A recent study has suggested that 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.
The study, by the University of California-San Francisco-led research team and 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 these findings should not influence medical or behavioural decisions around cannabis use.
With millions of Americans using cannabis, studies like this are increasingly important to understand 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, UCSF Division of Cardiology
“That’s why randomised 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.
Greatest predictor of premature atrial contractions
Unlike previous studies that relied largely on participants’ self-reports or medical records, this randomised crossover trial, the gold standard for trials, 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, or 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 (PVC).
The researchers found no significant differences in daily step counts, sleep duration, or glucose levels, also surprising. Together, the findings illustrate how randomised trials can produce a different and more nuanced picture than observational research alone.
Marcus emphasised 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.”
Study details
Acute Effects of Cannabis Inhalation on Cardiac Ectopy, Physical Activity, Sleep, and Glucose
Adi Elias, Gabrielle Montenegro, Hannah Oo et al.
Published in JACC on 12 August 2026
Abstract
Background
Inhaled cannabis is widely legal in the US. Data regarding cardiovascular effects are conflicting and generally arise from observational studies.
Objectives
The goal was to evaluate the acute effects of cannabis inhalation on cardiac ectopy.
Methods
We conducted a prospective, randomised, crossover trial to assess effects of inhaled cannabis on cardiac ectopy, mean glucose levels, step counts, and sleep durations. Adults who smoked or vaped cannabis on a regular basis without a history of cardiac arrhythmias were enrolled. Participants were randomly assigned each day to inhale vs abstain from cannabis via text messages for 14 days. Adherence was assessed using time-stamped Zio patch button presses at the time of cannabis use, daily surveys, and, in a subset, salivary mass spectrometry. The primary outcome was daily cardiac ectopy (daily premature atrial contractions and premature ventricular contractions).
Results
Of 108 participants (mean age 32 ± 10 years, 59% women, and 37% non-Hispanic white) experiencing a total of 713 days randomised to inhaled cannabis and 616 days randomised to abstinence, randomisation adherence was imperfect but generally supportive of assignment adherence. Inhaled cannabis resulted in a statistically significant 9% reduction in ectopic beats (rate ratio [RR]: 0.91; 95% CI: 0.85-0.98; P = 0.02). Daily premature atrial contractions decreased by 10% (RR: 0.90; 95% CI: 0.82-0.97; P = 0.012), whereas premature ventricular contractions showed no significant change. Each cannabis inhalation was associated with a 2% reduction in ectopic beats (RR: 0.98; 95% CI: 0.97-0.99; P = 0.043). No significant differences were observed for step counts, sleep duration, or glucose levels.
Conclusions
In a pragmatic crossover design including habitual cannabis users, randomisation to inhaled cannabis was associated with less cardiac ectopy, driven by fewer premature atrial contractions. Potential withdrawal effects, moderate adherence, and co-intervention limit interpretation of causal mechanism. (Marijuana and Acute Risk of Arrhythmia-Joint Abstinence and Exposure [MARY-JANE]; NCT06021613)
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