For Young Adults, Cannabis Tied to Doubling of MI Risk

Young adults who report regular, recent cannabis use are twice as likely to have experienced an MI in their lifetimes, US observational data suggest.

The absolute difference in MI between users and nonusers was 0.5%, Karim S. Ladha, MD (St. Michael’s Hospital, Toronto, Canada), and colleagues report in their paper, which was published Tuesday in CMAJ.

“Despite the widespread use of cannabis, its effects on health remain poorly understood,” they say, adding that their study is unique in its look at the frequency, recency, and modes of consumption.

An American Heart Association scientific statement released in 2020 specifies that, when it comes to cardiovascular health, marijuana appears to carry substantial risks and offer no benefits. One study has linked it to periprocedural MI after elective surgery, and just last month another tied use to poorer PCI outcomes.

Ron Blankstein, MD (Brigham and Women’s Hospital, Boston, MA), whose own work has shown an increased death risk in young MI patients who use marijuana or cocaine, told TCTMD the latest study draws awareness to the fact that marijuana—much like cigarettes or cocaine—is associated with higher risk of cardiovascular events. “Especially now as marijuana is legalized in many parts of the country, there is the perception by many that it is a benign substance, that there’s no harm,” said Blankstein, adding that the current study speaks to the contrary.

Still, the design is observational and thus the study may suffer from confounding, he said. A strength of its data is that the observed associations were greater among people reporting more-frequent marijuana use. Another is the focus on young adults, who are more apt to be cannabis consumers—here, nearly one in five people. “Probably most physicians are going to underestimate that figure,” Blankstein commented.

Frequent Users Most at Risk

The researchers gathered data from the American Behavioral Risk Factor Surveillance System for 2017 and 2018. Out of 33,173 young adults ages 18 to 44—representing 18.5 million people in the US population—around 18% reported using marijuana, cannabis, or hashish at least once within the past 30 days. Most (71%) said they used it more than four times during that period, with smoking as the predominant route (76%) followed by vaporization (11%) and other forms like edibles (12%). Use was more common among men, unmarried people, users of conventional or e-cigarettes, and heavy alcohol consumers. Around 22% of users were ages 18 to 24, while 37% were 25 to 34, and 41% were 35 to 44.

Adjusted for demographic and socioeconomic factors, health-related behavior, insurance status, other substance use, and comorbidities, people who used cannabis were more likely to have a history of MI than nonusers (1.3% vs 0.8%; OR 2.07; 95% CI 1.12-3.82). This association was similar for people who used cannabis more than four times per month (OR 2.31; 95% CI 1.18-4.50) but attenuated for those who did so less frequently (OR 1.48; 95% CI 0.52-4.21).

I think we have to pay attention to this signal. Ron Blankstein

MI risk was higher for people whose method of marijuana use was mainly smoking (OR 2.01; 95% CI 1.02-3.98); for other modes of ingestion, risks were similarly elevated but not significantly so. Risk of MI was also elevated for current tobacco smokers (OR 2.56) and smokeless tobacco users (OR 1.88) as compared with nonusers, both statistically significant differences.

What to Tell Patients?

For clinicians counseling patients, the message is clear, Blankstein said: “This study is not in isolation. There are several other studies showing an association with cannabis use and myocardial infarction, often with event rates anywhere from three- to fivefold higher. . . . I think we have to pay attention to this signal.”

More broadly, he continued, “we have to know that cardiovascular disease is still the number one killer in the US, and it is important for patients to think about any possible reversible risk factor. For some individuals, that’s diet and smoking or high blood pressure. And for some individuals, that may be the use of cannabis. If someone’s goal is to lower their risk of cardiovascular disease, my advice certainly would be to avoid cannabis use.”

This is particularly relevant to patients he sees as a preventive cardiologist who have a family history or other underlying risk factors, he added, suggesting that the greatest risk posed by cannabis may be among people in their 30s and 40s, though the study didn’t divvy up results by age.

Moreover, Blankstein stressed that his own research has shown patients aren’t just at risk of experiencing an MI if they use cannabis, they’re also at risk of worse long-term outcomes thereafter. In these scenarios, “it’s an opportunity now to be more aggressive in [secondary] prevention,” he said. “So I tell people: ‘It’s always best to avoid your heart attack in the first place. But if you’re already in a situation where you’ve experienced an event, it’s never too late to look forward and say: what can I do to lower my risk of future events?’”