Skip to content
Home » Medical uses of cannabis — a scientific review

Medical uses of cannabis — a scientific review

Last updated on February 7th, 2023 at 02:44 pm

I don’t know how we got to this point, but there are so many claims about the medical uses of cannabis, you would think it was the miracle drug of all time. Smoke some cannabis and suddenly everything from pain to cancer to neurological disorders disappear.

Since I don’t take medical claims lightly, and I always want to determine if there is good, solid clinical evidence, what is called science-based medicine, supporting these claims, I decided to dig into a few of them. And what I found is that either the evidence is lacking or that the evidence shows it doesn’t work. I’m not surprised.

I personally have no issue with smoking marijuana, since other “drugs”, like alcohol, are completely legal and socially acceptable. I think that the legalization of cannabis will reduce much of drug trafficking, reduce the burden of law enforcement and penal system costs, and have other beneficial effects for society.

But if you’re going to make wild claims about the medical benefits of cannabis, which don’t stand up to real scientific evidence, then I got to say “stop.” If you want to smoke cannabis because it relaxes you, fine, but if you’re going to get into my face with fake medical information, don’t be insulted if I laugh heartily.

This article will tackle a few of the most popular claims, but it won’t cover them all. Leave a comment if you want me to look into a medical claim about cannabis that I didn’t cover.

kush in close up photography
Photo by Alexander Grey on

The rules for examining the medical benefits of cannabis

So before I head down the road of whether cannabis has any effect on any particular disease or medical condition, I’m not going to play the argument from ignorance. If there isn’t any evidence that marijuana or THC cures particular cancers (or any disease), then that means there’s no evidence. It does not mean that it “could” work, it means we have no evidence that it works or not.

I don’t have evidence there are no pink unicorns walking on Mars, but I’m fairly certain of it. So don’t say “no one has ever researched smoking marijuana on brain cancer, so you don’t know if it does.” Nope, I don’t do those kinds of arguments. If there is no evidence that smoking cannabis cures brain cancer, we cannot claim that it cures brain cancer.

If I am certain that unicorns don’t exist, that there are no pink versions of unicorns, and that there’s not enough atmosphere on Mars to allow the survival of unicorns, then we have enough biological plausibility (or lack thereof) to state that there are no pink unicorns on Mars. Of course, someone will then state that there’s a secret cavern that is filled with oxygen and organic, GMO-free foods for a hidden population of pink unicorns. There’s no winning when it comes to the argument from ignorance.

The first step I take before I investigate any internet claim about medical uses of cannabis is to examine the quality of the evidence supporting the claim. Mostly, I want to find systematic reviews or meta-analyses of clinical and epidemiological research to give me the best possible evidence of whether a potential therapy has actual clinical usefulness.

A search of the Cochrane Reviews, which can be a useful tool in finding a scientific consensus on a new therapy, shows not one systematic review of THC or cannabis in cancer therapy, although there are some that look at mental disorders (which is still important). There are numerous reasons why Cochrane may not have a review about a procedure or drug, mainly because there just aren’t enough clinical 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 they are overwhelmed by solid evidence.

Let’s see what’s going on recently. Remember, if some article was published 10 years ago, and there’s not one single follow-up study, it’s dead on the vine, meaning that no one was able to repeat the data. No one was able to move it from some cell culture or animal model to a human clinical trial. This happens all of the time because failure in oncology drugs is the norm. Remember, if you find a study published in 1995, and it’s never cited or never repeated, that’s probably because it couldn’t be repeated. That’s how science works.

person holding green canabis
Photo by Aphiwat chuangchoem on

Anti-emetic for cancer patients

Cannabis has been used as an anti-emetic to ameliorate or mitigate nausea and vomiting after radiotherapy and chemotherapy in cancer treatment. In fact, marijuana has been smuggled into some cancer wards since the late 1930s. Unfortunately, even with this particular use of the drug, there have been negative results in some well-designed clinical trials and positive results in others. The highly variable result may result from difficult trial design to bias to a huge dose of the placebo effect, an effect that many scientists have concluded is overrated.

But even as an anti-emetic, marijuana has no curative power, it’s a palliative treatment for the nasty side effects of chemotherapy and radiotherapy in the treatment of cancer. Since weight loss and wasting are side effects of cancer treatments, any medication that can prevent nausea and vomiting can lead to better medical and lifestyle outcomes in cancer treatment.

If there is a real clinical difference between those who use cannabis vs. those who don’t for anti-emetic effects, we need real clinical trials that show the difference. Moreover, to do this type of clinical research correctly we require real dosage information, that is, at what dose do we get the best effect? Of course, this type of study would be difficult because it might be impossible to create a placebo that could be blinded for the participants and medical professionals.


I have written extensively about whether cannabis can be used for treating cancer. The vast majority of claims are not based on any substantial clinical trials. And by that, I mean a large (>2000 patients), randomized, double-blinded clinical trial with results published in a respected medical journal. If that kind of study showed that cannabis (or some active ingredient of it) worked, I’d be impressed.

Almost all cancer research with cannabis or cannabinoids is on cancer cell lines or rodent models. There is an old joke in scientific research circles is that we’ve cured cancer in mice 10,000 times! And the same joke has been made about cancer cell cultures. I can throw a cancer cell culture dish into the fireplace which will kill the cancer cells. But does that provide us with any information?

Furthermore, it’s important to understand that only a tiny percentage of therapeutic cancer drugs make it from an animal study to a clinical trial (less than 5%), and even then, only about 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.

A lot of the hype about cannabis being effective in treating cancer is based on these cell studies (and much fewer on animal studies), but as I have been known to say, “call me when phase 3 clinical trials are completed and the results published in a respected medical journal.” That’s because I know that very few drugs, especially for cancer ever show safety and effectiveness.

A lot of people say that if it works in cell culture, they will smoke a few joints of cannabis and that will prevent or even cure cancer. That’s not how it works.

Let’s say that we actually can gather evidence that marijuana has an effect on breast cancer for example. 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 of breast cancer cells in cell culture.

This converts to around 3.14 mg/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, you need to light up around 1000 joints per day. Yes, 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. On the other hand, you could consume this in other ways, for example ingesting it, but again, you’d need to eat more than 1000 brownies, assuming that each brownie has one joint worth of cannabis. You would probably need to consume more because digestion is less efficient in delivering cannabinoids to your blood than smoking it.

Moreover, these levels of cannabis are more generally toxic to the body, in effect killing you. 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 those breast cancer cells, the overall dose-response, 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. Smoking a couple of joints is NOT going to cure or prevent breast cancer.

Clinical trials

Clinical trials involving cannabis and cancer. There are currently over 93,000 clinical trials testing various compounds for the treatment of over 200 different cancers in humans. As far as I can tell, only five of the 77 studies involving cannabis are actually looking at the clinical effects of cannabinoids on cancers. And those studies are still recruiting patients, and it will take 10 years before we know if they were successful 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, insignificant speck of the cancer research world, compared to the vast body of research currently ongoing. 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.

I know that people love to cherry-pick data that confirms their beliefs, but that’s not how science works. Some of you might say that because there are five studies looking at cannabis and cancer, it must mean there’s something there. I beg to differ. Most of the money in research is invested in the 93,000 other clinical trials that have a better chance of providing the world with a cure for the disease.

I have heard the strawman arguments that Big Pharma, the FDA, the National Cancer Institute (if the cannabis supporters know it exists), and the US Government suppress all the research that show how great cannabis is for cancer and other medical indications because those groups don’t want pot to be legal. As amusing as that argument might be (and it’s a fairly bad 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 joints, they would be isolating the active ingredient, defining the exact dose, determining how to deliver it to the local cancer site in the body, funding clinical trials, filing documentation with the FDA, then getting it into the physician’s hands. This is not an easy process, but it would be a profitable one if it worked. Big Pharma and the National Cancer Institute are looking at everything, and they ignore nothing for potential in treating cancers. If cannabis, or some active ingredient in cannabis, works (and it might), they will be all over it. Big Pharma is providing a lot of funding to study the effect of cannabis on a wide range of medical conditions, including cancer.

Glioma and Rick Simpson hash oil

I’m not going to go through every cancer claim because I’ve written about it before. But there’s one that keeps showing up in spam, and that is the infamous Rick Simpson hash oil (and no, I’m not going to link to it, because of my policy of not linking to pseudoscience).

Internet grifters 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 in Science-Based Medicine, Harriett 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 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. And maybe those observations can be used to create a hypothesis that can be tested in a controlled clinical trial. But until that point, there is no evidence that hash oil works to treat glioma. None.

Neurological disorders

Let’s move on from cancer research to an area where cannabis might have some value that is supported by real medical research.

Dementia. As I’ve said before, the nearly gold standard of medical research are systematic reviews and meta-analyses, so I looked there for those that roll up the data from many clinical trials. And in this case, Cochrane concluded that cannabis doesn’t help. The authors concluded that “Based on data from four small, short, and heterogeneous placebo-controlled trials, we cannot be certain whether cannabinoids have any beneficial or harmful effects on dementia.” Again, the absence of evidence can be evidence of absence that cannabis having any effect on dementia.

Epilepsy. Another Cochrane Review examined the effect of smoking cannabis on epilepsy (an anecdote shared by Dr. Gupta). The authors found “no reliable conclusions can be drawn at present regarding the efficacy of cannabinoids as a treatment for epilepsy.” However, more recent systematic reviews seem to indicate that there might be positive effects of cannabidiol in treating some types of epilepsy.

Other neurological conditions. In a systematic review published in Neurologythe effect of marijuana was analyzed with respect to several neurological disorders and conditions. They included 34 clinical studies since 1948 (an extremely small number, because there aare just so few clinical studies), and looked at three different forms of cannabinoids–oral, THC, and synthetic. Here are their conclusions:

  • Spasticity, or chronic spasms of large muscles. All three forms showed some reduction in spasticity, though THC may take longer than a year to improve the condition.
  • Treatment of pain in multiple sclerosis. Most forms show a positive clinical effect, but THC probably has no effect.
  • Treatment of bladder dysfunction in multiple sclerosis. Nabiximols, a synthetic cannabinoid, seemed to work. The other forms of cannabis had no effect.
  • Treatment of tremors in multiple sclerosis. In this case, nabiximols have no effect, but other forms do.
  • Treatment of involuntary movements. Ineffective for Parkinson’s disease, and insufficient data for other forms, such as Tourette’s Syndrome.
  • Decrease seizures in epilepsy. There was insufficient data to support or refute its use.
  • Despite the incredibly small number of patients included in all of these trials, the authors found that more patients stopped using THC because of adverse effects (6.9%) vs placebo (2.2%).  Such a large dropout can bias the results of primary clinical trials and systematic reviews.
  • The placebo effect (reported to be as high as 70%) is a major impediment to determining whether cannabis has any effect on these neurological conditions. If there’s nothing more than a placebo effect, which is really no effect whatsoever, then the numerous, albeit minor, adverse events outweigh the benefits, and it should not be added to the body of literature regarding evidence-based medicine.

The tl;dr version

  • Marijuana prevents nausea in cancer treatment patients — maybe, maybe not. No solid research in the area.
  • Marijuana cures or prevents cancer — no clinical evidence that it does.
  • Marijuana can treat neurological conditions — there is some conflicting evidence that it might work.
  • There is no global Big Pharma conspiracy to suppress medical research on cannabis. If it could “cure” one cancer, they’d be all over it trying to find the right dose, delivery mechanism, and pretty advertising to make billions of dollars.

If you want to smoke marijuana (or eat it in a brownie — not sure that’s a thing anymore, it was when I was in college) because it’s relaxing, or you need to blow off steam after a tough day, fine. Go for it. I absolutely do not understand why this usage is illegal. It’s costly to society. And banning it provides no benefit to society.

On the other hand, I find most, if not all, of the medical claims made about cannabis to be laughable. The evidence is just so weak or non-existent, I actually have no clue why it’s part of the discourse, but then again people deny evolution, and we end up arguing that. Yes, there are bits and pieces of intriguing evidence that a component of marijuana may have some benefits to human health.

But we’re a long way from testing medical cannabis with real clinical trials, then getting it to market. And trust me, when someday we have found some real clinically significant uses, it’s not going to be sold as a “joint.” It’s going to be developed into some sort of medical delivery formulation (like a pill or injectable solution) that gets the purified pharmacologically relevant compound to the physiological site where it would work. That’s how real medical science works.

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.


  1. There is a US Patent that has, as one of its statements, “This invention relates to the use of phytocannabinoids, either in an isolated form or in the form of a botanical drug substance (BDS), as a prophylactic or in the treatment of cancer.” There are memes that state that Big Pharma knows that cannabinoids cure cancer or else they wouldn’t have patented it. However, patents do not represent peer-reviewed science and merely conjecture on the part of the patent holder, so that they may potentially block anyone from manufacturing the drug for the use that it claims. There is no evidence that this cannabinoid has any real potential of doing anything until such time that there are randomized clinical trials that support these claims. So, don’t mention patents. They mean absolutely nothing because drug companies continuously file patents when they even think something might do something. Most drug patents never end up being drugs.
  2. Let me remind you that the quality of the source used matters, and cherry-picking primary studies to support a confirmation bias is not how real skepticism works. Remember, if some article was published 10 years ago, and there’s not one single follow-up study, it’s dead on the vine, meaning that no one was able to repeat the data.
  3. Do not accuse me of cherry-picking. There are lots of published articles out there using THC or something else in mice or cells. That’s not clinical evidence, which is the gold standard. These models just tell us maybe it works. It never tells us that it does work.
  4. If you’re going to make a lame Big Pharma Shill Gambit to invent some claim that I, and my friends, are suppressing scientific knowledge about how valuable marijuana will be to “curing cancer.” Bring evidence, first by understanding what is cancer.


Michael Simpson

Don’t miss each new article!

We don’t spam! Read our privacy policy for more info.

Liked it? Take a second to support Michael Simpson on Patreon!
Become a patron at Patreon!