*This article first appeared on SFGATE
Researchers at UC San Francisco published a study Wednesday that found troubling cardiovascular risks linked to using cannabis, even for people who avoided smoking cannabis entirely.
The study tested 55 people from the Bay Area to see if their cardiovascular function was different depending on whether they used smoked cannabis, used cannabis edibles or abstained from cannabis entirely. The research found that regular cannabis users — both edible users and cannabis smokers — had reduced cardiovascular function and increased risk of developing premature heart disease.
The study joins a growing body of evidence that chronic cannabis use could be damaging cannabis users’ cardiovascular system. A 2024 study evaluating survey data found that daily marijuana use was associated with a 25 percent increase in risk of heart attack and a 42 percent increased risk of stroke, but this is one of the first studies that measured cardiovascular function in healthy adults who strictly used cannabis edibles without smoking, according to UCSF researcher and lead author Leila Mohammadi.
The findings that even people using only THC edibles without smoking still showed signs of cardiovascular damage surprised Matthew Springer, a UCSF researcher and another author on the study. Edibles have been seen as possibly less likely to damage the heart, according to a 2020 recommendation by the American Heart Association.
“When I first saw the THC result, I said to Leila, ‘Scientifically, this THC result is really interesting but boy does it screw up the public health messaging,’” Springer said.
The UCSF study tested cardiovascular function with a two-part test. First, they conducted ultrasounds of an artery in each subject’s arm to see how blood flow changed after being constricted with a blood pressure cuff. The ultrasound study found that both cannabis smokers and cannabis edible users had arteries with lower dilation rates compared to people who did not consume cannabis.
The study then examined blood serum from test subjects to see how it reacted to endothelial cells, which regulate blood flow. This test found that cannabis smokers, but not edible users, produced less nitric oxide levels, which is an indicator of cardiovascular health. The drop in nitric oxide levels seen in marijuana smokers was similar to earlier research on the effects of smoking tobacco, according to the study.
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Springer said the fact that edible-only users showed signs of damage on the dilution test but not the nitric oxide test, while cannabis smokers showed damage on both tests, shows that THC alone without smoking could be directly damaging the vascular system. He said that could be evidence that smoking marijuana could be causing a “double whammy” of negative effects on heart health.
The study authors tested all subjects for nicotine exposure to make sure none of the participants used tobacco.
Taken together, these findings indicate that using THC is associated with an increased risk of developing heart disease early, according to the study.
The study did not prove a causal relationship between consuming THC and heart disease, but Springer said that because this latest study found early warning signs of heart disease in healthy subjects that confirm earlier studies, “we can be pretty confident” that cannabis use causes damage to the cardiovascular system.
Benjamin Caplan, a Massachusetts medical doctor who specializes in medical cannabis use, said in an email that the study “raises important questions” but falls short of providing “convincing evidence of cardiovascular damage from cannabis use.” Caplan said the study did not control for what specific cannabis products subjects used or their diet, body mass index, or lifestyle factors and contained only one woman in the edible group, which he said limits its generalizability.
“This study says nothing about what happens when cannabis is used thoughtfully, in low doses, under medical supervision, or as part of a broader care plan,” Caplan said. “It doesn’t reflect the patients I see — older adults tapering off opioids, cancer survivors managing pain, or anxious individuals finally sleeping through the night. It’s a narrow lens applied to a very broad subject.”
The study’s subjects were all regular users who used cannabis at least three times a week, and the cardiovascular harm was stronger for people who used more THC a week, which Springer said is a sign that even using less cannabis could spare users from the heaviest cardiovascular harm: “It really does seem like the more you take, the worse it is.”