Part 2. Marijuana and cancer – assessing the science

This is Part 2 of a series of six articles discussing marijuana’s use in medicine and health care. In this part, we discuss marijuana and cancer – probably one of the most passionate and controversial “debates” associated with the use of cannabis.

It’s clear that there are numerous claims about the value of marijuana in preventing or treating various cancers. But what are facts? And what is smoke?

In this article, I’ll look at some of the more prominent claims, along with a skeptical analysis of those claims.

About cancer


Let’s start with cancer, subjectively one of the most claimed therapeutic uses of cannabis. There are 100 to over 200 different types of cancer (the actual number depends on how some researchers subdivide some cancer types) in humans. And each of these different cancers have different pathophysiologies, different genetics, different prognoses, different causes, and different treatments. In other words, it is not one unitary disease which might someday have one unified course of treatment. This is one of the biggest myths about cancer.

Cancer usually takes numerous, 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 causing blood vessels to supply the cells for nutrition and oxygen, or the ability to divide rapidly, whatever the feature is. They aren’t “naturally” a part of the cell, but are caused by a mutation. And 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, and smoking cannabis isn’t on that list. In fact, avoiding environmental toxins, such as smoking anything, might reduce the risk of cancers, so there’s that.

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Marijuana and cancer


For marijuana and cancer, we should review some of the better studies in marijuana research on cancer. Most of the cannabis and cancer research is primary–it has yet to be repeated widely, and there is little or no clinical evidence which can be used in systematic reviews of cannabis, which would form the basis of evidence based medicine of using cannabis in a clinical setting.

That being said, let’s take a look at some of the research:

  • Breast cancer. A recent review of the relevant research regarding the use of cannabinoids (the essential active compounds of marijuana) in the war on breast cancer concludes that “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.” All of this research is based on rodent studies, and the joke in scientific research circles is that we’ve cured cancer in mice for decades. (See note 1)
  • Breast cancer. Again. 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. The amount to actually have an effect on breast cancer cells would be toxic and impossible to consume.  Smoking a couple of joints is NOT going to cure your breast cancer. (See note 2)
  • Colon cancerIn a recent article, researchers examined the effect of cannabidiol, a non-psychotropic ingredient of cannabis, on chemically induced cancerous colon cells in cell culture. The authors concluded that it could prevent colon cancer. Now, if I was harsh about mouse research as being an indicator of clinical success, I’d be harsher about cell cultures. This was tested on chemically induced colon cancers, which may or may not have the same pathophysiology of in situ colon carcinomas. And once again, we lack any clinical evidence that it might work in humans, but I guess this is another bet into the 0.4% chance column.
  • Glioma. Junk medicine hawkers have been pushing hash oil to “cure” gliomas, a type of malignant brain and central nervous system cancer. It is based upon some preliminary research on just 9 patients in Spain. Only two of the patients survived more than a year, while the seven others had a course of the disease not different than what is experienced in typical treatments of gliomas. In fact, in the two patients who survived the longest (yet still died), the effect can be attributable to spontaneous (but temporary) regression of the disease, a fairly common event. In a review of these studies and claims, Dr. Harriet Hall stated, “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.” At this point, there is no supporting evidence that hash oil should be considered as the first, second, third, or fourth line of treatment for gliomas. Right now, we have observations (which are just barely above anecdotes on the scale of scientific evidence) that hash oil might work under the right conditions–but we have no real evidence that any of those suppositions are true. None.
  • Clinical trials involving cannabis and cancer. There are currently 8000 clinical trials that are recruiting patients for anti-cancer drugs (and over 19000 that are closed to patients), and as far as I can tell, there are none registered for marijuana, or isolated cannibinoids, dronabinol and nabilone.  On the website, which tracks every clinical trial registered across the world (and in case you’re going to ask, no one would have a real clinical trial and not register it, since it shows you have regulatory approval to begin a trial), there is precisely one cannibinoid being used to treat cancer, and that is Sativex, which is a patented drug of nabixomols isolated from the marijuana plant. This study is just a Phase 1 trial, it hasn’t recruited any patients, and is years from providing us with any meaningful results.
Irrelevant. Unless you are a patent attorney trying to protect all potential medications without knowing if it really works or not.
Irrelevant. Unless you are a patent attorney trying to protect all potential medications without knowing if it really works or not.

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.

Cannabis research is a tiny speck (though not an insignificant speck) of the cancer research world, compared to the vast body of research currently ongoing into thousands of other compounds. Cancer research isn’t randomly throwing compounds at cells and seeing if they work or not, it’s a logical process to determine if a compound has a reasonable chance of inhibiting some part of the cancer growth or development.

There is some potential for cannabis, but it probably doesn’t compare to what is currently in the 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 on cancer are higher.

If we ever uncover clinical evidence that marijuana “cures” breast cancer, Big Pharma will spend the money researching which molecule is actually responsible, the over all toxic dose, the amount necessary to kill the cancer cells, and how to deliver it. And then they 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, there is ongoing active and robust research in the roles of marijuana (and it’s constituent chemicals) in preventing or treating cancer. However, it takes decades to move from preliminary data from animal or cell culture studies to clinical trials that become the basis of a new drug application. And we’re not there yet.

See the next article in this series, Part 3, Marijuana and neurological disorders – assessing the science.



  1. 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, only about  less than 8% (pdf) of oncology drugs that enter clinical trials actually end up being approved 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. And in cancer therapy, sometimes drugs that have a 51:49 benefit to risk ratio, and only keep a person alive for a few months get approved. So, the ones that don’t make are remarkably ineffective or unsafe. There is just no evidence that cannabis will treat or prevent breast cancer in humans. None. But let’s hope that it will fall in the 0.4% category.
  2. 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 achieve 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 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 an anti-cancer effect (for which there is no evidence at this time), you need to light up around 1000 joints per day. Yes every single day until every single breast cancer cell would die (again, no evidence that it can). 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 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.

Editor’s note: This article is a substantial update of an article that was originally published in April 2014. It has been completely revised and updated to include more comprehensive information, to improve readability and to add current research. I’ve also sub-divided into five separate articles to improve readability, and to allow a reader to choose the marijuana and medicine article that is of highest interest.

Another editor’s note: I have a policy of open commenting and dissent to my articles. I only delete spam, racism, and just random nonsense. Please comment here if you wish, because I know everyone has an opinion on marijuana. But ad hominem hatred, strawman arguments and other logical fallacies will be mocked–bring high quality, peer-reviewed evidence. I might even rewrite or add another section if it’s high quality and peer-reviewed.

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!

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  • Chris Klok

    I’m Chris Klok, Video Productions at Marana High School. My wife had breast cancer which was already in the stage IV and the doctor said we needed a miracle for her to be cured of the cancer. But for grace over my family a miracle happened when we learnt about Rick Simpson Cannabis Oil, she has been on the treatment for the past 3 months and the result was tremendous as the Hemp Oil has cured the Cancer. If you have any cancer problem, chronic diseases, diabetes or any related dangerous diseases, please contact Dr. George Jones via:

    Chris Klok

  • Niël Kruger

    Don’t know if you already know of these scientific based websites, but they also provide very insightful information regarding cannabis as medicine and about cannabis to treat cancer:

  • Niël Kruger

    SR, you are focusing on the smoking of cannabis as a way to administer the THC and CBD to fight the cancer cells. The whole cannabis cures cancer crowd doesn’t advocate the smoking of cannabis to cure cancer but they advocate the use of what they call cannabis oil, which is extracted from the plant to produce a liquid which has a high concentration of THC and CBD. Can you provide anything about their claims that the use of cannabis oil cures cancer or not?. You know as well as I do, the method of how a drug is administered, has an effect on how effective it is. Using cannabis oil due to its higher concentrations of THC will also make it a lot easier to reach the 3.14 mg/L of THC in the blood, or do you disagree?

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  • Ricky

    “The amount to actually have an effect on breast cancer cells would be
    toxic and impossible to consume. Smoking a couple of joints is NOT
    going to cure your breast cancer. (See note 2)”

    This is the sort of ridiculousness that tells me you are a prohibitionist. Do you think they had those mice smoking joints?

    Pot hater

    • IsaacLHawk

      GET A BEST TOP255-CAREER ::: @1md6.





    • Niël Kruger

      Ricky, your comments doesn’t add any value to the discussion at hand and doesn’t help your cause either! If you don’t have anything meaningful to ask or to add to the discussion, for example, scientific evidence which supports your argument, just STFU! Else, we both may learn quite a lot from these discussions!

      • Ricky

        STFU? No. I will say what I want until this prohibitionist kicks me off his pot hater board. Notice he had no reply to my comment?
        You are clearly the king of meaningful discussion.

        I happen to know plenty about cannabis. Enough to know that this site is meant for people like yourself. Do Enjoy it.

        • Niël Kruger

          If you know so much about cannabis, please enlighten us with all your knowledge. We are here to learn!

          • Ricky

            What do you want to know?

            • Niël Kruger

              I would like to know the A to Z about cannabis!

            • Ricky

              Kinda hard to fit in one post. Can you narrow it down a bit?

              Also, google is a great source for info. Pubmed is also excellent.

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