Cannabis and Heart Rhythm: What a 2026 Randomized Crossover Trial Found

The MARY-JANE trial enrolled 108 adults who regularly smoked or vaped cannabis and had no history of cardiac arrhythmias. Over 14 days, participants were randomized by text message each day to inhale cannabis or abstain. Continuous Zio patch monitoring counted premature atrial contractions (PACs) and premature ventricular contractions (PVCs), while researchers also tracked sleep duration, steps and glucose.

Across 713 cannabis-assigned days and 616 abstinence-assigned days, inhaled cannabis was associated with a 9% reduction in total ectopic beats. The difference was driven by about 10% fewer PACs. PVCs did not change significantly, and the study found no significant differences in step counts, sleep duration or glucose levels.

The participants were habitual users, and adherence to the daily randomization was imperfect. The authors noted that withdrawal effects on abstinence days and other co-interventions could influence the result. The trial also measured one short-term physiological endpoint—not heart attacks, stroke, heart failure, atrial fibrillation or long-term cardiovascular mortality.

A substance can change one short-term marker without establishing its overall cardiovascular effect. Other research has linked cannabis exposure with changes in heart rate and blood pressure, and observational studies have reported associations with cardiovascular events. Those studies also have limitations, including confounding by tobacco, age, health status and patterns of use.

Randomized real-world exposure data are rare in cannabis research. An unexpected result should not be ignored simply because it conflicts with prior expectations. It should also not be overgeneralized. The appropriate response is to refine hypotheses and design studies that can separate withdrawal, dose, cannabinoid profile and route of administration.

Researchers need larger trials that characterize THC and CBD exposure, compare smoking with vaping and non-inhaled routes, include people who are not habitual users, track tobacco and alcohol carefully and follow clinically meaningful outcomes over longer periods.

The responsible headline is precise: this trial observed fewer premature atrial beats on inhalation days in habitual users. It did not show that cannabis prevents arrhythmias or protects the cardiovascular system. Counterintuitive findings are exactly where careful research communication matters most.