A new research letter looks at the differences between cannabis users (CU) and non-CU in stroke risks and outcomes among young (<45 year old) stroke patients.

The Daily Mail states that using cannabis increased the risk of stroke by narrowing the arteries in the head. Science in the Daily Mail is more often wrong than right and takes more than a grain of salt to make it palatable.

This article from WebMD points out that this kind of study cannot show causality. To do that, you would need to ensure that there were no other differences in the two groups of patients, aside from their cannabis use. In fact, there were major differences between the groups, the most troubling of which is the higher use of tobacco and alcohol in the cannabis use group.

Tobacco is known to be a major risk factor for stroke, so without correcting for this confounder, it is impossible to draw any causality from the study. The authors note that 2 of the CU patients were also cocaine users, another confounding risk factor.

The article found that those in the CU group were more likely to have a stroke resulting from arterial stenosis rather than from embolic disease. Tobacco is also linked to arterial stenosis, so it is unclear if this increase results from an increased exposure to cannabis vs an increased exposure to tobacco.

It does seem plausible that the use of cannabis can increase the risk of stroke, especially when one considers the known increased risk from synthetic cannabinoids. For most consumers of cannabis, the risk comes from combining cannabis with tobacco. The risk imparted by cannabis alone is relatively low, similar to the risk of environmental pollution. Public health measures to decrease the risk of stroke should direct cannabis users to avoid the co-use of tobacco and to use a vaporizer when possible.









