Cannabis use found to raise heart attack risk among younger adults

Marijuana is now legal in many places, but is it safe? Two new studies add to mounting evidence that people who use cannabis are more likely to suffer a heart attack than people who do not use the drug, even among younger and otherwise healthy adults. The findings are from a retrospective study of over 4.6 million people published in JACC Advances and a meta-analysis of 12 previously published studies being presented at the American College of Cardiology's Annual Scientific Session (ACC.25).

Marijuana use has risen in the United States, especially in states where it is legal to buy, sell and use the drug recreationally. In the retrospective study, researchers found that cannabis users younger than age 50 were over six times as likely to suffer a heart attack compared to non-users. The meta-analysis, which is the largest pooled study to date examining heart attacks and cannabis use, showed a 50% increased risk among those who used the drug.

Asking about cannabis use should be part of clinicians' workup to understand patients' overall cardiovascular risk, similar to asking about smoking cigarettes. At a policy level, a fair warning should be made so that the people who are consuming cannabis know that there are risks."

 Ibrahim Kamel, MD, clinical instructor at the Boston University Chobanian & Avedisian School of Medicine and internal medicine resident at St. Elizabeth Medical Center in Boston and the study's lead author

Kamel and his team conducted the retrospective study using data from TriNetX, a global health research network that provides access to electronic medical records. Their findings indicate that over an average follow-up of over three years, cannabis users had more than a sixfold increased risk of heart attack, fourfold increased risk of ischemic stroke, twofold increased risk of heart failure and threefold increased risk of cardiovascular death, heart attack or stroke. All study participants were younger than age 50 and free of significant cardiovascular comorbidities at baseline, with blood pressure and low-density lipoprotein (LDL) cholesterol levels within a healthy range and no diabetes, tobacco use or prior coronary artery disease.

For the meta-analysis, the researchers pooled data from 12 previously published research studies that collectively included over 75 million people. The studies were rated as being of moderate to good quality in terms of methodology. Of the 12 studies, 10 were conducted in the United States, one in Canada and one in India. Some of the studies did not include information about participants' ages, but the average age was 41 years among those that did, suggesting that the pooled sample reflected a relatively young population.

Taken individually, seven of the studies found a significant positive association between cannabis use and heart attack incidence, while four showed no significant difference and one showed a slightly negative association. When the researchers pooled the data from all studies and analyzed it together, they found a significant positive association, with active cannabis users being 1.5 times as likely to suffer a heart attack compared with those who aren't current users.

Cannabis use and heart attack incidence was assessed in a similar manner across the different studies. However, due to inconsistencies in the data available from each study, researchers were unable to account for several potential confounding factors including the duration and amount of cannabis use or the use of tobacco or 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 number one advocate and having the full story matters."

While the mechanisms through which marijuana or its components may impact the cardiovascular system are not fully understood, the researchers hypothesize that it can affect heart rhythm regulation, heighten oxygen demand in the heart muscle and contribute to endothelial dysfunction, which makes it harder for the blood vessels to relax and expand, and can interrupt blood flow. One of the studies included in the meta-analysis found that the risk of heart attack peaked about one hour after marijuana consumption.

Since both studies were limited by their retrospective nature and the meta-analysis was limited by the challenges inherent in pooling data from multiple studies, researchers said that additional prospective studies would help to confirm the findings and determine which groups may face the highest risk. 

A previous study presented at the American College of Cardiology's Annual Scientific Session in 2023 found that daily marijuana use was associated with an increased risk of developing coronary artery disease. 

The meta-analysis will simultaneously publish in JACC Advances.