Unexpected findings add new insight on cannabis and heart health

by University of California, San Francisco

edited by Sadie Harley, reviewed by Robert Egan

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Habitual cannabis users experienced about 9% fewer premature heartbeats on days they inhaled cannabis compared with days they abstained, a counterintuitive finding that adds to the complex and evolving understanding of how cannabis affects the heart, according to new UC San Francisco-led research.

The study, published in the Journal of the American College of Cardiology, is among the first to examine the acute cardiovascular effects of inhaled cannabis in people living their normal daily lives. While the findings challenge assumptions drawn largely from observational studies, the researchers caution that they should not influence medical or behavioral decisions around cannabis use.

With millions of Americans using cannabis, studies like this are increasingly important for understanding its health effects, the researchers said.

"We were surprised by the results because they contradicted our original hypothesis," said Gregory Marcus, MD, MAS, an endowed professor of atrial fibrillation research in the UCSF Division of Cardiology. "That's why randomized trials are so important. When the data challenge our expectations, our job as scientists is to understand them, not ignore them."

The trial enrolled 108 adults who regularly smoked or vaped cannabis but had no history of clinically diagnosed cardiac arrhythmias. Over 14 days, participants were randomly assigned each day to either inhale cannabis or abstain while wearing a continuously recording electrocardiographic monitor, activity tracker, sleep monitor and continuous glucose monitor.

Participants served as their own controls, allowing investigators to compare physiological changes during cannabis use and abstinence days.

Strongest predictor of premature atrial contractions

Unlike previous studies that relied largely on participants' self-reports or medical records, this randomized crossover trial continuously monitored every heartbeat, enabling researchers to measure physiological changes in real time under everyday conditions.

Researchers found that cannabis inhalation was associated with a statistically significant reduction in extra or early heartbeats, known as cardiac ectopy. The reduction was driven by fewer extra heartbeats that began in the heart's upper chambers, known as premature atrial contractions (PACs).

The frequency of PACs is the single most potent predictor of atrial fibrillation, while PVCs can predict heart failure. Although these early heartbeats are common, researchers still know relatively little about what determines their frequency.

No significant change was observed in extra heartbeats originating in the lower chambers, called premature ventricular contractions (PVCs).

A clue, not a health endorsement

The researchers found no significant differences in daily step counts, sleep duration or glucose levels, which was also surprising. Together, the findings illustrate how randomized trials can produce a different and more nuanced picture than observational research alone.

Marcus emphasized that the findings should not be interpreted as evidence that cannabis benefits cardiovascular health.

"This study examined the acute effects of cannabis in people who use it regularly and was not designed to evaluate the long-term health consequences," he said.

"The overall health effects of inhaled cannabis may still be net negative, but these findings suggest there may be something about cannabis that can teach us more about the biological mechanisms that produce premature atrial contractions. That knowledge could eventually lead to new approaches for preventing or treating abnormal heart rhythms."

Publication details

Acute Effects of Cannabis Inhalation on Cardiac Ectopy, Physical Activity, Sleep, and Glucose, Journal of the American College of Cardiology (2026). DOI: 10.1016/j.jacc.2026.07.014

Journal information: Journal of the American College of Cardiology

Key medical concepts

Premature ventricular contractionsArrhythmia

Clinical categories

Cardiology Provided by University of California, San Francisco Who's behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →

Robert Egan

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