A recent study in BMJ Open, based on more than 50 million hospital records from 2012 to 2018, compared the Western U.S., where legal recreational marijuana sales began in 2014, with regions where legal sales had not yet begun. For each year of legal sales, hospitalizations for heart failure rose 3.7% faster in the West, heart attacks 3.1% faster, and atrial fibrillation, an irregular heart rhythm, 2.3% faster. The study, led by a Boston Medical Center cardiologist with co-authors from the Harvard T.H. Chan School of Public Health and Harvard Medical School, also found that hospitalizations for marijuana-related diagnoses rose 13.6% faster each year. The authors noted that “our findings point to potential adverse effects of [recreational] legalisation on population health.” While marijuana’s harms to mental health are increasingly recognized, studies like this one suggest it can harm physical health too.