Millions of Americans use marijuana for medical reasons, including easing anxiety or reducing side effects of cancer treatment. Millions more use it recreationally, saying it helps them relax.

A new study now reports that regular marijuana smokers may increase their risk of heart disease and heart attack.

Benefits and risks

There has long been debate about the benefits versus the risks of using cannabis, with evidence on both sides to support each position. For example some studies have shown taking oral cannabinoids can help people cope with the nausea brought on by chemotherapy. Other studies have shown that regular use of marijuana can cause problems such as marijuana use disorder, a condition where the user is showing physical or psychological problems but has difficulty controlling or reducing their use of cannabis.

Now this latest study, from researchers at Stanford Medicine,  shows that THC, the psychoactive part of the drug, can cause inflammation in endothelial cells. These are the cells that line the interior of blood vessels. When these cells become inflamed it can cause a constriction of the vessels and reduce blood flow. Over time this can create conditions that increase the risk of heart disease and heart attack.

Assessing the risks

The study included people who reported smoking marijuana, and about 11,000 smoked more than once a month. Regular marijuana smokers:

• Were significantly more likely to have a heart attack.

• Were more likely to have their first heart attack before age 50, increasing the risk of additional attacks.

The team then used the iPSC method to create human endothelial cells and found that THC promoted inflammation in these cells. They also saw early signs of atherosclerosis, including fat and plaque buildup in artery walls.

Not harmless

In a news release, Dr. Wu, the study’s lead author, said: “There’s a growing belief that marijuana is harmless. Marijuana has important medical uses, but recreational users should be cautious about heavy use.”

The team also found that genistein, a natural compound in soy and fava beans, prevents THC‑related damage. Their Cell study showed that genistein blocks THC’s harmful cardiovascular effects without interfering with its beneficial neurological effects.

“As more states legalize recreational marijuana, users should know it may cause cardiovascular side effects,” said Dr. Wu. “Genistein reduces THC‑induced endothelial damage without blocking its central nervous system effects, and it may help medical marijuana users protect their heart health.”

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