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Home » Does marijuana cure cancer? Robust scientific evidence is lacking

Does marijuana cure cancer? Robust scientific evidence is lacking

Subjectively, one of the wilder claims one can find on social media is that marijuana can cure 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 cancer itself, just dealing with the effects of the treatment.

Furthermore, a 2022 systematic review (again, the pinnacle of the hierarchy of biomedical research) showed that “evidence from RCTs (randomized clinical trials) that medicinal cannabis increases appetite in people with cancer is limited.

However, this article isn’t about appetite or nausea related to cancer, it’s about whether cannabis can cure or treat cancer.

So what has real clinical and scientific research said about whether marijuana can cure cancer? Well, not to give away the conclusion, but not very much. Let’s take a look.

Cancer primer

Cancer is a group of diseases characterized by abnormal cell growth which can invade or metastasize to other tissues and organs. Although people use tumors and cancer interchangeably, not all tumors are cancer. There are benign tumors that do not metastasize and are not cancers.

The National Cancer Institute claims that there are over 100 types of cancer.  Cancer Research UK states that there are over 200 types of cancer.  The American Cancer Society lists over 70 types of cancer (although some are more classes of cancer rather than a single type).  Wikipedia lists over 180 different cancers.

The variance in the number of cancers results from the lack of precise definitions for some cancers. So researchers may group several different cancers into one heading. But clearly, there are up to 200 or more different cancers. There are even some arguments that state that there may be over 1000 different cancers, but for this article, we will stick with “200 or more.”

Furthermore, each of these cancers has a different etiology (cause), pathophysiology (development), treatment, and prognosis. When someone is called a “cancer researcher,” they are rarely studying all cancers, but they’re studying one small part of the story of one of the 200 or so cancers.

And unless we are missing some very fundamental aspect of cancer biology, there never will be one cure to cure all cancers. We will be looking for thousands of different cures for hundreds of different cancers. When someone says that they know of one cure to cure them all, I have all the evidence I need to call them a quack.

Cancer usually requires numerous, up to 10, independent genetic 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 causing blood vessels to supply the cells with nutrition and oxygen, or the ability to divide rapidly, whatever the feature is.

A recent study published in the journal Science makes a strong case for a random chance as the most important factor in cancer development. According to the study, the vast majority of cancers are just a simple error in DNA replication. If this is so, developing one of the 200 (or more) different cancers may be unavoidable, despite a “healthy lifestyle” or attempting to “boost” your immune system.

Geneticist Bert Vogelstein and mathematician Cristian Tomasetti, at the Johns Hopkins Sidney Kimmel Comprehensive Cancer Center, conducted the study, a follow-up to an earlier one, which arrived at the same conclusion. The researchers wanted to know whether replication errors were behind most cancers, versus other factors, such as tobacco.

The researchers found, after examining 32 different kinds of cancer, that 66% of these cancers were a result of chance mutations in cells, 29% resulted from the environment, and 5% from inheriting a mutation. If you think about the fact that the average human body contains about 50 trillion cells and that the mutation rate can be between 1 in 100 to 1 in 100 million nucleotides in humans, there can be millions of cells in the body that have some form of mutation that can lead to cancer. 

These mutations aren’t “naturally” a part of the cell’s physiology. Moreover, these mutations can have a lot of different causes – environmental (like smoking or UV radiation), viral (hepatitis B and human papillomavirus are the most famous), heredity, and maybe other things. These mutations are more or less random, and they can’t be prevented by anything special–if only it were that easy.

There are a few things you can do to prevent cancer, such as quitting smoking, staying out of the sun, getting your hepatitis B and HPV vaccinations, not drinking alcohol, keeping a low body weight, and eating a balanced diet. But even if you are a paragon of healthy living, a random mutation in some cells in your body can lead to cancer.

One last thing. A lot of our ideas about what may or may not cure cancer are based on preclinical research, which very rarely is brought into clinical trials or is successful in clinical trials. There seems to be a lot of evidence that it is difficult, if not impossible, to repeat the preclinical studies, so it makes it difficult, if not impossible, to accept the results from them. Simply, a lot of research that is publicly touted often ends up meaning nothing.

Oh, one more thing. Big Pharma isn’t hiding a secret cure for “cancer.” But they have brought the world thousands of effective treatments, in combination with evidence-based oncology, that has led to a substantial reduction in the cancer mortality rate over the past two decades.

Photo by Angiola Harry on Unsplash

Scientific research on cancer

If I could give one piece of above-average 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 there is a magic cure for all cancer, but that belief ignores basic scientific facts about cancer.

The first step I take before I investigate any internet claim is to 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 claim that marijuana can cure cancer or even one cancer, a proper scientific skeptic will try to find the highest quality evidence to support that claim

Therefore, I searched for 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 can cure or treat 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 may be many reasons why Cochrane does 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 does not affect 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 speck (and not a single one is to test effectiveness in treating any cancer) in the body of work analyzing compounds that may affect cancer.

Another myth about cancer is that researchers throw random compounds at cancer cells, and then they determine if it works or not. Cancer research is a logical process to ascertain if a specific compound has a reasonable chance of inhibiting some part of 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 to a clinical trial (about 1%). Even then, less than 13%  of oncology drugs that enter clinical trials end up being approved by 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 going to end up being approved for human use. There are no nefarious conspiracies among the FDA, CDC, Big Pharma, and the Illuminati attempting to suppress these drugs. It’s that the vast majority of clinical trials studying 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 can cure 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.

The only thing that is going to matter in my analysis is randomized, double-blind clinical trials that are published in real medical journals. A mouse study may be important in building knowledge, but it does not tell us whether cannabis or anything can treat or “cure” cancer.

And one last thing. We cannot play the argument from ignorance, that is, just because we haven’t shown that marijuana can cure cancer, then it’s still possible that marijuana can cure cancer. If there isn’t any evidence that cannabis can cure one 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 of such a pink unicorn walking on Mars is brought to my attention.

Photo by National Cancer Institute on Unsplash

Reviewing the science

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 is a lot 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 induce the death of those cancer cells. This type of research will take years, even if it is successful. Smoking or consuming pot would never produce a blood THC level high enough to kill those breast cancer cells without causing harm to all of the other cells in the body (see the next section where I discuss the pharmacology of using cannabis for cancer treatment).
  • 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 drug and colon cancer. So, eating a bunch of cannabis is not going to prevent or cure colon cancer, and the amount necessary to match what was used in cell culture would probably be toxic to the patient.
  • “Hash Oil for Gliomas? What Would You Do?” from our friends at Science-Based Medicine found little credible evidence that hash oil, made from marijuana seeds, had any effect on gliomas. However, some studies showed spontaneous regression of gliomas in, what was claimed, a 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 glioma. As 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 cannabinoids anti-tumor effects from the National Cancer Institute. There might appear to be a lot of research into cannabis treatments for cancer in cell culture or animal models – 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 concerning cancer is substantially larger. After all, 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 the 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 cancer.
  • A 2012 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 from in vivo and in vitro studies, not randomized human clinical trials. Further research published in 2022 showed in vitro evidence of an effect of cannabinoids on breast cancer cells, but again, this is not a clinical trial.
  • Recently, the prestigious National Academy of Sciences, Engineering, and Medicine published a 400-page review of the 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 been used to treat gliomas in clinical studies, and no beneficial effect was ever found.
  • Of course, there is strong evidence, presented in a large systematic review, that cannabis use is linked to testicular cancer.
marijuana cure cancer
Photo by Ahmed Zayan on Unsplash

Smoking 1000 joints every day

Let’s say that we actually can gather evidence that marijuana affects breast cancer. First, we need to determine how much active ingredient from cannabis (whatever that may be) 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 of 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 joint would 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 presumed anti-cancer effect that is described in the breast cancer study, you would need to light up around 1000 marijuana joints per day to achieve the blood level necessary to kill those breast cancer cells.

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 the body, in effect killing you before it ever had any effect on cancer itself.

You might think that if you got even a low level of cannabinoids in your blood, it’ll still kill some of the cells. That’s not how cancer therapy works. The dose-response of a chemotherapeutic agent like cannabinoids in this example, and do not kid yourself, this is chemotherapy, is adjusted to find the level that kills 100% of cancer cells. Even one left alive can cause a recurrence of cancer. Breast cancer is not a disease to be trivialized with ineffective therapies.

If we ever uncover clinical evidence that marijuana “can cure” breast cancer, Big Pharma will spend the money researching which molecule is 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. So, 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 works or not.

Big Pharma and marijuana

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 shows 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. Because despite the trope that Big Pharma is hiding some imaginary “cancer cure,” they actually would love to make a huge profit from a “cancer cure.” This doesn’t exist, but if we’re going to play this game, let’s be accurate.

As I mentioned above, Big Pharma would not be selling marijuana to cure cancer, 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, and 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 or more 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 that marijuana can cure 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 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 patent number 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 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.

Can marijuana cure cancer? No evidence

Thus, is there any evidence that marijuana can cure cancer? Or prevent it? 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 as a cure, it will be for one cancer, not every single cancer out there. 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 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 pseudoscience 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 concerning cancer is substantially larger. After all, 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 “can cure” any of the 100-200 cancers, Big Pharma will spend a boatload of money researching which molecule in the marijuana plant is 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 some highly researched form that allows the active ingredient to reach the target cell.

Right now, any claims that marijuana can cure cancer are plain nonsense.

Key citations:

Michael Simpson

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