In recent years, weed use among U.S. adults has reached an all-time high. While many laud this drug as safe, natural, and even medicinal, a growing body of evidence suggests it contributes to adverse cardiovascular effects—including deadly heart disease. 

A new study published in the journal Heart on Tuesday, June 17, presents new evidence showing that marijuana use doubles the risk of dying from cardiovascular disease. The researchers found particularly heightened risks of stroke and acute coronary syndrome (ACS)—a sudden reduction in blood flow to the heart, such as a heart attack. While previous studies have linked cannabis to cardiovascular problems, this research underscores the severity of these risks. The authors note, however, that future studies will need to verify this link and investigate the mechanisms behind it. 

The findings may come as a shock to those who consider weed a harmless high, but co-author Emilie Jouanjus, a clinical pharmacologist at the University of Toulouse in France, was not surprised. She’s been studying the adverse health effects of marijuana for more than a decade and hopes this study will promote better decision-making around marijuana use. 

“I think that it’s very important that people realize that there is risk, even if it’s a natural product,” Jouanjus told Gizmodo. Over the last decade, increased state legalization has made weed more accessible and less stigmatized, contributing to a rise in recreational and medicinal use. Jouanjus and her colleagues argue that public health messaging should treat cannabis like tobacco—not criminalizing it, but actively highlighting its risks and discouraging use.

The researchers analyzed 24 studies, conducted between January 2016 and December 2023, that investigated the link between marijuana use and serious cardiovascular outcomes. These studies involved roughly 200 million participants mostly between the ages of 19 and 59. They specifically looked at cardiovascular disease death and non-fatal outcomes including stroke and ACS.

The analysis found that cannabis use increases the risk of ACS by 29%, risk of stroke by 20%, and doubles the risk of dying from cardiovascular disease. While the researchers say their study provides an exhaustive analysis of the available data on marijuana use and cardiovascular disease, Jouanjus noted that the included studies were limited by a lack of data on when and how participants were exposed to cannabis.

This leaves several important questions unanswered, such as, at what dosage does cannabis become unsafe? Are the cardiovascular risks lower for occasional marijuana users? Is consuming edibles safer than smoking weed? Jouanjus hopes future studies will explore these questions. Some researchers have already begun, like Matt Springer, a cardiovascular researcher at the University of California San Francisco. 

Springer co-authored a recent study, published in the journal JAMA Cardiology in May, that found both smoking weed and eating edibles increase risk of cardiovascular disease. The finding challenges widespread assumptions that edibles are a less-harmful way to consume marijuana and underscores the drug’s alarming cardiovascular effects. 

Like Jouanjus, Springer wasn’t surprised by the link between cannabis use and cardiovascular disease death. “This is consistent with several reports in the last few years showing associations between cannabis use and various kinds of cardiovascular outcomes, as well as another recent meta-analysis reported at the [American College of Cardiology] conference in March,” he told Gizmodo in an email. That study found that cannabis users face significantly higher risk of heart attack than non-users. 

Springer’s latest study found that cannabis users showed reduced blood vessel dilation, which puts them at greater risk of heart attack and other poor cardiovascular outcomes. In theory, this could contribute to the increased risk of cardiovascular disease death that Jouanjus and her colleagues found, he said, but researchers need more evidence to support that claim.

There are other potential mechanisms, too. Jouanjus pointed to previous research that found that, like tobacco, cannabis contributes to buildup of plaque within artery walls. This increases the risk of heart attack, stroke, and peripheral artery disease. She also highlighted that the psychoactive compound in marijuana—tetrahydrocannabinol (THC)—is far more concentrated in cannabis products today than those from 20 years ago. This, too, may contribute to the increased risk of cardiovascular death she observed in her study.

While all of these factors could plausibly influence weed’s cardiovascular effects, getting to the bottom of why this drug damages heart health will require more research. In the meantime, Jouanjus feels there is enough evidence to warrant caution and moderation when using marijuana. The public is well aware of the benefits of cannabis, but she hopes her study can draw attention to its risks, too.

Springer agrees, “These reports over the last few years, including ours and this paper, indicate that cannabis is not necessarily harmless,” he said.