CALIFORNIA – A recent study from the University of California, San Francisco (UCSF) has highlighted new concerns about the impact of cannabis on heart health. The research shows links between cannabis use, both smoked and eaten as edibles, and early signs of heart disease.

Dr. Leila Mohammadi and Professor Matthew Springer from UCSF’s Division of Cardiology led the research. Their team is the first to examine how tetrahydrocannabinol (THC), the active ingredient in cannabis, affects blood vessel function in humans.

The data suggest that people who use marijuana, whether by smoking or eating THC edibles, experience significant drops in blood vessel performance, a key measure for heart and vascular health. Blood vessel function fell by 42% in marijuana smokers and by 56% in edible users compared to nonusers. These numbers point to a possible higher risk from edibles.

Professor Springer explained that the study offers an early look at changes in the blood vessels. These signs could help explain previous links between marijuana use and later heart problems. Both the act of smoking and the THC compound itself seem to play roles in these changes.

Researchers studied 55 adults aged 18 to 50, dividing them into three groups: regular marijuana smokers, THC-edible users, and those who did not use marijuana. Participants did not smoke tobacco or use vapes, and had little exposure to secondhand smoke.

Cannabis Can Harm Blood Vessels

This allowed the research team to focus on the effects of marijuana alone. Using ultrasound, the team measured how well the arteries could widen after a short blockage of blood flow. This reaction relies on the release of nitric oxide, which is important for healthy blood vessel function.

The team also tested how blood serum from the participants affected endothelial cells, which line the inside of blood vessels.

Results showed that marijuana smokers had blood serum that reduced nitric oxide production by 27%, similar to what is seen in tobacco smokers, who had a 39% drop. In contrast, the serum from THC-edible users did not show this effect on nitric oxide.

This suggests that while both smoking and eating THC can harm blood vessels, they may do so through different processes. Dr. Mohammadi said the way THC affects blood vessels when eaten is still not clear, but it does not appear to involve serum changes.

Dr. Andrew Freeman, a heart disease expert at National Jewish Health in Denver who was not involved in the research, called the findings about edibles unexpected. He stressed the need for larger studies to fully understand these results.

Use Growing Among Americans

The issue is growing as more Americans use marijuana. The National Survey on Drug Use and Health reports that one in five people over age 12 used marijuana in the past year. With medical cannabis now legal in 38 states and recreational use allowed in 24, experts are concerned that public attitudes about cannabis safety are moving ahead of science.

Previous studies back up these concerns: daily marijuana use was linked to a one-third higher risk of coronary artery disease in 2023, and to a 25% higher risk of heart attack and 42% higher risk of stroke in 2024.

Professor Springer made clear that this research shows a link, not proof that marijuana causes poor blood vessel function. But the findings did show heavier marijuana use matched with worse vascular health. This pattern matches earlier studies in mice, which found that marijuana smoke can limit blood vessels’ ability to send oxygen to the body’s organs.

The American Heart Association has long advised against smoking or vaping anything, including marijuana, due to risks to heart, lung, and blood vessel health. The UCSF study supports this advice, especially for young adults who may not think they are at risk of heart disease.

Robert Page, a professor at the University of Colorado Skaggs School of Pharmacy, said the results should encourage doctors to talk with patients about marijuana use, especially those who already have heart conditions.

Cannabis Speeds up Blood Pressure

People with a history of heart disease may face even greater risks. THC can speed up the heart and raise blood pressure, which could make coronary artery disease worse. Dr. Peter Grinspoon, a cannabis researcher at Harvard Medical School, advised caution for people who have recently had a heart attack.

As cannabis use becomes more common, experts encourage people to consider these risks. Dr. Joseph Wu, a co-author of the study, pointed out that legalization does not mean a product is safe. While edibles avoid the harmful byproducts from smoking, like carbon monoxide and certain hydrocarbons, the new study suggests edibles may still harm the heart through the effects of THC.

The research team says more large and long-term studies are needed to confirm these findings and to understand exactly how THC affects the heart. For now, the UCSF study gives a clear warning: marijuana, whether smoked or eaten, may not be as safe as some believe. As Professor Springer summarized, blood vessels do not seem to distinguish between smoke from tobacco or marijuana.