While marijuana is becoming more available nationwide as medicine and for recreational use, two new studies build on growing evidence that cannabis users are more apt to have heart attacks than those who do not use the drug. And it’s true even among young, healthy adults.

Cannabis users who are not yet 50 are six times as likely to have heart attacks as those who don’t use the drug, per a retrospective study involving 4.6 million people that was published in JACC Advances, one of the American College of Cardiology’s journals. And a review of 12 previous studies — the largest to look at the issue of heart attacks and cannabis use — found 50% increased risk among cannabis users.

The findings are being presented at the American College of Cardiology’s Annual Scientific Session next week in Chicago.

UPI.com reported that marijuana is legal for recreational use in 24 states and for medical use in 39 states.

“Asking about cannabis use should be part of clinicians’ workup to understand patients’ overall cardiovascular risk, similar to asking about smoking cigarettes,” said Dr. Ibrahim Kamel, clinical instructor at the Boston University Chobanian & Avedisian School of Medicine and internal medicine resident at St. Elizabeth Medical Center in Boston, who led the study. “At a policy level, a fair warning should be made so that the people who are consuming cannabis know that there are risks.”

Studies highlight risks

The retrospective study took data from TriNetX, a global health research network that lets researchers use electronic medical records. Over follow-up averaging more than three years, the researchers found that cannabis users had:

• More than a sixfold increased risk of heart attack
• Fourfold increased risk of ischemic stroke
• Twofold increased risk of heart failure
• Threefold increased risk of cardiovascular death, heart attack or stroke

Those participants were all younger than 50 and didn’t have any significant cardiovascular problems when the study began, “with blood pressure and low-density lipoprotein (LDL) cholesterol levels within a healthy range and no diabetes, tobacco use or prior coronary artery disease,” according to a news release on the study.

In the other study, which reviewed an international collection of previous research involving more than 75 million people, mostly conducted in the U.S., seven found a link between cannabis use and having a heart attack, four didn’t, and one suggested less risk. When all the study data was pooled, a link between cannabis use and heart attack was significant. Users were 1.5 times as apt to have a heart attack compared to those not currently using.

Not all of those studies included age, but among those that did, 41 years old was average, suggesting “a relatively young population,” the researchers said.

Dr. Sameer Amin, cardiologist and chief medical officer at L.A. Care Health Plan, who was not part of the research, told Healthline that more research is needed. But “based on early information showing an association of cannabis with an increased risk of worse cardiovascular outcomes, there appears to be an emerging concern.”

Why cannabis might increase risk of heart attack isn’t known, the researchers theorize it could impact heart rhythm, increase oxygen demand in the heart and make it harder for blood vessels to relax and expand, thus changing blood flow. The release noted that one study found the risk of heart attack peaked an hour after marijuana consumption.

Study limitations

Because of the data, the researchers couldn’t eliminate the possibility of confounders that could also influence the results, such as the amount and duration of cannabis use or use of tobacco and other drugs.

“We should have some caution in interpreting the findings in that cannabis consumption is usually associated with other substances such as cocaine or other illicit drugs that are not accounted for,” Kamel said. “Patients should be forthcoming with their doctors and remember that we are their No. 1 advocate and having the full story matters.”

The researchers said they’re hoping to do more studies on the issue. They note an earlier study presented at the American College of Cardiology’s Annual Scientific Session in 2023 found daily marijuana use increased risk of developing coronary artery disease.