Marijuana cures cancer? Scientific research says probably not

Subjectively, one the wilder claims one can find on social media is that marijuana cures cancer. Or cannabis prevents cancer. It doesn’t matter what form – smoked, eaten, hemp oil (which is manufactured from the seeds of cannabis plants that don’t contain much THC, or tetrahydrocannabinol, the active hallucinogenic agent of cannabis) – some advocates for cannabis will try to make the argument that it is some miracle drug for cancer.

But is it? Yes, there are systematic reviews that indicate that cannabis may be effective in reducing nausea and vomiting in chemotherapy. But research has generated negative results in some well done clinical trials and some positive results in others. But that has nothing to do with actually curing or preventing the cancer itself, just dealing with the effects of the treatment.

So what has real research said about “marijuana cures cancer?” Well, not to give away the conclusion, but not very much. Let’s take a look.


About cancer

Let’s start this discussion by talking about cancer. Simply put, it is a group of diseases that involves uncontrolled or  abnormal cell growth with the potential to invade or spread to other parts of the body. Cancer starts when the genes of one or more cells mutate or change such that the these cells grow too quickly and too much.

Cancer usually takes numerous, sometimes up to 10, independent mutations in a population of cells before it can become a growing, metastatic cancer. Each mutation is selected, as in natural selection, because it provides some benefit to the cancer cell, such as the ability to cause blood vessels to supply the cells for nutrition and oxygen, the ability to divide rapidly, or whatever ability gives the cancer cells an advantage over normal cells. The mutations may arise randomly or can be caused by some environmental challenge, such as smoking and lung cancer.

One of the great myths about the disease is that it is only one disease. In fact, there are from 100 to over 200 different types of cancer in humans, with the actual number depending on how some researchers categorize some cancer types.. And each of these different cancers have different causes, different pathophysiologies, different genetics, different prognoses, and different treatments. So, there probably will never be one cure to cure them all. If cannabis, or more specifically some component of marijuana, has some effect on cancer, it may only be one or two cancers, not all of them.

On the other hand, there is a list of a few things you can do to prevent cancer, and smoking cannabis isn’t on that list. Remember, your body contains 35-45 trillion cells – even if your cells were 99.999% perfect, that would leave hundreds of millions of cells that have potential mutations that lead to cancer. It would be ridiculous, all research aside about marijuana and cancer, to believe that anything would make your body 100% resistant to mutations in all of those trillions of cells in your body.

Marijuana cures cancer – scientific research

If I could give one piece of above aver advice, it is to always be skeptical when someone makes some claim that some miracle pill or food will prevent or destroy cancer. There is no secret miracle drug out there, because, as we mentioned above, there are hundreds of cancers and trillions of opportunities for cancer to arise in your body. People want to push a narrative that a magic pill for cancer exists, or that Big Pharma is hiding that magic pill to make money off of chemotherapy, but that ignores basic scientific facts about cancer.

The first step I take before I investigate any internet claim is check if there are systematic reviews of randomized clinical research to find the best information for evidence based medicine. Systematic, or meta-reviews, are at the top of the hierarchy of biomedical scientific evidence. So, if someone is going to make a claim that marijuana cures cancer, or even one cancer, a proper scientific skeptic will try to find the highest quality evidence to support that claim

Therefore, I did a search of the Cochrane Reviews, one of the best sources of systematic reviews in clinical medicine, to find if there’s anything out there that establishes that marijuana cures cancer. My search showed that there was not one systematic review of THC or cannabis in cancer therapies (although several in some neurological issues, about which I wrote elsewhere). There are may be many reasons why Cochrane may not have a review on marijuana and any cancer, but mainly it’s because there just aren’t enough studies of high enough quality to roll up into a systematic review. That’s a clue, but it’s more a lack of evidence rather than solid evidence that cannabis has no effect on cancer.

We can look at cancer research in another way – there are currently over 8000 clinical trials that are recruiting patients for anti-cancer drugs (and over 19000 that are closed to patients). Cannabis research is a tiny speck in the body of work analyzing compounds that may have an effect on cancer.

Another myth about cancer is that researchers throw random compounds at cancer cells, and then they determine if it works or not. In fact, cancer research is a logical process to ascertain if a specific compound has a reasonable chance of inhibiting some part of the cancer growth or development. There may be some potential for an ingredient of marijuana to have some effect on cancer, but it probably doesn’t compare to the other 27,000 compounds in current clinical research, and, in a business sense, the return on investment for researching compounds that have better understood pharmacologic mechanisms of action are higher.

And then we have to understand the reality of cancer research. It’s important to understand that only a tiny percentage of therapeutic cancer drugs make it from an animal study clinical trial (about 5%), and even then, less than 10%  of oncology drugs that enter clinical trials actually end up being approved bye the FDA for use in humans. In other words, there’s only a 0.4% chance of any drug that’s being tested on cells or mice is ever going to end up being approved for human use. There is no nefarious conspiracy going on to block these drugs, it’s that in clinical trials the vast majority of these compounds fail to show effectiveness beyond their safety issues.

Thus, if you read of a study in mice or cells that seems to indicate that “marijuana cures cancer,” remember, the chances that that study will end up being clinically relevant is vanishingly small. There are just too many stories where a big medical advancement is touted in the press, but it vanishes from the radar.

And one more thing. We cannot play the argument from ignorance, that is, just because we haven’t shown that marijuana cures cancer, then it’s possible. If there isn’t any evidence that cannabis cures a particular cancer, then that means there’s no evidence. I’m not going to think “oh, they just haven’t tested it on THAT cancer, so how can you not be sure that pot doesn’t cure THAT cancer.” I also don’t have evidence there’s a pink unicorn walking on Mars, so I’m going to stick with a conclusion that there aren’t pink unicorns walking on Mars until such time evidence is brought to my attention.

Some claims about marijuana cures cancer

Let’s examine some of the more recent claims. Remember, if some article was published 10 years ago, and there’s not one single follow-up study, it’s a dead end, meaning that no one was able to repeat the data, and it’s probably not a viable treatment. Again, there are lots of research that can never make the jump from pre-clinical, that is, cell-culture or animals, to clinical research. But that’s how science works, ask a question, and find the evidence that answers that question.

In cancer research, failure is the norm. Here are some recent studies:

  • Cannabinoids: A new hope for breast cancer. “This review summarizes our current knowledge on the anti-tumor potential of cannabinoids in breast cancer, which suggests that cannabinoid-based medicines may be useful for the treatment of most breast tumor subtypes.” Now, you might think that smoking a joint is going to cure breast cancer. No, it won’t. The initial studies are done in cell culture, not in human clinical trials. Furthermore, the active ingredient must be delivered in the correct dosage over the correct amount of time at the actual tumor site to cause death of the cancer cells. This type of research will take years, even if it is successful. Smoking or consuming pot would never produce a THC level high enough at the breast cancer site to kill the cancer death. In fact, to do so might be harmful to the patient, so, as they say, don’t try this at home.
  • Chemopreventive effect of the non-psychotropic phytocannabinoid cannabidiol on experimental colon cancer. The authors concluded that cannabidiol, a non psychotropic ingredient of cannabis, can exert a chemopreventive effect on colon cells in cell culture. But once again, this has been not been clinically established in humans, and it has not been shown whether there is a dose response between the cancer and the drug. So, eating a bunch of cannabis is not going to prevent or cure colon, and the amount necessary to match the cell culture levels would probably be toxic to the patient.
  • Hash Oil for Gliomas? What Would You Do? I mentioned this above, but in another study, the authors found little credible evidence that hash oil, made from marijuana seeds, had any effect on gliomas. However, there are studies that showed spontaneous regression of gliomas in, what was claimed, response to the hash oil. This would be interesting information, except spontaneous regression of gliomas is not unknown, and is, in fact, fairly common. There was some preliminary evidence that it might work, but hardly a broad based clinical trial that would indicate an oncologist should use hash oil as his first, second, third, fourth or fifth line of treatment for a glioma. As the Harriet Hall stated in the article, “I didn’t find anything I would call “earth-shattering” or even anything that could be considered credible evidence that hash oil can cure advanced gliomas.”
  • Cannabis and cannaboids anti-tumor effects from the National Cancer Institute. There might appear to be a lot of research into cannabis using cell culture and animal models, but none have been transferred over to human clinical trials. This is not unusual, because even though it seems that there is a lot of research into cannabis and cancer, the total mass of research into other compounds with respect to cancer is substantially larger, because the evidence for both mechanisms of the treatment and clinical successes for these other products are much higher.
  • As of today, there has been only one clinical trial anywhere in the world that attempted to show an effect of any cannabis or cannabis products on cancer. It was a Phase I clinical trial, published six years ago, and has not gone any further. A review of PubMed and show no other clinical trials underway studying cannabis on any type of cancers.
  • A four year old study/editorial published in a top journal concluded that “cannabis-like compounds offer therapeutic potential for the treatment of breast, prostate and bone cancer in patients. Further basic research on anti-cancer properties of cannabinoids as well as clinical trials of cannabinoid therapeutic efficacy in breast, prostate and bone cancer is therefore warranted.” Now, their conclusion was based on preliminary evidence in vivo and in vitro studies, not randomized human clinical trials. Moreover, I cannot find any publication over the past four years that seem to support the ideas proposed by this study. It seems to be another dead end.
  • Recently, the National Academy of Sciences, Engineering, and Medicine published a 400 page review of health effects of marijuana, examining a wide range of potential claims for cannabis. They specifically looked at its effects on cancer, and found “no or insufficient” evidence to support marijuana’s use in preventing or treating any cancer, including gliomas, which make up 80% of malignant brain tumors. Of all cancers, marijuana has actually been used to treat gliomas in clinical studies, and no effect was ever found.

Marijuana cures cancer – simple math

Let’s say that we actually can gather evidence that marijuana has an effect on breast cancer. First, we need to determine how much THC actually would kill most breast cancer cells. In one study, the researchers determined that it would take a concentration of cannabinoids of approximately 10 µmol/L to cause the death breast cancer cells in cell culture.

This converts to around 3.14mg/L of THC. So, you’d have to assume that to kill any breast cancer cells, you’d need at least a blood level of 3.14 mg/L to cause breast cancer cell death.

So how close to that 3.14 mg/L can we get by just smoking a joint or two? According to research, smoking one cigarette will give you a blood level of THC of around 1.3-6.4 ng/mL serum, or about .00013-.00064 mg/L. In other words, to get the anti-cancer effect that is described in the breast cancer study, you would need to light up around 1000 marijuana cigarettes per day.

Yes, you would need to smoke over 1000 cannabis joints every single day until every single breast cancer cell would die. Of course, your lungs couldn’t tolerate that, nor probably your ability to function in any “normal” manner.

Of course, you could consume this in other ways, for example ingesting it, but again, you’d need to eat more than the equivalent of 1000 joints (because less digestion is less efficient in absorbing THC than the lungs, which is why it is smoked). And these levels may be more generally toxic to body, in effect killing you before it ever had any effect on the cancer itself. If we ever uncover clinical evidence that marijuana “cures” breast cancer, Big Pharma will spend the money researching which molecule is actually responsible for killing the cancer cell, the overall toxic dose where the cannabis (or active ingredient) which harms the body more than cancer cells, the amount necessary to kill the cancer cells, and how to deliver it effectively to the breast cancer cell.

And yes, Big Pharma will patent it, because they did all the hard work, and they will get $10,000 a dose (just a guess). So, let’s be clear. Smoking a couple of joints is NOT going to cure or prevent breast cancer.

marijuana cures cancer
Irrelevant. Unless you are a patent attorney trying to protect all potential medications without knowing if it really works or not.

Big Pharma and cannabis

I have heard the arguments that Big Pharma, the FDA, the National Cancer Institute (if the cannabis supporters even know it exists), and the US Government suppress all the research that show how great cannabis is for cancer because those groups don’t want marijuana to be legal. As amusing as that ad hominem argument might be (and it’s a fairly amusing one), if cannabis or any of its components actually could show efficacy against any of the 200 or so cancers, Big Pharma would be all over it.

Big Pharma would not be selling individual cannabis cigarettes, they would be isolating the active ingredient from the plant (or parts of the plant), determining the exact dose that would have an exact effect, determining how to deliver precisely to the cancer site, funding clinical trials, filing documentation with the FDA, then getting it into physician’s hands.

This is not an easy process (notwithstanding the $1 billion investment for the whole process), but it would probably be a profitable one if it worked. Big Pharma and the National Cancer Institute are looking at everything to treat all 200 cancers, and they ignore nothing for potential. If cannabis works (and it might), they will be all over it. Big Pharma is providing a lot of the funding for it.

In the meme above, there is an outlandish claim that there is a secret patent that proves that Big Pharma knows marijuana cures cancer. This is ridiculous on many different levels. First, patents are not scientific evidence. A patent can make any number of claims, and they don’t have to be proven, just possible. Is it possible that cannabis cures cancer? Sure, but there is no evidence that it can. Furthermore, a patent such as this one allows the patent holder to protect against future competitors. Let’s say a pharmaceutical company discovers that one component of marijuana, say cannabidiol, can treat a liver cancer. A patent like this one allows the patent holder to get royalties from the specific drug that does one specific thing, treat liver cancer.

Looking at the patent specifically, US20130059018, the quote in the meme is not a “claim,” a very specific legal term which means that the patent holder states that X can do Y, it is merely general background material for the patent. The very first actual claim of the patent states that:

A method of treating a patient comprising administering a therapeutically effective amount of a cannabis plant extract comprising a phytocannabinoid containing component and a non-phytocannabinoid containing component, wherein the phytocannabinoid containing component comprises at least 50% (w/w) of the cannabis plant extract and in which the principle is not tetrahydrocannabinol (THC) or cannabidiol (CBD), and the non-phytocannabinoid containing component comprises at least 15% (w/w) of the cannabis plant extract and further comprises a monoterpene fraction comprising a principle monoterpene which is selected from myrcenes or pinenes and a sesquiterpene fraction comprising a principle sesquiterpene which is selected from caryophyllenes or humulenes to the patient.

That’s very specific scientific verbiage explaining what needs to be done to get a potentially viable drug. It absolutely does not say, “smoke weed, cure cancer.” And it goes to my point that any possible treatment modality that arises from marijuana will be exceedingly complex. And very expensive.


Conclusion, the TL;DR version

Thus, is there any evidence that marijuana cures cancer? Or prevents cancer? Not at this time. Yes, there is some very early pre-clinical evidence that some components of marijuana may have a positive effect on some types of cancer, but we’re decades from having robust evidence supporting such claims. And the reader must be aware of the fact that only a small percentage of drugs that enter pre-clinical studies ever become clinically useful.

And it’s also important to remind the reader that if marijuana does show promise, it will be for one, or a hand full of cancers. It will never cure all cancers, because that’s logically improbable if not impossible.

Maybe in time, cannabis will have its place in the armamentarium of anti-cancer drugs if the pre-clinical studies meet the standards of scientific research and are repeated. The science should also identify an appropriate mechanism and what the active ingredient might be. In time, if it can be shown in clinical trials and be approved by the FDA, then it can be important. But right now, it’s mostly mythical. There really isn’t much here, just some initial research, some of which seems “interesting.”

One last thing. If the goal is to make pot legal, because there’s a group that wants to smoke pot for recreational purposes, that’s fine. But to do it on the back of trying to prove that cannabis has some medical value that isn’t based on real science? That’s just going to make people dispute all of your claims.

There might appear to be a lot of research into cannabis using cell culture and animal models, but none have been transferred over to human clinical trials. This is not unusual, because even though it seems that there is a lot of research into cannabis and cancer, the total mass of research into other compounds with respect to cancer is substantially larger, because the evidence for both mechanisms of the treatment and clinical successes for these other products are much higher.

If we ever uncover clinical evidence that marijuana “cures” any of the 100-200 cancers, Big Pharma will spend a boatload of money researching which molecule in the marijuana plant is actually responsible for that effect. Then they will determine the overall toxicity of the compound, the amount necessary to kill the cancer cells, and how to deliver it effectively to the patient. And at that point, they will patent it, because they did all the hard work, and they will sell the drug on the market. And it’s not going to be in the form of a joint that you’ll smoke (the FDA hurdles for that would be unbelievable), it will be in a colorful pill that you take with water.

Right now, any claims that marijuana cures cancer is plain nonsense.


Key citations:

The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!