• Posted May 29, 2025

Marijuana Use Linked to Early Signs of Heart Damage

THURSDAY, May 29, 2025 (HealthDay News) — Smoking or eating marijuana on a regular basis may damage a healthy person's blood vessels much like tobacco does, a small study finds.

Researchers from the University of California, San Francisco (UCSF) looked at the blood vessels of 55 people between 18 and 50 years old. Some smoked marijuana or ate THC-laced edibles at least three times a week for a year, while others didn't use cannabis at all, CNN reported.

None used tobacco or vapes, and they had little exposure to secondhand smoke.

“We found that vascular function was reduced by 42% in marijuana smokers and by 56% in THC-edible users compared to nonusers,” lead author Dr. Leila Mohammadi, an assistant researcher in cardiology at UCSF, told CNN.

For the study — published May 28 in JAMA Cardiology — her team used ultrasound to test how well arteries in participants' arms widened after blood flow was cut off with a tight cuff for five minutes. 

Arteries that can’t widen properly may be an early sign of blood vessel damage, which raises the risk for heart attacks, stroke and other health problems later in life.

“We’re looking at a window in the future, showing the early changes that may explain why smoking marijuana has been linked to later heart disease,” senior study author Matthew Springer, a professor of medicine at UCSF, said. “It appears the act of smoking and the THC itself both contribute to those changes in different ways.”

THC, shorthand for tetrahydrocannabinol, is what makes cannabis users high.

And even those who didn’t smoke but used THC-laced edibles regularly, showed reduced vascular function. 

That was a surprise, Dr. Andrew Freeman, a cardiologist at National Jewish Health in Denver who reviewed the findings, told CNN.

“Could it be that other forms of marijuana — teas, tinctures, edibles — are perhaps not as benign as we once thought?” he said. “We need larger studies to make a better conclusion about this finding.”

Study participants who used marijuana more often tended to have worse vascular function, suggesting a dose-related effect. However, the study didn’t show blocked arteries or plaque buildup. 

Instead, "the vessels just don’t grow in diameter in real time when they need to pass more blood, indicating an unhealthy vessel wall that presages later cardiovascular disease,” Springer explained.

In lab tests, researchers also found that blood from marijuana smokers caused cells lining vessels to release 27% less of a chemical called nitric oxide that helps relax and widen them.  CNN reported. 

Earlier research found a 39% drop in nitric oxide when cells were exposed to blood from tobacco smokers. 

Blood from edible users didn’t have the same effect.

Springer said these findings suggest that both THC and tobacco smoke itself may play a role in harming the heart as well as blood vessels.

“You do yourself no favors by switching from smoking tobacco to marijuana," he said. "Smoking marijuana just gives you a double hit — the smoke and the THC.”

Because of the potential harm it can do, the American Heart Association advises people to avoid smoking or vaping any substance, including cannabis. Its 2020 guidance also noted that irregular heart rhythms, such as atrial fibrillation, can happen within an hour of smoking THC.

More research is needed to understand whether non-smoked cannabis options could be safer. 

“In people, there’s like a Goldilocks zone for everything — too much doesn’t do right, too little doesn’t do right, but just right does fine,” Freeman concluded. “We need further investigations to see if there is a Goldilocks zone to be found.”

More information

The U.S. Centers for Disease Control and Prevention has more on cannabis and heart health.

SOURCE: CNN, May 28, 2025