Aside from a bit of nausea or a touch of anxiety now and then, cannabis is the perfect drug, right? Studies are showing all sorts of upside, and little downside: There’s never been an overdose, the risks of addiction are tiny compared to prescription meds, and the side effects are few, rare, and minor.
All true … but not so fast.
Public perception is rightly shifting in favor of greater acceptance, but we still know very little about the long-term effects of regular consumption. After decades of federal prohibition against cannabis research, scientists are only beginning to explore the totality of its impacts on the human body.
Case in point: Doctors sounded a cautionary note this winter with the release of a report that should give pause to any frequent pot smoker. Presented at an American Heart Association conference in November, and later published in the journal Stroke, the study examined data from more than 43,000 people aged 18–44. One out of seven participants had reported using cannabis in the past month, forming a large cohort whose histories the authors analyzed for cardiovascular events and risk factors.
Related: 14 Ways Cannabis Does a Brain Good
Their findings were striking. After normalizing the data for other risk factors, the study suggested that people who were using marijuana more than 10 days a month were almost 2.5 times more likely to suffer a stroke than non-users. And it was worse for those who also smoked cigarettes or e-cigarettes, as well; their risk grew to three times.
The researchers were quick to point out that the study was purely observational, and not the kind of long-term clinical trial needed to establish a causal link. Federal funding is one challenge, but finding enough pot-smoking stroke victims may be a bigger complication—in the universe of health threats, stroke, fortunately, remains very uncommon. That said, lead author Tarang Parekh, M.B.B.S., M.S., a health policy researcher at George Mason University, did issue this warning: “Young cannabis users, especially those who use tobacco and have other risk factors for strokes, such as high blood pressure, should understand that they may be raising their risk of having a stroke at a young age.” He also suggested that physicians should be asking patients about their cannabis use and counseling them about potential stroke risk.
The study suggested that people who were using marijuana more than 10 days a month were almost 2.5 times more likely to suffer a stroke than non-users.
This study is not the first to point to a possible link between heavy marijuana use and stroke. A 2018 analysis of U.S. hospital data from 2010–2014 estimated that stroke risk increases with chronic use, but by a smaller amount—15% to 29%—than the AHA report. Separately, a small New Zealand study of 218 stroke sufferers found that marijuana users were roughly twice as likely to experience ischemic attacks. It also suggested that your risk is greatest in the first 60 minutes after finishing a joint.
What’s not clear yet is true causation. Because most of the data has come from pot smokers, rather than a diverse set of cannabis users, scientists can’t divine the impact of the plant versus the smoke. Are cannabinoids to blame? We know they elevate heart rate, dilate blood vessels, and make the heart pump harder. And people with heart disease develop chest pain more quickly in stress tests if they smoked pot first. Or is the act of smoking to blame? Cigarettes elevate stroke risk and the likelihood of heart disease, so it’s plausible that chronic bong-hitters are more susceptible to attacks than people using topicals and edibles. The conundrum points out the need for rigorous, focused research.
For now, no one is suggesting abstinence for the average cannabis fan. The Harvard Health Letter, for instance, said last fall that smoking marijuana “does not pose a significant threat to people who have minimal cardiovascular risk.” That said, heavy tokers with a previous history of strokes or heart disease should consider cutting back or quitting. And following Parekh’s logic, young people with risk factors may want to moderate their smoking—or try gummies. After all, strokes are rare, but you only have one brain.