Legal marijuana is becoming more widely available across the United States, but a recent study printed in the Journal of the American College of Cardiology has cardiologists concerned about its health effects, particularly with whether cannabis is increasing the risk of premature myocardial infarction.

Medical cannabis has been approved in 30 states, while nine of those have approved it for recreational use. Meanwhile, it remains illegal at the federal level. The retrospective study reviewed medical records of patients who’d suffered a myocardial infarction under the age of 50 between 2000 and 2016. The patients’ substance use was tracked according to their own admission or by toxicology reports at the time of their MI. Researchers found that marijuana or cocaine were present in 10% of MI cases in patients under 50 and that marijuana and/or cocaine use was “associated with worse all-cause and cardiovascular mortality.”

According to the study authors, marijuana use has been linked to adverse cardiovascular events, including stroke, coronary artery dissection, vasospasm, coronary thrombosis, arrhythmias, and cardiomyopathies, among others. This may bode poorly for cannabis growers, who often tout the positive effects of marijuana in their legalization efforts. According to the DeFilippis study, the meta analysis revealed that the incidence of MI was “significantly higher” for patients with substance abuse when compared with patients without. Substance users also had a higher rate of cardiovascular mortality when compared with those who abstained.

Study authors DeFilippis et al further note that their findings support current recommendations of screening for substance abuse when patients less than 50 years old present with MI. Further, they state, “substance abuse is an important risk factor for developing premature MI and suggest that among patients who experience an MI, the use of cocaine or marijuana is associated with an adverse long-term prognosis.”

The study concludes that it’s reasonable for PCPs and cardiologists to caution recent heart attack patients at any age against marijuana use — that is, smoking marijuana, at least. An editorial that also ran in JACCpoints out some of the study’s limitations, one of which is that it focuses primarily on those who inhale marijuana smoke rather than ingesting it in edible forms — a rising trend now that legal cannabis is becoming increasingly available. Regardless, the JACC study suggests that more research on the effects of cannabis use on cardiovascular health are needed.