A full understanding of how marijuana affects the heart and blood vessels has yet to be reached, but some chemicals in cannabis — particularly THC, the psychoactive agent — have been linked to an increased risk of heart attacks, heart failure, and atrial fibrillation, according to the American Heart Association.

THC interacts with receptors that activate a person’s “fight-or-flight” response, explained Robert Page, a professor of clinical pharmacy at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences. As a result, your heart could start beating rapidly or irregularly, your blood vessels could constrict, or your blood pressure could skyrocket — all conditions that increase risk of heart attack and stroke.

Smoking pot has also been shown to increase blood concentrations of carbon monoxide, which is associated with chest pain, heart attacks, and abnormal heart rhythms.

And pot smokers experience a threefold increase in tar, which is inhaled through partly burnt plant matter.

On the other hand, cannabidiol (CBD), another marijuana chemical, appears to slow heart rate, lower blood pressure, relax the arteries, and potentially reduce inflammation — all things that are potentially good for heart health.

Until there is better data on risks versus benefits, “We definitely do not recommend that people use marijuana,” said Dr. Johanna Contreras, director of the division of heart failure at Mount Sinai St. Luke’s and Mount Sinai West, in New York City.