As more and more states continue to legalize marijuana, researchers from the Einstein Medical Center in Philadelphia may have found a reason to exercise caution. In a large study that analyzed inpatient hospital records, they determined that cannabis use was associated with a significantly higher risk of heart failure and stroke, even after accounting for lifestyle factors.
The research will be presented by lead author Aditi Kalla, MD, this week at the American College of Cardiology’s 66th Annual Scientific Session in Washington, DC. According to Kalla, who spoke with reporters in a preconference briefing, the impetus for the study was the boom in marijuana use for both medical and nonmedical purposes, despite the scarcity of research on its potential harms.
“Like all other drugs, whether they’re prescribed or not prescribed, we want to know the effects and side effects of this drug,” said Kalla in a press release. “It’s important for physicians to know these effects so we can better educate patients, such as those who are inquiring about the safety of cannabis or even asking for a prescription for cannabis.”
Researchers pored over the health records of 20 million patients aged 18 to 55 years that were gathered in the Nationwide Inpatient Sample in 2009 and 2010 and found that about 316,000, or 1.5%, indicated the patient had been diagnosed with marijuana use. These patients, the researchers determined, were more likely to be male than the non-users and had higher rates of tobacco and alcohol use.
The study authors detected some concerning patterns among the group of marijuana users. They were significantly more likely to experience sudden cardiac death, heart failure, coronary artery disease, or a cerebrovascular accident like a stroke. Since cannabis use was also linked to several known cardiovascular risk factors, however, the researchers performed further analyses to account for these factors.
After controlling for a plethora of factors including age, sex, hypertension, diabetes, tobacco use, and alcohol use, the marijuana users were still significantly more likely to experience heart failure or a cerebrovascular accident. According to Kalla, this indicates that cannabis itself is an independent predictor of cardiovascular events, though the exact mechanisms remain unclear.
“Even when we corrected for known risk factors, we still found a higher rate of both stroke and heart failure in these patients, so that leads us to believe that there is something else going on besides just obesity or diet-related cardiovascular side effects,” she said in the press release. “More research will be needed to understand the pathophysiology behind this effect.”
Previous research could hold some clues about the biological pathways putting marijuana users at risk for cardiac problems. Last fall, a study revealed that young men who used marijuana were twice as likely to experience stress cardiomyopathy, a weakening of the heart muscles that impedes the heart’s ability to pump. Research using cell cultures found that the muscle cells of the heart have cannabinoid-1 receptors, which, when activated, make it harder for the muscle cells to contract.
Kalla and her co-authors acknowledged some limitations of their research, like the risk of underreporting, as the drug was illegal in most states during the study period. They also suggested that future studies should examine whether cardiovascular risk is affected by the quantity or method of cannabis use. Still, they indicated, this study’s large sample size and rigorous controlling for factors like tobacco use make it a valuable contribution to the growing field of research on the health effects of marijuana.
Marijuana use is fully legal in 8 states plus the District of Columbia, where the conference will take place. An analysis after voters in several states approved marijuana use in 2016 found that 1 in 5 Americans live in states where marijuana use is legal, yet this drug has not been evaluated by the FDA for safety or effectiveness.