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Home » Part 3. Marijuana and neurological disorders – assessing the science

Part 3. Marijuana and neurological disorders – assessing the science

Last updated on September 14th, 2020 at 12:03 pm

This is Part 3  of a series of six articles discussing marijuana’s use in medicine and health care. In this part, we discuss marijuana and neurological disorders – probably the only field of study regarding medical uses of cannabis that has a robust area of clinical research.

Although research into the use of marijuana and cancer takes all the news these days, there is probably just as vigorous research into neurological disorders.  If you read the story regarding CNN’s chief medical correspondent, Dr. Sanjay Gupta, who claimed he changed his mind about marijuana, you’d know he was also convinced that marijuana had some great potential in mental health. But is there really any high quality evidence?

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

Sanjay Gupta’s conversion


Unless you were hiking in the Amazon River jungles, with no access to the internet or American TV, you probably have heard that CNN’s chief medical correspondent, Dr. Sanjay Gupta, changed his mind about marijuana (or “weed” as he keeps saying). Of course, this has become big news, because he’s such a “respected doctor” (why is that? Because he’s on TV?), and because a few years ago he was vociferously anti-cannabis.

I have no doubt that Dr. Gupta’s “conversion” to being pro-weed is genuine (and that his previous stance of anti-weed was similarly authentic), but we need to weed out what is real and what’s just smoke about his comments. His first major point about cannabis was that the United States Drug Enforcement Agency (DEA) considers marijuana to be a Schedule 1 drug, which is defined as “drugs with no currently accepted medical use and a high potential for abuse.”

Dr. Gupta thinks this classification is ridiculous, and on the surface, many people, even those who are not devoted pot smokers, would probably agree. This is actually a valid point–there are no valid reasons to maintain cannabis as a schedule 1 drug. It’s probably a relic of a different era when marijuana was considered a gateway to hard drugs (ludicrous) or corrupted our youth (we were all corrupted during our youth, and it had nothing to do with pot).

However, this is a political discussion, at least in the USA, and it is hardly a medical/scientific one. The chances of any political party having the fortitude to correct this classification is about as close to 0 as you can get, without actually stating that there is a 0% chance. But if Gupta wants to make a big deal of this, or that he’s so self-centered that he thinks he’ll change the mind of politicians, more power to him. But for me as a skeptic, it is not the most important thing he says.

In Dr. Gupta’s article, he mentions a young girl who “started having seizures soon after birth. By age 3, she was having 300 a week, despite being on seven different medications. Medical marijuana has calmed her brain, limiting her seizures to 2 or 3 per month.” This is simply an anecdote of no quality whatsoever. Did he thoroughly investigate her case to determine if the number of seizures actually went down? Do we know that cannabis has anything to do with the change?

Is this nothing more than a Post hoc ergo propter hoc fallacy? Just because she consumed cannabis and the seizures decreased does not mean anything about cannabis’ causative properties with regards to this type of seizure. And then, Dr. Gupta continues with the anecdotes by stating, “I have seen more patients like Charlotte first hand, spent time with them and come to the realization that it is irresponsible not to provide the best care we can as a medical community, care that could involve marijuana.” Why do these TV doctors (like Dr. Oz) think that their anecdotes are better than anyone else’s.

Anecdotes are useless because they aren’t controlled, because they are subject to all levels of bias, and because these stories aren’t peer-reviewed. In other words, anecdotes have no value in science-based medicine.

Anecdotes do have value in formulating testable scientific hypotheses, but assuming that anecdote equals data, and more anecdotes equals more data is simply pseudoscientific. I don’t care what Sanjay Gupta writes or says publicly–however, providing these stories as “evidence” that marijuana has a medical benefit is essential like telling me that he observed homeopathy (which is just water) curing cancer or treating the flu. It’s laughable.

Marijuana and neurological disorders


Ignoring Dr. Gupta’s well-intentioned reliance upon anecdotes and stories, what does the science say? What’s the best evidence out there to support marijuana and neurological disorders – is there anything?

The best answer is “maybe.”

  • Dementia. As I’ve said before, the nearly gold standard of medical research is the Cochrane Reviews (they are great, but not perfect) which attempt to roll-up numerous clinical trial into one overarching analysis of all of the studies, removing bias and poor design from the mix.  I looked there for systematic reviews regarding marijuana and dementia. And in this case, Cochrane concluded that cannabis doesn’t help. The authors concluded that “this review finds no evidence that cannabinoids are effective in the improvement of disturbed behaviour in dementia or in the treatment of other symptoms of dementia.”
  • EpilepsyAnother 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.” This means what it means–that a thorough systematic review of clinical research currently available on marijuana’s effects on epilepsy has shown nothing. Sure, maybe better trials will show it’s quite efficacious, but remember, that doesn’t mean it will be so. And physicians treating epilepsy need to stick with evidence based medicine.

Meta review


In a recent systematic review published in Neurologythe effect of marijuana was analyzed with respect to several neurological disorders and conditions. They included 34 clinical studies published since 1948 (an extremely small number, because there 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, although the Cochrane Review above says about the same thing in a different way.
  • 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 body of literature regarding evidence based medicine.



Another meta review


In a recent systematic review (once again, the most powerful clinical research tool available to real medicine), published in JAMA, examined randomized clinical trials of cannabinoids for the following indications: nausea and vomiting due to chemotherapy, appetite stimulation in HIV/AIDS, chronic pain, spasticity due to multiple sclerosis or paraplegia, depression, anxiety disorder, sleep disorder, psychosis, glaucoma, or Tourette syndrome.

The review did not examine marijuana and cancer, simply because of the paucity of randomized clinical trials with marijuana and cancer.

The systematic review included 79 separate clinical trials that had a patient population of 6462 patients. That’s a very nice sample size, though I’ve written about studies that included over 1 million patients.

Here’s what they found:

    • Most of the trials included in this study showed improvements in symptoms after use of cannabis. However, not all of these improvements were statistically significant.
    • Compared to placebos in randomized clinical trials, the average number of patients was greater in showing a complete nausea and vomiting response (improvement), greater reduction in pain assessment, or reduction in spasticity.
    • There was an increased risk of short-term adverse events (AEs) with cannabinoids, including serious AEs. Common AEs included dizziness, dry mouth, nausea, fatigue, somnolence, euphoria, vomiting, disorientation, drowsiness, confusion, loss of balance, and hallucination.

The authors concluded that:
[infobox icon=”quote-left”]There was moderate-quality evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity. There was low-quality evidence suggesting that cannabinoids were associated with improvements in nausea and vomiting due to chemotherapy, weight gain in HIV infection, sleep disorders, and Tourette syndrome. Cannabinoids were associated with an increased risk of short-term AEs.[/infobox]

In another clinical review published in JAMA, researchers examined the use of marijuana for chronic pain, neuropathic pain, and spasticity that resulted from multiple sclerosis. They found high quality evidence published in 18 trials that showed positive results for those indications.

These authors concluded that:

[infobox icon=”quote-left”]Medical marijuana is used to treat a host of indications, a few of which have evidence to support treatment with marijuana and many that do not. Physicians should educate patients about medical marijuana to ensure that it is used appropriately and that patients will benefit from its use.[/infobox]

These results are strongly supportive of the use of cannabis for a few narrow neurological issues, but are not strongly supportive of widely claimed indications such as palliative use in chemotherapy. This is important data can be the foundation of evidence based medicine with respect to marijuana and neurological disorders such as chronic pain.

See the next article in this series, Part 4, Marijuana and health risks – assessing the science.

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 six 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:

Michael Simpson

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