Cannabis, cannabinoids and cancer – the evidence so far
Few cancer topics spark as much online debate as cannabis.
The bottom line is that right now there isn’t enough reliable evidence to prove that any form of cannabis can effectively treat cancer in patients. This includes hemp oil, cannabis oil or the active chemicals found within the cannabis plant (cannabinoids) – whether natural or man-made.
Many researchers worldwide are actively investigating cannabinoids, and Cancer Research UK is supporting some of this work. These studies use highly purified chemicals found in the cannabis plant, or lab-made versions of them, and there is genuine interest in these as potential cancer treatments. But this is very different to street-bought cannabis and hemp oil available online or on the high street, for which there is no evidence of any impact on cancer.
Cannabis is still classified as a class B drug in the UK, meaning that it is illegal to possess or supply it. Cancer Research UK can’t comment on the legal status of cannabis, its use as a recreational drug, or its medical use in any other diseases. But we are supportive of properly conducted scientific research into cannabis and its derivatives that could benefit cancer patients.
Unfortunately, there are many unreliable sources of information about cannabis, particularly online. This post contains up-to-date, evidence-based information on cannabis and cancer, so with lots to cover, this is a long article. To help you find what you’re interested in, follow the links below to different sections. Or read on for everything you need to know about cannabis and cancer.
Cannabis and cannabinoids – what are they?
Cannabis is a plant known by many names, including marijuana, pot, grass, weed, hemp, hash or dope.
The plant produces a resin that contains complex chemicals called cannabinoids.
The two main cannabinoids are:
- Delta-9-tetrahydrocannabinol (THC) – a psychoactive substance that can affect how the brain works, creating a ‘high’ feeling.
- Cannabidiol (CBD) – may relieve pain, lower inflammation and decrease anxiety without any psychoactive effects.
Cannabinoids lock on to molecules on the surface of cells called cannabinoid receptors. As well as cannaibinoids found in plant resin, our body produces cannabinoid chemicals – called endocannibinoids – which also attached to these receptors. These receptors are involved in many processes throughout the body, from appetite to the sensation of pain.
Through many detailed experiments – summarised in this Nature Reviews Cancer article – scientists have discovered that both natural and synthetic cannabinoids have a wide range of effects on cells, which is why there’s interest in if cannabis can treat diseases like cancer, as well as help relieve side effects.
Can cannabinoids treat cancer?
Many hundreds of scientific papers looking at cannabinoids and cancer have been published so far, but these studies simply haven’t found enough robust scientific evidence to prove that these can safely and effectively treat cancer.
Research is still ongoing though, with hundreds of scientists investigating the potential of cannabinoids in cancer and other diseases as part of The International Cannabinoid Research Society. And in 2015 the scientific journal Nature published a supplement of review articles about various aspects of cannabis. It’s free to access.
Much of the research into cannabinoids and cancer so far has been done in the lab
Claims that there is solid “proof” that cannabis or cannabinoids can cure cancer is highly misleading.
This is because virtually all the scientific research investigating whether cannabinoids can treat cancer has been done using cancer cells grown in the lab or animals. While these studies are a vital part of research, providing early indications of the benefits of particular treatments, they don’t necessarily hold true for people.
So far, the best results from lab studies have come from using a combination of highly purified THC and cannabidiol (CBD), a cannabinoid found in cannabis plants that counteracts the psychoactive effects of THC. But researchers have also found positive results using man-made cannabinoids, such as a molecule called JWH-133.
There have been intriguing results from lab experiments looking at a number of different cancers, including glioblastoma brain tumours, prostate, breast, lung, and pancreatic cancers. But the take-home message is that different cannabinoids seem to have different effects on various cancer types, so they are far from being a ‘universal’ treatment.
There’s also evidence that cannabinoids have unwanted effects. Although high doses of THC can kill cancer cells, they also harm crucial blood vessel cells. And under some circumstances, cannabinoids can encourage cancer cells to grow, or have different effects depending on the dose used and levels of cannabinoid receptors present on the cancer cells.
Cannabis in clinical trials
To robustly test the potential benefits of cannabinoids in cancer, clinical trials in large numbers of people with control groups of patients – who aren’t given the treatment in question – would be needed.
A few small clinical trials have been set up to test the benefits of cannabinoids for people with glioblastoma multiforme. Results published from a pilot clinical trial where 9 people with advanced, incurable glioblastoma multiforme – the most aggressive brain tumour – were given highly purified THC through a tube directly into their brain showed that THC given in this way is safe and doesn’t seem to cause significant side effects. But as this was an early stage trial without a control group, it couldn’t show whether THC helped to extend patients’ lives.
And a second clinical trial, supported through our Experimental Cancer Medicine Centre (ECMC) Network, tested whether Sativex (nabiximols), a highly purified pharmaceutical-grade extract of cannabis containing THC, CBD, and other cannabinoids could treat people with glioblastoma multiforme brain tumours that have come back after treatment.
In 2021, scientists reported the final results of this phase 1 study to treat people with recurrent glioblastoma with Sativex in combination with the chemotherapy drug, temozolomide. Researchers found that adding Sativex (patients were allowed to choose the amount they took) had acceptable levels of side effects, which included vomiting, dizziness, fatigue, nausea and headache. They also observed that more patients were alive after one year using Sativex (83%) compared to those taking the placebo (44%). However, this phase 1 study only involved 27 patients, which was too small to confirm any potential benefits of Sativex, and was intended to find out if it was safe to take by patients.
This trial is being extended into phase 2 (known as ARISTOCRAT) to explore if this treatment is effective and which patients are most likely to respond to this treatment. If the trial is , it is set to launch at 15 NHS hospitals in 2022, with over 230 patients to be recruited. To find out more about this work, you can listen to our podcast – That Cancer Conversation – where we hear from Professor Susan Short, one of the researchers leading this study.
We’ve also supported a trial that’s testing the benefits of a man-made cannabinoid called dexanabinol in patients with different types of advanced cancer. The trial finished recruiting in 2015 and researchers established a safe dose of the drug, but further development of the drug was stopped due to a lack of evidence around the drug’s effectiveness. Full trials results are yet to be published.
There are still many unanswered questions around the potential for using cannabinoids to treat cancer. It’s not clear:
- which type of cannabinoid – either natural or synthetic – might be most effective
- what kind of doses might be needed
- which types of cancer might respond best to cannabinoids
- how to avoid the psychoactive effects of THC
- how best to get cannabinoids, which don’t dissolve easily in water, into cancer cells
- whether cannabinoids will help to boost or counteract the effects of chemotherapy
These questions must be answered for cannabinoids to be used as safe and effective treatments for cancer patients. It’s the same situation for the many hundreds of other potential cancer drugs being developed and tested in university, charity and industry labs all over the world.
Without doing rigorous scientific research, we will never sift the ‘hits’ from the ‘misses’. If cannabinoids are to get into the clinic, these hurdles first need to be overcome and their benefits proven over existing cancer treatments.
Can cannabis prevent cancer?
There is no reliable evidence that cannabis can prevent cancer.
There has been some research suggesting that endocannabinoids (mentioned earlier) can suppress tumour growth, and in experiments where mice were given very high doses of purified THC, they seemed to have a lower risk of developing cancer. But this is not enough solid scientific evidence to suggest that cannabinoids or cannabis can cut people’s cancer risk.
Does smoking weed cause cancer?
The evidence is a lot less clear when it comes to whether cannabis can cause cancer.
This is because most people who use cannabis smoke it mixed with tobacco, a substance that we know causes cancer. In the UK, more than three quarters of people who smoke weed reported normally mixing it with tobacco.
This makes it hard to disentangle the potential impact of cannabis on cancer risk from the impact of the tobacco. As of 2021, we can’t be sure whether the increased risk is due to tobacco or whether cannabis also has an independent effect.
We do know from decades of evidence that there is no safe way to use tobacco – it’s addictive and harmful for your health. People who smoke weed mixed with tobacco increase their risk of cancer and other conditions. Tobacco also contains the very addictive substance nicotine. This means people who regularly smoke weed mixed with tobacco may find it harder to stop.
> Read about the free support and quitting tools available to help you to stop smoking for good on our website.
Can cannabis relieve cancer symptoms like pain or sickness?
There’s good evidence that cannabinoids may be beneficial in managing cancer pain and side effects from treatment.
As far back as the 1980s, cannabinoid-based drugs including dronabinol (synthetic THC) and nabilone were used to help reduce nausea and vomiting caused by chemotherapy. But there are now safer and more effective alternatives and cannabinoids tend to only be used where other approaches fail.
In some parts of the world, medical marijuana has been legalised for relieving pain and symptoms (palliative use), including cancer pain. But one of the problems with using herbal cannabis is managing the dose. Smoking cannabis or taking it in the form of tea often provides an inconsistent dose, which may make it difficult for patients to monitor their intake. So, researchers are turning to alternative dosing methods, such as mouth sprays, which deliver a reliable and regulated dose.
Large-scale clinical trials in the UK have been testing whether a mouth spray formulation of Sativex (nabiximols) can help to control severe cancer pain that doesn’t respond to other drugs. Results from these didn’t find any difference in self-reported pain scores between the treatment and the placebo.
Cannabinoids may also have potential in combating the loss of appetite and wasting (cachexia) experienced by some people with cancer, although so far clinical evidence is lacking. One clinical trial comparing appetite in groups of cancer patients given cannabis extract, THC and a placebo didn’t find a difference between the treatments, while another didn’t show any benefit and was closed early.
Is Cancer Research UK investigating cannabinoids?
Cancer Research UK has funded research into cannabinoids, notably the work of Professor Chris Paraskeva in Bristol investigating the properties of cannabinoids as part of his research into the prevention and treatment of bowel cancer. He has published a number of papers detailing lab experiments looking at endocannabinoids as well as THC, and written a review looking at the potential of cannabinoids for treating bowel cancer.
We also support Dr Laureano de la Vega, a Cancer Research UK Fellow at the University of Dundee, who in 2019 started to explore if CBD can limit cancer’s ability to spread, using lung and triple negative breast cancer cells grown in the lab.
We’re also involved in the only 2 UK clinical trials of cannabinoids for treating cancer, mentioned above, through our national network of Experimental Cancer Medicine Centres.
Our funding committees have previously received other applications from researchers who want to investigate cannabinoids but these failed to reach our high standards for funding. If we receive future proposals that meet these stringent requirements, then there is no reason that they wouldn’t be funded, assuming we have the money available.
Unfortunately, some scammers are using the email address [email protected] and claiming to be based at our head office, tricking cancer patients and their families into handing over money for “cannabis oil”, after which they receive nothing in return. This is a scam and has nothing to do with Cancer Research UK or our employees, as we wrote about in 2015. If you believe you have been a victim of this fraud, please contact the police.
“It’s natural so it must be better, right?”
There’s no doubt that the natural world is a treasure trove of biologically useful compounds, and there are countless examples where these have been harnessed as effective treatments.
Numerous potent cancer drugs have also been developed in this way – purifying a natural compound, improving it and testing it to create a beneficial drug – including taxol, vincristine, vinblastine, camptothecin, colchicine, and etoposide. But although these purified drugs in controlled high doses can treat cancer, it doesn’t mean that the original plant (or a simple extract) will have the same effect. So, although cannabis contains certain cannabinoids, it doesn’t automatically follow that cannabis itself can treat cancer.
“But it worked for this patient…”
Doctors sometimes publish case reports about extraordinary or important observations they have seen in their clinic. For example, there is a published case report of a 14-year old girl from Canada who was treated with cannabis extracts (also referred to as “hemp oil”). But very little reliable information can be taken from a single patient treated with what’s an unknown mix of cannabinoids outside of a controlled clinical setting.
There are also many videos and anecdotes online claiming that people have been completely cured of cancer with cannabis, hemp/cannabis oil or other cannabis derivatives.
Despite what these sources may claim, it’s impossible to tell whether these patients have been ‘cured’ by cannabis or not. There is usually no information about their medical diagnosis, stage of disease, what other cancer treatments they had, or the chemical make-up of their treatment. These sources also only publish the “success stories”, and don’t share how many people who used cannabis or its derivatives had no benefit, or worse, were potentially harmed.
Robust scientific studies describe the detail of experiments and share the results – positive or negative. This is vital for working out whether a potential cancer treatment is truly safe and effective, or not. And publishing this data allows doctors around the world to judge the information for themselves and use it for the benefit and safety of their patients.
This is the standard to which all cancer treatments are held, and it’s one that cannabinoids should be held to, too.
Dr Wai Liu at St George’s University is researching cannabis and cannabinoids for treating cancer to build up the evidence. He is happy to collect individual stories from UK patients and can be contacted by email. In the US, the Office of Cancer Complementary and Alternative Medicine gathers similar stories for their Best Case Series.
“What’s the harm? There’s nothing to lose.”
If someone chooses to reject conventional cancer treatment in favour of unproven alternatives, including cannabis, they may miss out on treatment that could save or significantly lengthen their life. They may also miss out on effective symptom relief to control pain or other problems.
Many of these unproven therapies are also expensive, and aren’t covered by the NHS or medical insurance. In the worst cases, an alternative therapy may even hasten death.
Although centuries of human experimentation tell us that naturally-occurring cannabinoids are broadly safe, they are not without risks. They can increase heart rate, which may cause problems for patients with pre-existing or undiagnosed heart conditions. They can also interact with other drugs in the body, including antidepressants and antihistamines. And they may also affect how the body processes certain chemotherapy drugs, which could cause serious side effects.
Cannabis is an illegal (class B) drug in the UK and there are further risks associated with using black market or home-made preparations, particularly cannabis oil, such as toxic chemicals left from the solvents used in the preparation process.
There are also many internet scams by people offering to sell cannabis preparations. As well as the risk of getting something with completely unknown chemical or medicinal properties and unknown effectiveness, scammers are tricking cancer patients and their families into handing over money for “cannabis oil” which they then never receive.
We understand the desire to try every possible avenue when conventional cancer treatment fails. But there is little chance that an unproven alternative treatment bought online will help, and it may well harm. We recommend that cancer patients talk to their doctor about clinical trials that they may be able to join, giving them access to new drugs in a safe and monitored environment.
“Are cancer charities hiding cannabis as a cure?”
We’ve blogged previously about how unjust this is to the thousands of scientists, doctors and nurses working as hard as they can to beat cancer, and to the many thousands of people in the UK and beyond who give up their time and money to fund our work.
History shows that the best way to beat cancer is through rigorous scientific research. This approach has helped to change the face of cancer prevention, diagnosis, treatment, leading to survival doubling over the past 40 years.
As a research-based organisation, we want to see reliable scientific evidence to support claims made about any cancer treatment, be it conventional or alternative. This is vital because lives are at stake. Some people may think that a cancer patient has nothing to lose by trying an alternative treatment, but there are big risks.
“Big Pharma can’t patent it so they’re not interested.”
Some people argue that the potential of cannabinoids is being ignored by pharmaceutical companies, because they can’t patent the chemicals naturally occurring in cannabis plants. But there are many ways that these compounds can be patented – for example, by developing more effective lab-made versions or better ways to deliver them.
Other people argue that patients should be treated with ‘street’ or homegrown cannabis preparations, and that the research being done by companies is solely to make money and prevent patients accessing “the cure”.
But the best chance of ensuring that the potential benefits of cannabinoids – whether natural or man-made – can be brought to patients is through research using quality-controlled, safe, legal, pharmaceutical grade preparations containing known amounts of the drugs.
This requires time, effort and money, which may come from companies or independent organisations such as charities or governments. And, ultimately, this investment needs to be paid back by sales of a safe, effective new drug.
It’s true that there are issues around drug pricing and availability and we’re pushing for companies to make new treatments available at a fair price. We would hope that if cannabinoids were to be shown to be safe and effective enough to make it to the clinic, they would be made available at a fair price for all patients who might benefit from them.
“Why don’t you campaign for cannabis to be legalised?”
Cannabis is classified as a class B drug in the UK, meaning that it is illegal to possess or supply it.
Cancer Research UK does not have an organisational policy on the legal status of cannabis, its use or abuse as a recreational drug, or its medical use in any other diseases. But we are supportive of properly conducted scientific research into cannabis and its derivatives that could benefit cancer patients and we will continue to monitor developments in the fields and evidence as it emerges.
Right now, there simply isn’t enough evidence to prove that cannabinoids – whether natural or synthetic – can effectively treat cancer in patients, although research is ongoing. And there’s certainly no evidence that ‘street’ cannabis can treat cancer.
We’re supportive of properly conducted scientific research into cannabis and its derivatives that could benefit cancer patients. Many researchers are actively exploring this approach, and Cancer Research UK is supporting, and will continue to support, scientifically robust research into cannabis and cannabinoids that reaches the high-quality standards set by our funding committees.
References and further reading:
- CancerHelp UK – Does smoking cannabis cause cancer?
- CancerHelp UK – Is cannabis a treatment for brain tumours?
- CancerHelp UK – Twotrials of Sativex for cancer-related pain
- National Cancer Institute (US) – Information about cannabis and cannabinoids for cancer patients
- National Cancer Institute (US) – Information about cannabis and cannabinoids for health professionals
- Velasco, G., Sánchez, C. & Guzmán, M. (2012). Towards the use of cannabinoids as antitumour agents, Nature Reviews Cancer, 12 (6) 444. DOI: 10.1038/nrc3247
- Sarfaraz, S. et al (2008). Cannabinoids for Cancer Treatment: Progress and Promise, Cancer Research, 68 (2) 342. DOI: 10.1158/0008-5472.CAN-07-2785
- Guindon, J. & Hohmann, A.G. (2011). The endocannabinoid system and cancer: therapeutic implication, British Journal of Pharmacology, 163 (7) 1463. DOI: 10.1111/j.1476-5381.2011.01327.x
- Engels, F.K. et al (2007). Medicinal cannabis in oncology, European Journal of Cancer, 43 (18) 2644. DOI: 10.1016/j.ejca.2007.09.010
- Twelves, C., Sabel, M., Checketts, D. et al (2021). A phase 1b randomised, placebo-controlled trial of nabiximols cannabinoid oromucosal spray with temozolomide in patients with recurrent glioblastoma. British Journal of Cancer 124, 1379–1387. DOI: 10.1038/s41416-021-01259-3
- Cannabinoids in the treatment of chemotherapy-induced nausea and vomiting – Todaro (2012) Journal of the National Comprehensive Cancer Network
- Bowles, D.W. et al (2012). The intersection between cannabis and cancer in the United States, Critical Reviews in Oncology/Hematology, 83 (1) 10. DOI: 10.1016/j.critrevonc.2011.09.008
- Hall, W., Christie, M. & Currow, D. (2005). Cannabinoids and cancer: causation, remediation, and palliation, The Lancet Oncology, 6 (1) 42. DOI: 10.1016/S1470-2045(04)01711-5 . , Wai Liu, The Conversation
Until you’re a terminal cancer patient you just wont understand the desperation to live as long as possible, even if it were mere days extra time. I would try anything for extra time with loved ones.
I can’t believe there isn’t more research into cannabis and cancer. And for those that say “well it doesn’t work for everybody” guess what conventional cancer treatment doesn’t either.
Stage 4 cancer = no cure, terminal in most cases.
Why is it that charities raking in millions every year can find the evidence of cannabis for not treating cancer but cant find the overwhelming evidence that it can and does treat cancer ?
Great reading I have lung cancer I’m being treated with chemo now and would be interested in a trail it’s small cell lung cancer
Without full spectrum cannabis oil my life around a year into breast cancer I doubt I would be here now
It has enabled me to come off opioids and live a semi normal life
It sickens me to think drs happily give out meds that are killing people but won’t give out a herb that has O deaths yes Zero
I have even contacted professor Mike barns pleading with him to help me find a trial but guess what not one in the uk
The fact cannabis is illegal in this county is all political and NOTHING to do with our health
It’s about time charity’s like yours start campaigning for us, most of us medical cannabis users are spending far to much on it in order to feel well I echo what another commenter said that all stage 4 should be at least offered cannabis as an alternative
Also why can’t the hospital doctors give medical cannabis too relieve sickness and pain of cancer it’s cruel
I think that medical cannabis should be given too all stage 4 cancer patients that are told it’s aggressive and treatment wont help under medical care it could be done safely then with trial an error they will know if it works legalise cannabis for the sick wake up Boris
Thank you for sharing this amazing blog. It is easy to learn and understand. It’s a truly useful blog.
“Why don’t you campaign for cannabis to be legalised?” Your answer was ridiculous that’s all you said was that it’s illegal to possess or buy or what ever I think the question was why won’t you campaign to have it legal so then it can be tested more . Don’t beat around the bush ( No pun intended) just say it’s not worth the effort for the money you would have to spend .
this blog post is very perfect and has a lot of very vital info, thanks so much for this work
We’ve recently seen stories in the press claiming that the US government has “admitted that cannabis kills cancer” (for example, this one in the Metro), based on the observation that pages on the US National Cancer Institute information website carry details of the current scientific evidence around the effects of cannabis and cannabinoids on cancer cells in the lab and animal models.
The first thing to point out is that the NCI’s cancer information website is an independent resource for doctors and the patients, and is not a statement of NIH, NCI or US government policy.
Furthermore, the information on these pages isn’t new, nor is it an ‘admission’ of any kind: the scientific evidence about cannabis, cannabinoids and cancer, which these media stories are referring to, has been openly published on the NCI’s website for several years – for example, see this page from the same section of the NIH website on cannabis and cannabinoids from 2011, accessed via the internet archive.
We often see websites with long lists of scientific papers claiming that cannabis is a “cure” for various cancers. However, when we look at the detail of the data and the experimental detail of the research, it becomes clear that although they may be interesting and build evidence to show that cannabinoids may one day bring benefits for cancer patients, they are far from being a cure.
The main point to realise is that virtually all these studies have been done in cancer cells grown in the lab or in animals. These are quite artificial systems and are much less complex than a real cancer growing in a patient.
For example, most experiments with cells grown in the lab use cancer cells that were originally taken from a tumour many years ago, but have been grown for a long time in the lab – known as cell lines. One problem with such cells is that they are all very similar on a genetic and molecular level, but we know that in real cancers, the cells can be very different from each other and respond in different ways to treatments. Also the usual way of testing cannabinoids in animals has been done by transplanting cancer cells (either mouse or human) into mice. Usually only a small number (5-20) will be used for each experiment.
There’s growing evidence that these particular kinds of models (known as xenografts) aren’t as good at suggesting a treatment could work, compared to more sophisticated genetically engineered animals, as they don’t accurately represent the situation in real tumours. So although these kinds of experiments can point towards useful approaches, as well as revealing the underlying molecular ‘nuts and bolts’ of what’s going on, they can’t tell us if something will definitely treat cancer effectively and safely in human patients. They do not “prove that cannabis cures cancer”, as the headlines would have us believe.
Put simply, Petri dishes are not people. Most chemicals that show promise in lab or animal experiments turn out not to work as well as hoped when tested in patients. These kinds of human studies, known as clinical trials, are the only way we can really know if a cancer treatment is effective. There’s more about clinical trials on our website: http://www.cancerresearchuk.org/cancer-help/trials/types-of-trials/
It’s also important to think about what’s being claimed when people use the word “cure”. To most people, including us, this means that a cancer is completely treated and does not come back. When we look at the data in the papers listed below, none of them come close to showing these kinds of results. For the experiments involving cells grown in the lab, a proportion of the cells are killed or stop growing, but some of them carry on. Similarly in animal experiments, there is no data that shows a 100 per cent success rate for cannabinoids. For example, most mice treated with cannabinoids will still have tumours, although the cancers may be growing more slowly and spread less in some of them.
This isn’t just true for cannabinoids – it’s true for virtually all cancer drugs used today. Cancer is a very complex biological problem – there are hundreds of different types of cancer, each with important molecular and genetic differences. There’s good evidence to show that every individual’s cancer is as unique as they are, and that tumours can evolve and change within the body to become resistant to treatments.
We know that cancer drugs don’t work for everyone all the time – that’s why there’s so much effort going on to find more effective treatments – but it’s vital that doctors have a solid body of evidence showing how well the treatments they’re using are likely to work. If you or someone you loved were going to take any kind of drug, would you be happy if it had only been tested in very high doses on cancer cell lines grown in the lab, or in mice injected with cancer cells? Or would you want to know that it had been trialled in large numbers of people, and there was good data on how effective it is, whether it’s safe in the dose given, what the side effects are, and the proportion of people that can be expected to get better?
This kind of evidence can only come from a combination of lab studies leading to clinical trials. At the moment, while there are hundreds of interesting lab studies of cannabinoids (just some of which are included in the list below) there is only one clinical trial that has been published. So for now, cannabinoids, whether natural or synthetic, are a very long way from being what we would describe as a “cure” for any type of cancer.
We’ve looked at each of the papers in one of the commonly-seen lists (for example, here), and noted down the kinds of experiments they are. Many of them are available as open access papers, so it’s possible to look at the data for yourself. Hopefully this is a useful explanation of the kind of scientific research that is currently ongoing into cannabinoids and cancer, and the process of gathering evidence to show whether a potential cancer therapy works.
Marijuana and Cancer
Marijuana is the name given to the dried buds and leaves of varieties of the Cannabis sativa plant, which can grow wild in warm and tropical climates throughout the world and be cultivated commercially. It goes by many names, including pot, grass, cannabis, weed, hemp, hash, marihuana, ganja, and dozens of others.
Marijuana has been used in herbal remedies for centuries. Scientists have identified many biologically active components in marijuana. These are called cannabinoids. The two best studied components are the chemicals delta-9-tetrahydrocannabinol (often referred to as THC), and cannabidiol (CBD). Other cannabinoids are being studied.
At this time, the US Drug Enforcement Administration (DEA) lists marijuana and its cannabinoids as Schedule I controlled substances. This means that they cannot legally be prescribed, possessed, or sold under federal law. Whole or crude marijuana (including marijuana oil or hemp oil) is not approved by the US Food and Drug Administration (FDA) for any medical use. But the use of marijuana to treat some medical conditions is legal under state laws in many states.
Dronabinol, a pharmaceutical form of THC, and a man-made cannabinoid drug called nabilone are approved by the FDA to treat some conditions.
Types of marijuana compounds
Different compounds in marijuana have different actions in the human body. For example, delta-9-tetrahydrocannabinol (THC) seems to cause the “high” reported by marijuana users, and also can help relieve pain and nausea, reduce inflammation, and can act as an antioxidant. Cannabidiol (CBD) can help treat seizures, can reduce anxiety and paranoia, and can counteract the “high” caused by THC.
Different cultivars (strains or types) and even different crops of marijuana plants can have varying amounts of these and other active compounds. This means that marijuana can have different effects based on the strain used.
The effects of marijuana also vary depending on how marijuana compounds enter the body. The most common ways to use marijuana are in food (edible marijuana) and by smoking or vaping it (inhaled marijuana):
- Edible marijuana: When taken by mouth, such as when it’s used in cooking oils, drinks (beer, tea, vodka, soda), baked goods (biscuits, brownies, cookies), and candy, the THC is absorbed poorly and can take hours to be absorbed. Once it’s absorbed, it’s processed by the liver, which produces a second psychoactive compound (a substance that acts on the brain and changes mood or consciousness) that affects the brain differently than THC. It’s important to know that the amount of THC in foods that have had marijuana added to them is often unknown and getting too much THC might cause symptoms of overdose.
- Inhaled marijuana: When marijuana is smoked or vaporized, THC enters the bloodstream and goes to the brain quickly. The second psychoactive compound is produced in small amounts, and so has less effect. The effects of inhaled marijuana fade faster than marijuana taken by mouth.
How can marijuana affect symptoms of cancer?
A number of small studies of smoked marijuana found that it can be helpful in treating nausea and vomiting from cancer chemotherapy.
A few studies have found that inhaled (smoked or vaporized) marijuana can be helpful treatment of neuropathic pain (pain caused by damaged nerves).
Smoked marijuana has also helped improve food intake in HIV patients in studies.
There are no studies in people of the effects of marijuana oil or hemp oil.
Studies have long shown that people who took marijuana extracts in clinical trials tended to need less pain medicine.
More recently, scientists reported that THC and other cannabinoids such as CBD slow growth and/or cause death in certain types of cancer cells growing in lab dishes. Some animal studies also suggest certain cannabinoids may slow growth and reduce spread of some forms of cancer.
There have been some early clinical trials of cannabinoids in treating cancer in humans and more studies are planned. While the studies so far have shown that cannabinoids can be safe in treating cancer, they do not show that they help control or cure the disease.
Relying on marijuana alone as treatment while avoiding or delaying conventional medical care for cancer may have serious health consequences.
Possible harmful effects of marijuana
Marijuana can also pose some harms to users. While the most common effect of marijuana is a feeling of euphoria (“high”), it also can lower the user’s control over movement, cause disorientation, and sometimes cause unpleasant thoughts or feelings of anxiety and paranoia.
Smoked marijuana delivers THC and other cannabinoids to the body, but it also delivers harmful substances to users and those close by, including many of the same substances found in tobacco smoke.
Because marijuana plants come in different strains with different levels of active compounds, it can make each user’s experience very hard to predict. The effects can also differ based on how deeply and for how long the user inhales. Likewise, the effects of ingesting marijuana orally can vary between people. Also, some chronic users can develop an unhealthy dependence on marijuana.
There are 2 chemically pure drugs based on marijuana compounds that have been approved in the US for medical use.
- Dronabinol (Marinol®) is a gelatin capsule containing delta-9-tetrahydrocannabinol (THC) that’s approved by the US Food and Drug Administration (FDA) to treat nausea and vomiting caused by cancer chemotherapy as well as weight loss and poor appetite in patients with AIDS.
- Nabilone (Cesamet®) is a synthetic cannabinoid that acts much like THC. It can be taken by mouth to treat nausea and vomiting caused by cancer chemotherapy when other drugs have not worked.
Nabiximols is a cannabinoid drug still under study in the US. It’s a mouth spray made up of a whole-plant extract with THC and cannabidiol (CBD) in an almost one to one mix. It’s available in Canada and parts of Europe to treat pain linked to cancer, as well as muscle spasms and pain from multiple sclerosis (MS). It’s not approved in the US at this time, but it’s being tested in clinical trials to see if it can help a number of conditions.
How can cannabinoid drugs affect symptoms of cancer?
Based on a number of studies, dronabinol can be helpful for reducing nausea and vomiting linked to chemotherapy.
Dronabinol has also been found to help improve food intake and prevent weight loss in patients with HIV. In studies of cancer patients, though, it wasn’t better than placebo or another drug (megestrol acetate).
Nabiximols has shown promise for helping people with cancer pain that’s unrelieved by strong pain medicines, but it hasn’t been found to be helpful in every study done. Research is still being done on this drug.
Side effects of cannabinoid drugs
Like many other drugs, the prescription cannabinoids, dronabinol and nabilone, can cause side effects and complications.
Some people have trouble with increased heart rate, decreased blood pressure (especially when standing up), dizziness or lightheadedness, and fainting. These drugs can cause drowsiness as well as mood changes or a feeling of being “high” that some people find uncomfortable. They can also worsen depression, mania, or other mental illness. Some patients taking nabilone in studies reported hallucinations. The drugs may increase some effects of sedatives, sleeping pills, or alcohol, such as sleepiness and poor coordination. Patients have also reported problems with dry mouth and trouble with recent memory.
Older patients may have more problems with side effects and are usually started on lower doses.
People who have had emotional illnesses, paranoia, or hallucinations may find their symptoms are worse when taking cannabinoid drugs.
Talk to your doctor about what you should expect when taking one of these drugs. It’s a good idea to have someone with you when you first start taking one of these drugs and after any dose changes.
What does the American Cancer Society say about the use of marijuana in people with cancer?
The American Cancer Society supports the need for more scientific research on cannabinoids for cancer patients, and recognizes the need for better and more effective therapies that can overcome the often debilitating side effects of cancer and its treatment. The Society also believes that the classification of marijuana as a Schedule I controlled substance by the US Drug Enforcement Administration imposes numerous conditions on researchers and deters scientific study of cannabinoids. Federal officials should examine options consistent with federal law for enabling more scientific study on marijuana.
Medical decisions about pain and symptom management should be made between the patient and their doctor, balancing evidence of benefit and harm to the patient, the patient’s preferences and values, and any laws and regulations that may apply.
The American Cancer Society Cancer Action Network (ACS CAN), the Society’s advocacy affiliate, has not taken a position on legalization of marijuana for medical purposes because of the need for more scientific research on marijuana’s potential benefits and harms. However, ACS CAN opposes the smoking or vaping of marijuana and other cannabinoids in public places because the carcinogens in marijuana smoke pose numerous health hazards to the patient and others in the patient’s presence.