Cardiovascular Impact of Marijuana Use Remains Cloudy

A scan of the literature shows that there is a dearth of evidence regarding the potential cardiovascular effects—either good or bad—of marijuana use, a potentially concerning gap in knowledge at a time when the drug is becoming more widely available due to expanding legalization.

“Our review found insufficient data to draw meaningful conclusions on the associations between marijuana use and cardiovascular health outcomes,” lead author Divya Ravi, MD (Wright Center for Graduate Medical Education, Scranton, PA), told TCTMD in an email. “With decreasing risk perception, increasing legalization, and a rising number of users, there is a need for better understanding of the health effects of chronic marijuana use on adult populations, especially middle-aged populations with other comorbidities.”

Prior research has provided evidence that marijuana “can bring about changes at the tissue level and has the ability to potentiate vascular disease, in ways similar to tobacco,” Ravi explained, but the potential cardiovascular impact has not been well established.

Diabetes, Obesity, Acute MI, Mortality?

Ravi and her colleagues summarize the available data in a review published online January 22, 2018, ahead of print in Annals of Internal Medicine. They searched the literature for observational and interventional studies involving adults who used any form of marijuana, finding 13 studies with information on cardiovascular risk factors and 11 with outcomes data.

Six of those studies, all cross-sectional in design, indicated that using cannabis could have positive metabolic effects, including reductions in the prevalence of diabetes and glucose levels and an increase in HDL cholesterol. Those findings were not confirmed in prospective studies, however. In fact, one study showed that people who used marijuana at least 100 times during follow-up had an elevated prediabetes risk.

Several studies explored the association between cannabis use and obesity, with most showing no relationship with body mass index (BMI). Three other studies suggested a link between marijuana use and lower BMI, but the authors say they were limited by various factors. “Despite the popular belief that marijuana use causes ‘the munchies’, we found no evidence that it is associated with weight gain or obesity,” they say.

Looking at clinical outcomes, Ravi et al note that although there is one study suggesting that marijuana use may increase the risk of acute MI and a few studies suggesting that it may raise risks of all-cause and cardiovascular mortality, there is insufficient evidence to draw any definitive conclusions.

Existing studies are subject to several limitations, they say, including recall bias, predominantly cross-sectional designs, inadequate assessment of marijuana exposure, the inclusion of people with minimal exposure or low overall risks, and subpar statistical adjustment.

“Many articles in the lay press have suggested to the public that marijuana use has cardiovascular benefits, reduces blood pressure, stabilizes blood sugar levels, or improves cholesterol profiles,” the authors point out. “Our review found insufficient evidence to support these claims. Given public opinion that marijuana is safe or even beneficial, the insufficiency of the literature is concerning. An active research agenda in this area is needed to provide the public with accurate information.”

What are needed are robust longitudinal studies with adequate assessment of marijuana exposure, particularly in older adults, Ravi said. Determining exposure can be challenging, she added, because of the different ways marijuana is consumed.

Despite the challenges, though, further research is important. “In light of rising concentrations of THC in marijuana, a better understanding of the potential adverse effects is needed,” Ravi said.