Is Cannabis Usage “Related” to Strokes?

Any research related to cannabis is bound to be sensationalized or politicized because people have strong emotional and political views about its usage. A few months ago, my fellow Scilogs blogger Suzi Gage wrote an excellent blog post about a study that investigated the link between cannabis usage and intelligence. That study had many critical flaws which were often ignored when the research was reported and discussed in the media. All research should be conducted and reported cautiously. However, when research touches on highly controversial topics, it is even more important that researchers clarify whether their research establishes statistically rigorous associations and true cause-effect relationships or whether they are merely pointing out important observations that require further research to derive definitive conclusions.

The recent paper entitled “Cannabis-related Stroke: Myth or Reality?” published by Wolff and colleagues in the journal Stroke investigates whether cannabis usage is related to stroke, concludes:


“In regard to the literature, cannabis-related stroke is not a myth, and a likely mechanism of stroke in most cannabis users is the presence of reversible MIS induced by this drug. The reality of the relationship between cannabis and stroke is, however, complex because other confounding factors have to be considered (ie, lifestyle and genetic factors). To confirm that cannabis may be a precipitating factor of RCVS with severe complications, an epidemiological study to determine the incidence of MIS, complicated or not by stroke, in the general population and in the cannabis users is necessary.”


The abbreviation MIS stands for multifocal intracranial stenosis, and refers to the presence of multiple blockages in the blood vessels of the brain that are impeding the blood flow and causing the stroke. RCVS stands for reversible cerebral vasoconstriction syndrome and describes a transient spasm of the blood vessels that briefly interrupts the blood flow to the brain, thus causing the stroke. The novelty of the paper by Wolff and colleagues is their idea that cannabis usage causes reversible MIS, i.e. that cannabis transiently causes multiple blockages that are reversed when cannabis is removed.

This is indeed an interesting idea, but unfortunately, they do not present any convincing data to back up this intriguing hypothesis. The data in their paper consists of a table listing 59 cases of stroke in patients who used cannabis, combining their own data with data that has been published by others. The authors admit that many of the patients who used cannabis were also active users of tobacco and alcohol, which makes it difficult to attribute the stroke to cannabis as opposed to these other confounding factors.

Most of the patients had some sort of brain imaging performed to diagnose the stroke, but less than half of them had a follow up scan later on to see if the blockage was still present. In those few cases where follow up imaging was performed, most of them did show some degree of reversibility of the blockages in the brain blood vessels. However, they do not present data on whether strokes in non-cannabis users also show similar reversibility patterns.

Wolff and colleagues also reference an older 2001 paper “Triggering Myocardial Infarction by Marijuana” by Mittleman et al and state that their current findings are in accordance with the conclusions of the 2001 paper. The paper by Mittleman and colleagues studied heart attacks and not strokes, but both diseases are caused by reduced blood flow, so it is not unreasonable to compare the data. The 2001 paper stated that the risk of having a heart attack is increased 4.8 fold within an hour of using cannabis. However, one has to bear in mind that the 2001 paper studied heart attacks in 3882 patients, of whom only 3.2% used cannabis and only 9 patients had used cannabis within an hour of the heart attack. The 4.8 fold risk determination was therefore based on this tiny sample of 9 patients!

In summary, the paper by Wolff and colleagues does not really answer the question of whether cannabis-related stroke is myth or reality. The small sample size, the observational nature of the data, the lack of follow up imaging on all the patients and the lack of controlling for confounding risk factors such as tobacco (which has a very strong association with stroke) make it difficult to draw definitive conclusions. All we can say is that Wolff and colleagues have presented an intriguing hypothesis that cannabis might cause strokes by inducing transient blockages or spasms of blood vessels in the brain. We need more definitive data to determine how cannabis usage is “related” to strokes: Is it a true cause of stroke or is it just an indicator of other more established risk factors, such as tobacco usage.

Wolff, V., Armspach, J., Lauer, V., Rouyer, O., Bataillard, M., Marescaux, C., & Geny, B. (2012). Cannabis-related Stroke: Myth or Reality? Stroke, 44 (2), 558-563 DOI: 10.1161/STROKEAHA.112.671347

11 thoughts on “Is Cannabis Usage “Related” to Strokes?

  1. Don’t forget, the threat of legal action against you can raise tension, which may increase the chance of certain medical problems occurring.

    Until you study people, lots of people, who are using cannabis legally and it has been long enough since they used it illegally (Colorado 2016 is a good place to start) to shed the residual stress of criminalisation, then the stress confound is too big to ignore.


  2. Sanja

    Hi! I have been google-ing a bit about correlation between marijuana usage and incidence of strokes and heart-attacks within the marijuana consuming population, so I’ve came across your article. However, I don’t quite understand, how it is possible for marijuana to cause vasospasms and vasoconstriction in general, when its effects are used in a completely paradox manner, and by that I mean as a part of the supportive therapy for glaucoma, aka as a vasodilator? I’m also keeping in mind that the effect is “limited” to terminal blood vessels (capillary, arterioles, etc), so I would really appreciate if you could find some time to clear this issue up for me, because I think this particular topic on your blog is one of the rare non-biased pages surrounding THC use I could find on the internet until now. Thank you!


    1. @Sanja

      The purpose of this blog post is to point out that there is significant controversy in this area and that people have observed both vasodilatory and vasoconstrictive effects. This can be due to a number of reasons, such as the use of different doses of cannabis, different durations of cannabis exposures (i.e. short-term versus long-term) or the simple fact that people have studied blood vessels in different organs. For example, it is already known that blood vessels in the lung have a different vasoconstrictive/vasodilatory response than blood vessels in other organs (this research on lung blood vessels was not performed in the context of cannabis).

      The second thing to keep in mind is that the paper I am referencing in my blog post tried to establish a link between stroke and cannabis usage and hypothesized that this was due to transient vasospasms or vasocontrictions, but they did not have very solid evidence for this. Strokes are not necessarily caused by vasospasms or vasocontrictions. In most cases, strokes are probably caused by small blood clots which obstruct the blood flow. If there were a clear causal link between cannabis usage and strokes, it could be related to effects of cannabis on blood clot formation, but the article did not provide any obvious proof for such a mechanism.


  3. Thankyou

    Cannabis is the only thing that helps my disorder without all the side effects, do you know any other articles describing the flaws of this study.


    1. Thanks for your comment. The field of research on cardiovascular complications of Cannabis is still evolving, and there are other studies which have shown cardiovascular problems with Cannabis. Here is a link to one of the most recent review articles:

      Adverse Cardiovascular, Cerebrovascular, and Peripheral Vascular Effects of Marijuana Inhalation: What Cardiologists Need to Know

      The article suggests that we need more research to understand the cardiovascular side effects of Cannabis, but that there is enough evidence to justify concerns about potential cardiovascular complications associated with Cannabis.


    1. The link you provided in your comment is a 2011 paper published by the same group of researchers. The 2011 study was a correlational study, i.e. the researchers found that 10 out of 48 young patients with a stroke used cannabis. I do not believe that such a correlation proves a true cause and effect relationship between cannabis usage and stroke.


  4. Thomas Barton

    I left a comment is the past, I personally think if cannabis did cause RVCS it would be from combustion, not the cannibinoids. We haven’t heard about stroke in Marinol/Sativex Patients. And the LD50 scores are very high with even smoked cannabis, I personally only use whole plant tinctures for my medical condition since CBD decreases Cardio Affects and Anxiety.


  5. Thomas Barton

    Also RCVS is associated with depression and migraines which are associated with endocannabinoid deficiency. Self Medicating it sounds like to me.


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