers found that CBD increased survival time in mice with pancreatic cancer. Other animal studies show CBD oil has cancer-fighting abilities and can slow the growth of tumors.
In another study, cancer cells became more sensitive to treatment with CBD. That means CBD can increase the effectiveness of conventional cancer treatments.
CBD also kills cancer cells by blocking their ability to produce energy. And it can stimulate the immune system to produce killer cells that cause death in cancer cells.
Researchers also found that CBD blocks a cannabinoid receptor called GPR55. This is important because GPR55 increased the growth rate of cancer cells in mice.
CBD oil can also help with nausea associated with many cancer treatments. And studies have shown CBD can significantly reduce cancer-related pain.
3. Dogs With Seizures And Epilepsy
It’s estimated that about 5% of dogs suffer from seizures. They can be terrifying for both dogs and their humans … and they can cause anxiety.
Most vets treat epilepsy and seizures with antiepileptic drugs. Common options are phenobarbital or potassium bromide. But these drugs are extremely harmful to your dog’s liver and other organs. And even if the drugs don’t cause unmanageable side effects, they don’t always work …
So researchers at Colorado State University got excited when they studied CBD as a treatment for epilspsy in dogs. A whopping 89% of dogs that received the CBD had a reduction in seizures.
In human trials, CBD even worked in patients with drug-resistant epilepsy. In one study, 7 out of 8 patients saw a marked improvement within 4 to 5 months.
CBD reduces the frequency and severity of seizures because of how it interacts with the endocannabinoid system. It’s believed that abnormal electric charges of the neurons in the nervous system cause seizures. But CBD can bind to receptors in the brain … researchers speculate this can improve the functioning of the nervous system.
4. Dogs With Anxiety
Anxiety is a common reason dog owners turn to CBD. Anxiety can appear in different forms, including:
- Noise phobia
- Separation anxiety
Of course, there are anti-anxiety drugs available … but CBD is being studied for anxiety because it doesn’t carry dangerous side effects.
Most human users of CBD take it for pain, anxiety and depression. Over a third of these users report that CBD worked “very well by itself.” CBD has even helped manage anxiety and insomnia in children with post-traumatic stress disorder (PTSD). And animal studies show its antidepressant effects aren’t just for people.
CBD can work quickly given directly by mouth when your dog gets stressed. It usually only takes 5 to 20 minutes to work. But CBD appears to be most beneficial for anxiety when given over a period of time. So if your dog is prone to stress, a daily dose might work best.
A 2012 study looked at stress in rats exposed to cats. The rats given repeated doses of CBD had less anxiety than those given a single dose.
Researchers aren’t certain how CBD relieves stress and anxiety, but it’s thought that it can help regulate serotonin. Serotonin is a hormone that regulates mood, social behavior, digestion, sleep and appetite.=
5. Dogs In Pain
Probably the most promising research on CBD is that done on pain. From nerve pain to arthritis, it works well … without the harmful side effects of pain medications.
CBD binds to both CB1 and CB2 receptors in the brain and nervous system and this helps change the way your dog’s brain perceives pain. Plus, CBD can help manage the other symptoms that accompany pain, such as sleeplessness and nausea.
CBD can also help manage acute pain from injuries.
6. Dogs With Allergies
Allergies are on the rise in dogs. And they’re difficult to treat … so, sadly, allergies are a common reason dogs are euthanized. Skin conditions in general are one of the most frequent reasons for vet visits.
The endocannabinoid system is also found in the skin … and that’s good news for dogs with allergies. It means CBD can help relieve dry and itchy skin. And it can promote the growth of new healthy skin cells.
You can give CBD internally for allergies, or use it externally for hot spots or interdigital cysts.
Now that you know a bit more about WHY you would give your dog CBD oil to your dog, let’s about HOW to choose a good quality product.
How To Choose The Best CBD Oil For Your Dog
CBD (Cannabidiol) is a naturally found substance in cannabis and hemp. Both deliver amazing health benefits … but there are differences.
Cannabis (marijuana) contains a relatively large amount of THC (tetrahydrocannabinol). THC is what causes the psychoactive activities of cannabis. It’s why marijuana can give a “high” or “buzz.”
CBD oil made from hemp contains much lower amounts of THC. To sell hemp legally, it must contain less than 0.3% THC. So while your dog can still enjoy the calmness and reduction in anxiety that CBD provides, he won’t get high. And that’s important … because you might enjoy the high, but your dog definitely doesn’t!
Your dog will also get the same pain-relieving and immune-supporting benefits from hemp CBD.
But not all hemp CBD products are the same …
1. Look For A Full Or Broad Spectrum Hemp
Check the label of your CBD product to make sure it’s full spectrum or broad spectrum.
This means your dog’s CBD oil contains not just CBD, but other important cannabinoids that occur naturally in full-spectrum hemp. This includes CBC (Cannabichromene) and CBG (Cannabigerol).
Researchers have looked at CBC for its …
- Cancer-fighting activities
- Ability to block pain and inflammation
- Positive effect on brain cells
CBG is also studied for its medicinal use. It can decrease inflammation in the digestive tract and it can protect nerve cells and the eyes. It also supports healthy bladder function and fights cancer cells.
A full-spectrum CBD oil will also contain terpenes such as limonene, alpha-pinene, and beta-pinene. These are also naturally occurring medicinal substances found in all hemp.
Together, cannabinoids and terpenes create the entourage effect. This happens when compounds in hemp oil work synergistically to boost the medicinal properties of hemp oil.
CBD extracted with CO2 (I’ll talk about this in a moment) pulverizes the terpenes. This will make them hard to detect in testing and they won’t show up on the Certificate Of Analysis …
… but they’ll still be there and will contribute to the CBD oil’s medicinal effects.
CBD extracted with solvents will better preserve the terpenes. So you will find them noted on the Certificate Of Analysis.
But I don’t recommend solvent extracted products, which leads me to my next point …
2. Make Sure Your Dog’s CBD Uses CO2 Extraction
There are two common ways to extract the CBD oil from the hemp plant:
As you’ve probably guessed, CO2 extraction uses carbon dioxide to extract oil from the plant. Using a high-pressure chamber, CO2 puts pressure on the hemp. This breaks down the hemp and releases the oil.
This method of extraction creates oils with a higher concentration of CBD. That means your dog will get more from his supplement. Of course, that also makes the product more expensive … but it’s better than the alternative.
The cheapest way to extract oil from the hemp plant is with solvents, such as …
- Petroleum products
But residue from these solvents will be in the product and they can be toxic to your dog.
Some CBD extraction uses natural solvents, such as ethanol or olive oil. This is much safer for your dog but these oils can destroy the hemp plant’s waxes and the resulting oil isn’t as beneficial.
3. Look For A Certificate Of Analysis
If your dog’s CBD oil doesn’t have a certificate of analysis (COA), run away!
A certificate of analysis is a document that shows the amount and type of cannabinoids in the CBD product. And it usually comes from a third-party laboratory,
COAs protect your dog from poor quality products and the manufacturer should have one for each batch of hemp. If there isn’t a COA on the company’s website, you’ll want to ask for one before you buy any CBD oil.
When looking at the COA, there are 5 important things to look for.
CBD Is The Same As Advertised
This is more common than you would think … in fact, we were once tricked by this!
What you might see is something like “500 mg CBD” on the product label. But don’t take the label at face value! Make sure the COA says the same amount as the label does.
Some lab tests express the CBD content in mg/g. So to calculate the amount of CBD, you need to know how many grams are in the bottle of CBD.
For example, let’s say the COA shows 16.9 mg/g CBD. To calculate how much CBD is in the product, multiply the number of mg/g by the number of grams the bottle weighs. (A typical 1-ounce dropper bottle of CBD will weigh 30 grams.) This will give you the total mg of CBD in the bottle. In this example, it’s 507 mg (16.9 mg/g x 30 gram bottle).
CBD Is Really Full Spectrum
Again, never take the label at face value! Some CBD is from isolate, which means it won’t have other important cannabinoids and terpenes.
Remember the entourage effect? You won’t get this extra boost with CBD isolate. So how do you find out if your dog’s CBD is from isolate? The COA will show that the product only contains CBD and no other cannabinoids. Stay away from these products.
There’s Not Too Much (Or Too Little) THC
If your dog’s CBD contains more than 0.03% THC, it’s probably marijuana and not hemp. It’s not legal and your dog won’t enjoy the psychoactive effects.
You also want to avoid products with zero THC. If there’s none, then your dog’s CBD is from isolate … and the health benefits will be fewer.
A Third-Party Did The Tests
Once again, never take the manufacturer’s word that the product is high quality. Make sure the product was properly tested by a third party lab. Unfortunately, the CBD industry isn’t regulated, which leaves you vulnerable to poor products.
There’s No Contaminants
You need to know where and how the hemp that’s used to make the CBD oil is grown. This plays a huge role in those test results you see in the COA.
Always look for an organic product to reduce any environmental toxin risks. You want to know that the soil and water it’s grown in is as clean as possible. That’s because hemp plants are really good sponges and can absorb contaminants as they grow. And it’s why heavy metal toxicity can be a concern when looking at CBD oils.
So be sure that you check the COA for any contaminants such as pesticides, heavy metals and solvent residues.
Cost Shouldn’t Be A Priority
It can be hard to compare products and some people give up and look at costs only …
… but this is not the best approach!
You want a high-quality and safe product for your dog. Extracting CBD from hemp requires a lot of plant material as well as careful monitoring.
If the product you’re considering has a price that’s significantly lower than the competition, there’s probably a reason for that …
But the most expensive doesn’t mean it’s the best CBD oil for dogs …
Instead, consider what we’ve reviewed …
- How was the CBD oil extracted? (CO2 is best.)
- Is the CBD concentration different than advertised? (CBD on COA should match the bottle.)
- Is it full-spectrum? (The product should have other cannabinoids, not just CBD.)
- Is the THC content worrisome? (THC should be less than 0.3% but higher than 0%.)
- Is it organic? (Hemp is a sponge for contaminants.)
- Was it third party tested? (If you can’t find a COA online, ask the manufacturer for one.)
These variables are what you need to look for when determining the quality of a product. The cost is never a sure sign of a product’s quality.
Side Effects Of CBD Oil For Dogs
The American Holistic Veterinary Medical Association surveyed dog owners. They wanted to see what, if any, side effects they noticed. And the great news is that there weren’t any major effects reported.
The most consistent side effects noticed were:
- Sedation 19%
- Overactive appetite 5%
- Lack of energy 4%
- Panic reactions 2.7%
- Dry mouth/excessive drinking 2.3%
- Nausea 1.7%
- Vomiting 1.7%
- Increased seizures 0.69%
- Impaired mental functioning 0.68%
This means the most likely side effect you may see is that your dog gets sleepy. And that isn’t a bad thing. Especially if your dog suffers from seizures, anxiety, or has any pain, and you’d like to give CBD oil a try …
… but some CBD oils will have other additives and may not be safe.
Caution With CBD Oil Additives
You want to be sure there are no chemical additives or preservatives in the product you buy. These will cancel out the health benefits, even if the hemp is grown organically.
Also be aware of companies who have added essential oils (EOs) to their CBD oil. Even though they’re “natural,” EOs can affect animals profoundly.
If your holistic vet has recommended using a CBD oil with an EO, then follow her dosing recommendations. She’ll know what’s best for your dog’s unique health needs.
Some will recommend using CBD with frankincense as it’s good for tumor reduction in cancer patients. But always check with your holistic vet or herbalist first.
Dogs Taking Other Medications Or Supplements
If your dog is taking any other medications or supplements you will want to check with your holistic vet as well. CBD oil has many health benefits but it can change how your dog metabolizes some medications or supplements.
Researchers have looked at how CBD oil changes metabolism in humans. It can be similar to grapefruit, which causes significant reactions. So if your dog is taking any of the following medications you’ll need to ask your vet about dose changes:
- Allergy medications
- Liver or kidney medications
- Heart medications
- Anxiety medications
Hopefully, your holistic vet has helped you find alternatives to the medications above. But even then … CBD can affect herbs and natural supplements.
This doesn’t mean you can’t give your CBD oil if he uses other supplements or medications. You may just need to make adjustments. CBD changes the metabolism of other things but sometimes for the better! Meaning you can use less of another product or skip on the medications altogether.
And less is often more.
CBD Oil Dosage For Dogs
Each bottle of CBD has a specific concentration expressed in milligrams (mg). Most dogs are okay with the taste, so you can just put it on your dog’s food.
Dr Robert Silver recommends giving your dog 0.05 to 0.25 mg/pound of body weight, twice daily. He also suggests starting with a lower dose and working your way up. If 0.05 mg/pound is enough, stay at that dose. There’s no need to increase unless the lower dose stops working. If that happens, increase the dose to 0.125 mg/pound, twice daily and only continue to increase if your dog needs it.
For anxiety or health prevention, you’ll usually find that the lower doses work well. But if your dog is dealing with pain or immune issues, you’ll probably need a larger amount.
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CBD oil for dogs is a natural, safe remedy that can help your dogs with pain, anxiety, caner, seizures and more.
McAllister SD, Christian RT, Horowitz MP, Garcia A, Desprez PY. Cannabidiol as a novel inhibitor of Id-1 gene expression in aggressive breast cancer cells. Mol Cancer Ther. 2007 Nov;6(11):2921-7.
Corroon J, Phillips JA. A cross-sectional study of cannabidiol users. Cannabis and Cannabinoid Research. 2018;3(1).
Aviello G, Romano B, Borrelli F, Capasso R, Gallo L, Piscitelli F, Di Marzo V, Izzo AA. Chemopreventive effect of the non-psychotropic phytocannabinoid cannabidiol on experimental colon cancer. J Mol Med (Berl). 2012 Aug;90(8):925-34.