News release

From: American College of Cardiology

Unexpected Findings Add New Insight on Cannabis and Heart Health

UCSF trial found fewer premature heartbeats after cannabis inhalation, with potential implications for atrial fibrillation risk.

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, new UC San Francisco-led research found.

The study, published August 12 in the Journal of the American College of Cardiology, is among the first randomized crossover trials 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 these findings should not influence medical or behavioral decisions around cannabis use.

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

"We were surprised by the results because they contradicted our original hypothesis," said Gregory Marcus, MD, MAS, an endowed professor in 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 control, allowing investigators to compare physiological changes during cannabis-use and abstinence days.

Capturing heart rhythm in everyday life

Unlike previous studies that relied largely on participants' self-reports or medical records, the 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), while no significant change was observed in extra heartbeats originating in the lower chambers, called premature ventricular contractions (PVCs).

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.

The researchers also found no significant differences in daily step counts, sleep duration, or glucose levels, 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."