Marijuana Could Increase Heart Attack Risk, Reduce Chances Of Kidney Failures, Studies Show

The use of marijuana could increase the risk of heart attacks, but it could decrease the likelihood of sudden kidney failures, two new studies have found.

The studies, which were presented at the American Heart Associations' Scientific Sessions on Nov. 9, showed the use of marijuana could increase the risk of stroke and bleeding in people after heart surgeries, including percutaneous coronary intervention or PCI. It also showed marijuana users were more prone to a second heart attack after heart surgeries than non-cannabis users.

To conduct the studies, researchers assessed more than 113,000 patients in Michigan who underwent an angioplasty procedure between January 2013 and October 2016. Of this, nearly 4,000 or 3.5% of patients said they used marijuana following the heart procedures. Interestingly, among patients who smoked cannabis following their PCI procedures, the chances of acute kidney failure were less compared to non-smokers.

"As marijuana use continues to increase, medical professionals and patients should be aware of these increased risks of complications after PCI," Sang Gune Yoo, an internal medicine resident physician at the University of Michigan and lead author of the study, said in a press release.

"Physicians should screen and counsel patients about marijuana prior to their procedure due to the risks of serious complications," he added.

Devraj Sukul, an interventional cardiologist at the University of Michigan and a senior study author, said the studies have limitations and further research is required.

"Understanding whether the effects of marijuana are dose-dependent or related to the method of intake are two important limitations of this study and remain important questions for future research," he said in the release.

Some experts say the studies showed contradictory findings.

Dr. Deepak Cyril D'Souza, a professor of psychiatry at the Yale University School of Medicine, told NBC News that the studies should determine the manner through which risks increase among patients. The studies need to assess if the risk comes from marijuana, the THC in marijuana, or from the mere burning of a plant-based product, he said.

Dr. Peter Grinspoon, a cannabis expert and an instructor at Harvard Medical School, said the studies contain contradictory findings.

"On the one hand, researchers are reporting increases in stroke, bleeding and second heart attacks in those using cannabis, but on the other, they are reporting improvements in cardiovascular risk factors, such as hypertension, high cholesterol and diabetes," Grinspoon, who is also a board member of Doctors for Cannabis Regulation, told NBC News.