Scientists Tracked Cannabis Users' Hearts Day by Day—One Finding Stood Out

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Millions of Americans use cannabis, which is now legal in multiple states. According to a report from the Centers for Disease Control, around 52.5 million people used it at least once in 2021.

Now, a new study published in the Journal of the American College of Cardiology has suggested that those who use cannabis experience fewer extra or early heartbeats on days they smoke or inhale compared to days they do not.

The study, based on 108 adults who regularly smoked or vaped cannabis but had no history of clinically diagnosed cardiac arrhythmias, took place over 14 days.

Each participant wore a continuously recording electrocardiographic monitor, glucose monitor, activity tracker and sleep monitor, and, on each day, was randomly assigned to either inhale cannabis or to abstain.

It found that regular cannabis users on the trial experienced about 9 percent fewer premature heartbeats on days they inhaled cannabis compared with days they abstained from it.

Senior author of the paper Gregory Marcus, MD, MAS, told Newsweek that healthy people who regularly used cannabis experienced "significantly less abnormal, early heart beats" when they smoked or vaped cannabis in the trial, compared to days they were told to avoid all cannabis.

"Those early heartbeats are common in the general population, and we now recognize that more of them can lead to important forms of heart disease ."

Studies show that experiencing early and extra heartbeats is common, but little is yet known about what determines their frequency.

In this study, the significant reduction in extra or early heartbeats—also known as cardiac ectopy—was driven by fewer heartbeats beginning in the heart's upper chambers, also known as premature atrial contractions (PACs).

No significant change was observed in extra heartbeats from the lower chambers (PVCs).

PAC frequency is a predictor of atrial fibrillation—a heart rhythm disorder where the upper chambers beat irregularly and which can lead to serious issues such as blood clots or stroke. The frequency of PVCs, meanwhile, can predict future heart failure.

Marcus acknowledged that "heart rate patterns during the study differed in ways expected." However, he added that the continuously recording sensors found "no differences in sleep times, step counts, or blood glucose levels."

He warned in a news release that the study's findings should not be interpreted as evidence that cannabis is good for a person's cardiovascular health, and that the overall health effects of inhaled cannabis may still be net negative.

A 2024 study published in the Journal of the American Heart Association , based on 430,000 United States adults, found that frequent cannabis use may increase the risk of heart attack and strokes.

However, this study suggests that the effect of cannabis may be able to teach researchers more about the biological mechanisms that produce premature atrial contractions.

The new UCSF study is among the first randomized crossover trials to examine the acute cardiovascular effects of inhaled cannabis in people living their everyday lives, and challenges assumptions drawn from previous, largely observational studies.

Researchers have cautioned that the findings of this study should not influence medical or behavioral decisions around cannabis use.

Marcus, a professor in atrial fibrillation research and associate chief of cardiology for research at UCSF, told Newsweek they hope the research will "motivate future randomized trials."

These trials, he said, "are the only way to fully avoid confounding effects that interfere with revealing underlying realities…that are so common in the majority of observational research."

He acknowledged that this study alone is "not sufficient" to change current recommendations or clinical practice, "but it may open up new areas of investigation into ways to suppress these common early beats and potentially to identify novel therapies that might be gleaned from constituents in cannabis."

Elias, A., Montenegro, G. C., et al. (2026). Acute effects of cannabis inhalation on cardiac ectopy, physical activity, sleep, and glucose. Journal of the American College of Cardiology . https://doi.org/10.1016/j.jacc.2026.07.014

Contact Newsweek editors on this story: Marc Vargas and James Debens

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