NIH-funded observational study shows risk grows sharply with more frequent use.

Frequent cannabis smoking may significantly increase a person’s risk for heart attack and stroke, according to an observational study supported by the National Institutes of Health. The study, published in the Journal of the American Heart Association, uses data from nearly 435,000 American adults, and is among the largest ever to explore the relationship between cannabis and cardiovascular events.

The study, funded by the National Heart, Lung, and Blood Institute (NHLBI), part of NIH, found that daily use of cannabis — predominately through smoking — was associated with a 25% increased likelihood of heart attack and a 42% increased likelihood of stroke when compared to non-use of the drug. Less frequent use was also associated with an increased risk of cardiovascular events. Weekly users showed a 3% increased likelihood of heart attack and a 5% increased likelihood of stroke.

Around 75% of the study respondents reported that they mainly used cannabis by smoking the drug. Approximately 25% of the respondents reported using cannabis by some method other than smoking, such as vaping, drinking, or eating the drug.