Does Cannabis Really Cause Heart Attacks And Strokes?

A new study is making the rounds claiming so, apparently.  And unlike most previous studies on the matter, this one was not only very large, but was also able to fully tease out the massive confounding factor of tobacco as well.  It was run on both a representative sample as well as re-run on the subset of never-tobacco users, and controlled for many other variables as well.  So what did it find?

Daily cannabis users had a 25% higher risk of heart attack and 42% higher risk for stroke compared with nonusers overall.  For never tobacco users who were used cannabis daily, the odds ratios were higher, but confidence intervals were also much wider as well.  As for nondaily users, the numbers were proportionally much lower relative to days used per month, with those using weekly or less having barely any statistically increased risk for either cardiovascular outcome relative to nonusers.

And to that we give a resounding....(yawn).

Now, we all know that correlation is not causation, and this was a cross-sectional study that could not possibly rule out every other explanation for the association, nor determine temporality of the association.  And given how in all of the analyses of the study, the odds ratios were either 1) below 2.0, 2) had fairly wide confidence intervals, or 3) both, it is possible that the results were still at least partly (if not entirely) due to selection bias, reporting bias, or residual or unmeasured confounding, if not chance.  For example, while tobacco (which increased risk), alcohol (which appeared to decrease risk), and a host of individual health and demographic variables were statistically controlled for, the use or abuse of any other psychoactive substances (licit or illicit) was NOT controlled for, nor were any dietary factors.

And of course, as the study was done on BRFSS survey data, another major limitation was that it, by definition, only measured cardiovascular outcomes among those who lived to tell about it.  While longitudinal cohort studies in the past generally did not find any robust and significant differences in all-cause death rates between cannabis users in general versus nonusers, unlike in the infamous case of tobacco which has been well-known for decades.

In fact, interestingly enough, when the sample was restricted to those who never used tobacco, while daily cannabis users still fared worse, the lowest (best) point estimates for each of the cardiovascular outcomes studied were actually found among the nondaily cannabis users, not the nonusers, in the unadjusted results. And of course, that nuance was glossed over and only mentioned briefly.

That said, regardless, as a wise man once said, I have still never met a daily (or near-daily) cannabis user that could not benefit from cutting back a bit.  In other words, something about Aristotle and moderation comes to mind.  Food for thought indeed. 

UPDATE:  Another recent study, from Canada in 2023, also found a statistically significant and dose-dependent correlation between the severity of cannabis use disorder (i.e. abuse and/or dependence) and various cardiovascular disease outcomes.  But of course, the majority of cannabis users do not develop cannabis use disorders, let alone  severe ones.  And the study did not control for confounding from tobacco use either, so no causal relationship could be proven.  Either way, both studies lend themselves far more to a commonsense message of moderation, NOT the usual unscientific "no safe level" hysterics.

UPDATE 2:  One confounder that is difficult to fully measure and account for statistically is STRESS, which is a real killer when it becomes chronic.  And since one of the reasons why people use cannabis is to relieve stress, well, there is the biggest confounder right there.  Our verdict?  Cannabis is most likely no worse in this regard than, and probably less deadly than, the caffeine in coffee, tea, and elsewhere, which is about as legal and unrestricted as one can get.