SAN FRANCISCO — The study included 108 adults who regularly smoked or vaped cannabis and had no history of clinically diagnosed cardiac arrhythmias. At baseline, the average age of participants was 32 years, and 59% of study participants were women. None of the participants had diabetes, while 8% of participants had hypertension.

Participants were randomly assigned each day to inhale cannabis products or abstain completely via text messages for 14 days. There were a total of 713 days randomized to inhaled cannabis and 616 days randomized to abstinence. During follow-up, participants were equipped with a continuously recording ECG patch, a wrist-worn Fitbit activity tracker and sleep monitor, and a continuous glucose monitor for the first 10 days.

Inhaled cannabis in the study included smoked cannabis (joints, blunts, pipes, and bongs) and vaped cannabis. The most commonly reported methods of cannabis inhalation were joints (63%) and vape cartridges (57%). Frequency of cannabis use ranged from one to four times per month to three times or more per day. Fewer than one in three participants smoked tobacco or vaped nicotine concurrently.

The median number of extra or early heartbeats was 13 per day on cannabis days versus 13.8 per day off cannabis. The rate ratio for extra or early heartbeats was 0.91 (95% CI 0.85-0.98). Each cannabis inhalation was associated with a 2% reduction in ectopic beats, with a rate ratio for ectopic beats per inhalation of 0.98 (95% CI 0.97-0.99).

The change in daily ectopy was driven by a decrease in daily premature atrial contractions (PACs). The median number of premature atrial contractions was 7 on cannabis days versus 9.75 on off-cannabis days. The rate ratio for premature atrial contractions was 0.90 (95% CI 0.82-0.97). Premature ventricular contractions (PVCs) were unchanged on days using cannabis, with a median of 3 on cannabis days versus 2.75 on off-cannabis days and a rate ratio of 1.01 (95% CI 0.91-1.12).

No significant differences were observed for step counts, sleep duration, or glucose levels. Adherence to instructions to inhale or avoid cannabis was deemed moderate based on time-stamped Zio patch button presses, daily surveys, and salivary mass spectrometry. Participants were not blinded to their exposure and were instructed to use their own cannabis products.

The selection criteria excluded anyone who had a history of atrial fibrillation or heart failure, an implanted pacemaker or implantable cardioverter-defibrillator, or who had been prescribed beta-blockers, nondihydropyridine calcium-channel blockers, or Vaughn-Williams class 1 or 3 antiarrhythmic medications. The selection criteria also excluded anyone who had a medical reason to avoid cannabis. The trial did not assess other effects of acute cannabis inhalation and did not collect data on alcohol consumption.

Why It Matters

The study identifies a specific physiological effect of inhaled cannabis on cardiac rhythm, distinguishing between different types of ectopic beats. By demonstrating a reduction in premature atrial contractions without a corresponding change in premature ventricular contractions, the research isolates a potential mechanism within the atria. This distinction is relevant because premature atrial contractions are a known predictor of atrial fibrillation, a condition that affects millions of people and increases stroke risk. The findings suggest that lifestyle factors may influence these precursor events, although the net health impact of cannabis remains complex.

The trial design, which allowed participants to use their own products, reflects real-world usage patterns but limits the ability to pinpoint specific chemical constituents responsible for the observed effects. Understanding how common exposures affect cardiac electrophysiology could inform both patient counseling and future therapeutic strategies for arrhythmia prevention, even if the substance itself carries other health risks.

Timeline

Aug. 12: Study published in the Journal of the American College of Cardiology.

What's New

The official record of the event states that inhaled cannabis was associated with a statistically significant reduction in premature atrial contractions (PACs) among habitual cannabis users, with a 9% decrease in premature heartbeats. Gregory Marcus said, "We were surprised by the results because they contradicted our original hypothesis." He added, "When the data challenge our expectations, our job as scientists is to understand them, not ignore them." Marcus also stated, "That's why randomized trials are so important." The study was published Aug. 12 in the Journal of the American College of Cardiology. Research titled A randomized crossover trial of the effects of fermented milk on carotenoid absorption in healthy participants was published in 2025 in F1000Research. Research titled Relative Bioavailability of Zongertinib, an Orally Administered HER2-Selective Tyrosine Kinase Inhibitor, under Fed and Fasted Conditions in Healthy Male Participants: Results from was also noted. The trial enrolled 108 participants, but the clinical trial registry (NCT06021613) initially listed the expected number as 100, indicating a discrepancy in participant numbers.

How Sources Differ

Regarding premature atrial contractions, the desk_web source states that the official record indicates a reduction among habitual users with a 9% decrease in premature heartbeats, while the Journal of the American College of Cardiology study reports a rate ratio for premature atrial contractions of 0.90 (95% CI 0.82-0.97). On the topic of cannabis associated reduction, the desk_web source cites the 9% decrease in premature heartbeats, whereas the Journal of the American College of Cardiology study notes that each cannabis inhalation was associated with a 2% reduction in ectopic beats. Concerning the reduction in premature heartbeats from inhaled cannabis, the Journal of the American College of Cardiology study explicitly states there was a 9% reduction on days participants inhaled cannabis compared with days they abstained, while the desk_web source frames this as part of the official record stating an association with reduced PACs.

Regarding inhaled cannabis and premature atrial contractions, the desk_web source presents the official record of the association, while Marcus stated that the overall health effects may still be net negative but the findings offer insight into biological mechanisms. On the subject of cannabis and premature atrial contractions, the desk_web source cites the official record, while the Journal of the American College of Cardiology study provides specific median numbers of 7 on cannabis days versus 9.75 on off-cannabis days. For inhaled cannabis in habitual users, the desk_web source references the official record, while the Journal of the American College of Cardiology study describes the trial as examining acute cardiovascular effects in this population. Regarding the decrease in premature atrial contractions, the desk_web source includes this in its summary of the official record, while the Journal of the American College of Cardiology study specifies that the change in daily ectopy was driven by this decrease.