A new study has raised fresh concerns about cannabis use, suggesting that both smoking weed and eating THC-laced edibles may harm blood vessels and lead to early signs of heart disease.
Researchers from the University of California, San Francisco, say they’ve seen troubling changes in how blood vessels work in regular cannabis users. And these changes look a lot like what’s seen in people who smoke tobacco.
“It’s a warning sign,” said Prof Matthew Springer, the senior author of the study. “We’re seeing early signs of damage that could lead to heart disease later on.”
The research, though small in size, is one of the first to look at how THC—the active compound in marijuana—affects the human cardiovascular system. And the results are likely to stir debate as cannabis use grows across the world.
What the Study Found
The study followed 55 healthy adults aged 18 to 50. They were split into three groups: those who regularly smoked marijuana, those who used THC edibles, and those who didn’t use cannabis at all.
None of the participants smoked tobacco, vaped, or had high exposure to second-hand smoke.
Ultrasounds showed that blood vessels in the arms of weed smokers and edible users didn’t widen as much as they should after being squeezed with a pressure cuff. That’s a key sign the vessels are not functioning properly.
“Vascular function was reduced by 42% in marijuana smokers and 56% in edible users compared to nonusers,” said Dr Leila Mohammadi, the study’s lead author.
This effect—where blood vessels fail to expand as needed—is linked to a higher risk of future heart attacks and strokes, doctors say.
It’s Not Just the Smoke
The results also surprised some experts. Damage wasn’t just seen in those who smoked. Even people who consumed cannabis in edible form—no smoke involved—showed signs of poor vascular health.
That caught the attention of Dr Andrew Freeman, a heart specialist at National Jewish Health in Denver.
“Could it be that teas, tinctures, and edibles aren’t as harmless as we thought?” Freeman asked. “We definitely need bigger studies to confirm this.”
Not Proof, But A Clear Warning
Researchers are careful to say this study does not prove cannabis causes heart disease. It only shows a link between regular use and signs of early trouble.
Still, they say the results are worth paying attention to—especially as cannabis becomes more widely used and accepted.
A separate part of the study looked at how the blood of cannabis users affected lab-grown cells. Blood from weed smokers led to a 27% drop in the cells’ ability to produce nitric oxide, a chemical that helps blood vessels relax and stay healthy. That mirrors what’s seen with tobacco smokers.
Interestingly, blood from edible users didn’t have the same effect in the lab, even though their blood vessels in real life also showed problems. That finding leaves some unanswered questions.
The Bigger Picture
This isn’t the first study to raise alarms. In 2024, a major study found that daily cannabis users had a 25% higher risk of heart attack and a 42% higher risk of stroke. Even people with no history of heart disease were affected.
And last year, a separate study found that daily cannabis use could raise the risk of coronary artery disease by one-third.
The American Heart Association has advised people not to smoke or vape cannabis, citing possible harm to the heart and lungs. In a 2020 report, the group warned that THC can cause irregular heart rhythms within an hour of smoking.
Experts Call for More Research
Despite the growing body of evidence, much remains unknown. “We’re only scratching the surface,” Springer said.
There are also still questions about whether there’s a safe way to use cannabis, or whether some products are less harmful than others.
“In people, there’s like a Goldilocks zone,” said Freeman. “Too much is bad, too little might do nothing—but maybe there’s a just-right dose that’s safe. We just don’t know yet.”
For now, experts say the message is simple: If you care about your heart, don’t assume cannabis is risk-free.
“You don’t do yourself any favours by switching from tobacco to marijuana,” said Springer. “In fact, you might be giving your body a double hit—the smoke and the THC.”
