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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.

Unanswered questions

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.

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“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.

In summary

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

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Comments

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.

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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.

Cannabis and Cannabinoids (PDQ®)–Patient Version

Questions and Answers About Cannabis and Cannabinoids

Cannabis, also known as marijuana, is a plant first grown in Central Asia that is now grown in many parts of the world. The Cannabis plant makes a resin (thick substance) that contains compounds called cannabinoids. Some cannabinoids are psychoactive (affects your mind or mood). In the United States, Cannabis is a controlled substance and has been classified as a Schedule I agent (a drug with a high potential for abuse and no accepted medical use).

Hemp is a mixture of the Cannabis plant with very low levels of psychoactive compounds. Hemp oil or cannabidiol (CBD) are made from extracts of industrial hemp, while hemp seed oil is an edible fatty oil that contains few or no cannabinoids. Hemp is not a controlled substance.

See the General Information section of the health professional version of the Cannabis and Cannabinoids summary for more information on medicinal Cannabis products.

Clinical trials that study Cannabis for cancer treatment are limited. To start a clinical trial with Cannabis in the United States, researchers must file an Investigational New Drug (IND) application with the FDA, have a Schedule I license from the U.S. Drug Enforcement Administration, and have approval from the National Institute on Drug Abuse.

By federal law, possessing Cannabis (marijuana) is illegal in the United States unless it is used in approved research settings. However, a growing number of states, territories, and the District of Columbia have passed laws to legalize medical and/or recreational marijuana. (See Question 3).

Cannabinoids, also known as phytocannabinoids, are chemicals in Cannabis that cause drug-like effects in the body, including the central nervous system and the immune system. Over 100 cannabinoids have been found in Cannabis. The main psychoactive cannabinoid in Cannabis is delta-9-THC. Another active cannabinoid is cannabidiol (CBD).

Cannabinoids may help treat the side effects of cancer and cancer treatment.

Although federal law prohibits the use of Cannabis, the map below shows the states and territories that have legalized Cannabis for medical use. Some other states have legalized only one ingredient in Cannabis, such as cannabidiol (CBD), and these states are not included in the map. Medical marijuana laws vary from state to state. Enlarge A map showing the U.S. states and territories that have approved the medical use of Cannabis.

Cannabis may be taken by mouth (in baked goods or as an herbal tea) or may be inhaled. When taken by mouth, the main psychoactive part of Cannabis (delta-9-THC) goes through the liver and is changed into a different psychoactive chemical (11-OH-THC).

When Cannabis is smoked and inhaled, cannabinoids quickly enter the bloodstream. The psychoactive chemical (11-OH-THC) is made in smaller amounts than when taken by mouth.

Clinical trials are studying a medicine made from an extract of Cannabis that contains specific amounts of cannabinoids. This medicine is sprayed under the tongue.

In laboratory studies, tumor cells are used to test a substance to find out if it is likely to have any anticancer effects. In animal studies, tests are done to see if a drug, procedure, or treatment is safe and effective in animals. Laboratory and animal studies are done before a substance is tested in people.

Laboratory and animal studies have tested the effects of cannabinoids in laboratory experiments. See the Laboratory/Animal/Preclinical Studies section of the health professional version of Cannabis and Cannabinoids for information on laboratory and animal studies done using cannabinoids.

No ongoing studies of Cannabis as a treatment for cancer in people have been found in the CAM on PubMed database maintained by the National Institutes of Health.

Small studies have been done, but the results have not been reported or suggest a need for larger studies.

  • An oral spray of Cannabis extract given with temozolomide to treat recurrentglioblastoma multiforme.
  • CBD taken by mouth to treat acute graft-versus-host disease in patients who have undergone allogeneic hematopoietic stem cell transplantation.

Cannabis and cannabinoids have been studied as ways to manage side effects of cancer and cancer therapies.

Nausea and vomiting

Cannabis and cannabinoids have been studied in the treatment of nausea and vomiting caused by cancer or cancer treatment:

  • Delta-9-THC taken by mouth: Two cannabinoid drugs, dronabinol and nabilone, approved by the U.S. Food and Drug Administration (FDA), are given to treat nausea and vomiting caused by chemotherapy in patients who have not responded to standardantiemetic therapy. Clinical trials have shown that both dronabinol and nabilone work as well as or better than other drugs to relieve nausea and vomiting.
  • Oral spray with delta-9-THC and CBD: Nabiximols, a Cannabis extract given as a mouth spray, was shown in a small randomized, placebo-controlled, double-blinded clinical trial in Spain to treat nausea and vomiting caused by chemotherapy.
  • Inhaled Cannabis: Small trials have studied inhaled Cannabis for the treatment of nausea and vomiting caused by chemotherapy.

Newer drugs given for nausea caused by chemotherapy have not been compared with Cannabis or cannabinoids in cancer patients.

There is growing interest in treating children for symptoms such as nausea with Cannabis and cannabinoids, but studies are limited. The American Academy of Pediatrics has not endorsed Cannabis and cannabinoid use because of concerns about its effect on brain development.

Appetite

The ability of cannabinoids to increase appetite has been studied:

  • Delta-9-THC taken by mouth: A clinical trial compared delta-9-THC (dronabinol) and a standard drug (megestrol, an appetite stimulant) in patients with advanced cancer and loss of appetite. Results showed that delta-9-THC did not help increase appetite or weight gain in advanced cancer patients compared with megestrol.
  • Inhaled Cannabis: There are no published studies of the effect of inhaled Cannabis on cancer patients with loss of appetite.

Pain relief

Cannabis and cannabinoids have been studied in the treatment of pain:

  • VaporizedCannabis with opioids: In a study of 21 patients with chronic pain, vaporized Cannabis given with morphine relieved pain better than morphine alone, while vaporized Cannabis given with oxycodone did not give greater pain relief. Further studies are needed.
  • Inhaled Cannabis: Randomized controlled trials of inhaled Cannabis in patients with peripheral neuropathy or other nerve pain found thatinhaled Cannabis relieved pain better than inhaled placebo. A retrospective study of patients who received an anticancer drug for gastrointestinal cancers found that those who also inhaled Cannabis had less nerve pain, including those who took Cannabis before they began the anticancer drug.
  • Cannabis plant extract: A study of Cannabis extract that was sprayed under the tongue found it helped patients with advanced cancer whose pain was not relieved by strong opioids alone. In another study, patients who were given lower doses of cannabinoid spray showed better pain control and less sleep loss than patients who received a placebo. Control of cancer-related pain in some patients was better without the need for higher doses of Cannabis extract spray or higher doses of their other pain medicines. Adverse events were related to high doses of cannabinoid spray.
  • Delta-9-THC taken by mouth: Two small clinical trials of oral delta-9-THC showed that it relieved cancer pain. In the first study, patients had good pain relief, less nausea and vomiting, and better appetite. A second study showed that delta-9-THC could relieve pain as well as codeine. An observational study of nabilone also reported less cancer pain along with less nausea, anxiety, and distress when compared with no treatment. Neither dronabinol nor nabilone is approved by the FDA for pain relief.
  • Non-specific Cannabis products: A randomized controlled trial studied patients with advanced cancer who used Cannabis in addition to opioids early in treatment compared to patients who added Cannabis later in treatment. Patients who were given Cannabis later showed an increase in opioid use during the 3-month study. Opioid use was stable in patients who began Cannabis use earlier. There were no changes in symptoms or adverse effects between the two groups. Over 100 different Cannabis products were given during the study.

Anxiety and sleep

Cannabis and cannabinoids have been studied in the treatment of anxiety.

  • Inhaled Cannabis: A small case series found that patients who inhaled Cannabis had improved mood, improved sense of well-being, and less anxiety. In another study, 74 patients newly diagnosed with head and neck cancer who were Cannabis users were matched to 74 nonusers. The Cannabis users had lower anxiety or depression and less pain or discomfort than the nonusers. The Cannabis users were also less tired, had more appetite, and reported greater feelings of well-being.
  • Oral Cannabis oil: A randomized controlled trial studied two different doses of oral Cannabis oil in patients with brain cancer that could not be removed by surgery or had come back. Physical side effects such as sleep were noted to be better in the 1:1 ratio dose group. Both doses were well tolerated without any adverse effects.

Side effects of Cannabis and cannabinoids can include:

  • Fast heartbeat.
  • Low blood pressure.
  • Muscle relaxation.
  • Bloodshot eyes.
  • Slow digestion.
  • Dizziness.
  • Drowsiness.
  • Depression. . .

Both Cannabis and cannabinoids may be addictive. Symptoms of withdrawal from cannabinoids include:

  • Being easily annoyed or angered.
  • Trouble sleeping.
  • Unable to stay still. .
  • Nausea and cramping (rare).
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These symptoms are mild compared with symptoms of withdrawal from opiates and usually go away after a few days.

Studies on cancer risk from Cannabis use

Studies on the risk of various cancers linked to Cannabis smoking have shown the following:

  • Lung cancer: Because Cannabis smoke contains many of the same substances as tobacco smoke, there are concerns about how inhaled Cannabis affects the lungs. A cohort study of men in Africa found that there was an increased risk of lung cancer in tobacco smokers who also inhaled Cannabis. A population study of lung cancer patients found that low Cannabis use was not linked to an increased risk of lung cancer or other aerodigestive tract cancers.
  • Testicular cancer: A 1970 study interviewed over 49,000 Swedish men aged 19 to 21 years about their personal history of using Cannabis at the time they enlisted in the military and then followed them for up to 42 years. The study did not find a link between those who had “ever” used Cannabis and testicular cancer, but did find that “heavy” use of Cannabis (more than 50 times in a lifetime) was linked to more than twice the risk of testicular cancer. The study was limited by the way data was gathered and did not note whether the testicular cancers were seminoma or nonseminoma types or whether Cannabis use also occurred after enlistment.
  • Bladder cancer: A review of bladder cancer rates in Cannabis users and non-users was done in over 84,000 men who took part in the California Men’s Health Study. After more than 16 years of follow-up and adjusting for age, race, ethnic group, and body mass index, rates of bladder cancer were found to be 45% lower in Cannabis users than in men who did not report Cannabis use.

Larger studies that follow patients over time are needed to find if there is a link between Cannabis use and a higher risk of testicular germ cell tumors.

Studies on Cannabis use and impact on cancer treatment

Few studies have been done to find out how Cannabis interacts with conventional treatment. A retrospective observational study in Israel showed that Cannabis reduced the effect of immunotherapy. A prospective observational study of immunotherapy and Cannabis in patients with metastatic cancer reported that the Cannabis users did not benefit from immunotherapy as much as those who did not use Cannabis.

The U.S. Food and Drug Administration (FDA) has not approved Cannabis or cannabinoids for use as a cancer treatment.

Cannabis is not approved by the FDA for the treatment of any cancer-related symptom or side effect of cancer therapy.

Two cannabinoids (dronabinol and nabilone) are approved by the FDA for the treatment of nausea and vomiting caused by chemotherapy in patients who have not responded to antiemetic therapy.

Current Clinical Trials

Use our clinical trial search to find NCI-supported cancer clinical trials that are accepting patients. You can search for trials based on the type of cancer, the age of the patient, and where the trials are being done. General information about clinical trials is also available.

About This PDQ Summary

About PDQ

Physician Data Query (PDQ) is the National Cancer Institute’s (NCI’s) comprehensive cancer information database. The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries come in two versions. The health professional versions have detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions have cancer information that is accurate and up to date and most versions are also available in Spanish.

PDQ is a service of the NCI. The NCI is part of the National Institutes of Health (NIH). NIH is the federal government’s center of biomedical research. The PDQ summaries are based on an independent review of the medical literature. They are not policy statements of the NCI or the NIH.

Purpose of This Summary

This PDQ cancer information summary has current information about the use of Cannabis and cannabinoids in the treatment of people with cancer. It is meant to inform and help patients, families, and caregivers. It does not give formal guidelines or recommendations for making decisions about health care.

Reviewers and Updates

Editorial Boards write the PDQ cancer information summaries and keep them up to date. These Boards are made up of experts in cancer treatment and other specialties related to cancer. The summaries are reviewed regularly and changes are made when there is new information. The date on each summary (“Updated”) is the date of the most recent change.

The information in this patient summary was taken from the health professional version, which is reviewed regularly and updated as needed, by the PDQ Integrative, Alternative, and Complementary Therapies Editorial Board.

Clinical Trial Information

A clinical trial is a study to answer a scientific question, such as whether one treatment is better than another. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients. During treatment clinical trials, information is collected about the effects of a new treatment and how well it works. If a clinical trial shows that a new treatment is better than one currently being used, the new treatment may become “standard.” Patients may want to think about taking part in a clinical trial. Some clinical trials are open only to patients who have not started treatment.

Clinical trials can be found online at NCI’s website. For more information, call the Cancer Information Service (CIS), NCI’s contact center, at 1-800-4-CANCER (1-800-422-6237).

Permission to Use This Summary

PDQ is a registered trademark. The content of PDQ documents can be used freely as text. It cannot be identified as an NCI PDQ cancer information summary unless the whole summary is shown and it is updated regularly. However, a user would be allowed to write a sentence such as “NCI’s PDQ cancer information summary about breast cancer prevention states the risks in the following way: [include excerpt from the summary].”

The best way to cite this PDQ summary is:

PDQ® Integrative, Alternative, and Complementary Therapies Editorial Board. PDQ Cannabis and Cannabinoids. Bethesda, MD: National Cancer Institute. Updated . Available at: https://www.cancer.gov/about-cancer/treatment/cam/patient/cannabis-pdq. Accessed . [PMID: 26389314]

Images in this summary are used with permission of the author(s), artist, and/or publisher for use in the PDQ summaries only. If you want to use an image from a PDQ summary and you are not using the whole summary, you must get permission from the owner. It cannot be given by the National Cancer Institute. Information about using the images in this summary, along with many other images related to cancer can be found in Visuals Online. Visuals Online is a collection of more than 3,000 scientific images.

Disclaimer

The information in these summaries should not be used to make decisions about insurance reimbursement. More information on insurance coverage is available on Cancer.gov on the Managing Cancer Care page.

Contact Us

More information about contacting us or receiving help with the Cancer.gov website can be found on our Contact Us for Help page. Questions can also be submitted to Cancer.gov through the website’s E-mail Us.

General CAM Information

Complementary and alternative medicine (CAM)—also called integrative medicine—includes a broad range of healing philosophies, approaches, and therapies. A therapy is generally called complementary when it is used in addition to conventional treatments; it is often called alternative when it is used instead of conventional treatment. (Conventional treatments are those that are widely accepted and practiced by the mainstream medical community.) Depending on how they are used, some therapies can be considered either complementary or alternative. Complementary and alternative therapies are used in an effort to prevent illness, reduce stress, prevent or reduce side effects and symptoms, or control or cure disease.

Unlike conventional treatments for cancer, complementary and alternative therapies are often not covered by insurance companies. Patients should check with their insurance provider to find out about coverage for complementary and alternative therapies.

Cancer patients considering complementary and alternative therapies should discuss this decision with their doctor, nurse, or pharmacist as they would any type of treatment. Some complementary and alternative therapies may affect their standard treatment or may be harmful when used with conventional treatment.

Evaluation of CAM Therapies

It is important that the same scientific methods used to test conventional therapies are used to test CAM therapies. The National Cancer Institute and the National Center for Complementary and Integrative Health (NCCIH) are sponsoring a number of clinical trials (research studies) at medical centers to test CAM therapies for use in cancer.

Conventional approaches to cancer treatment have generally been studied for safety and effectiveness through a scientific process that includes clinical trials with large numbers of patients. Less is known about the safety and effectiveness of complementary and alternative methods. Few CAM therapies have been tested using demanding scientific methods. A small number of CAM therapies that were thought to be purely alternative approaches are now being used in cancer treatment—not as cures, but as complementary therapies that may help patients feel better and recover faster. One example is acupuncture. According to a panel of experts at a National Institutes of Health (NIH) meeting in November 1997, acupuncture has been found to help control nausea and vomiting caused by chemotherapy and pain related to surgery. However, some approaches, such as the use of laetrile, have been studied and found not to work and to possibly cause harm.

The NCI Best Case Series Program which was started in 1991, is one way CAM approaches that are being used in practice are being studied. The program is overseen by the NCI’s Office of Cancer Complementary and Alternative Medicine (OCCAM). Health care professionals who offer alternative cancer therapies submit their patients’ medical records and related materials to OCCAM. OCCAM carefully reviews these materials to see if any seem worth further research.

Questions to Ask Your Health Care Provider About CAM

When considering complementary and alternative therapies, patients should ask their health care provider the following questions:

  • What side effects can be expected?
  • What are the risks related to this therapy?
  • What benefits can be expected from this therapy?
  • Do the known benefits outweigh the risks?
  • Will the therapy affect conventional treatment?
  • Is this therapy part of a clinical trial?
  • If so, who is the sponsor of the trial?
  • Will the therapy be covered by health insurance?

To Learn More About CAM

National Center for Complementary and Integrative Health (NCCIH)

The National Center for Complementary and Integrative Health (NCCIH) at the National Institutes of Health (NIH) facilitates research and evaluation of complementary and alternative practices, and provides information about a variety of approaches to health professionals and the public.

  • NCCIH Clearinghouse
  • Post Office Box 7923 Gaithersburg, MD 20898–7923
  • Telephone: 1-888-644-6226 (toll free)
  • TTY (for deaf and hard of hearing callers): 1-866-464-3615
  • E-mail: [email protected]
  • Website: https://nccih.nih.gov

CAM on PubMed

NCCIH and the NIH National Library of Medicine (NLM) jointly developed CAM on PubMed, a free and easy-to-use search tool for finding CAM-related journal citations. As a subset of the NLM’s PubMed bibliographic database, CAM on PubMed features more than 230,000 references and abstracts for CAM-related articles from scientific journals. This database also provides links to the websites of over 1,800 journals, allowing users to view full-text articles. (A subscription or other fee may be required to access full-text articles.)

Office of Cancer Complementary and Alternative Medicine

The NCI Office of Cancer Complementary and Alternative Medicine (OCCAM) coordinates the activities of the NCI in the area of complementary and alternative medicine (CAM). OCCAM supports CAM cancer research and provides information about cancer-related CAM to health providers and the general public via the NCI website.

National Cancer Institute (NCI) Cancer Information Service

U.S. residents may call the Cancer Information Service (CIS), NCI’s contact center, toll free at 1-800-4-CANCER (1-800-422-6237) Monday through Friday from 9:00 am to 9:00 pm. A trained Cancer Information Specialist is available to answer your questions.

Food and Drug Administration

The Food and Drug Administration (FDA) regulates drugs and medical devices to ensure that they are safe and effective.

  • Food and Drug Administration
  • 10903 New Hampshire Avenue
  • Silver Spring, MD 20993
  • Telephone: 1-888-463-6332 (toll free)
  • Website: http://www.fda.gov

Federal Trade Commission

The Federal Trade Commission (FTC) enforces consumer protection laws. Publications available from the FTC include:

  • Who Cares: Sources of Information About Health Care Products and Services
  • Fraudulent Health Claims: Don’t Be Fooled
  • Consumer Response Center
  • Federal Trade Commission
  • 600 Pennsylvania Avenue, NW
  • Washington, DC 20580
  • Telephone: 1-877-FTC-HELP (1-877-382-4357) (toll free)
  • TTY (for deaf and hard of hearing callers): 202-326-2502
  • Website: http://www.ftc.gov
  • Updated: February 18, 2022

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