Cannabis users face increased heart attack risk around surgery

As marijuana use becomes more common and legal in most U.S. states, patients who use cannabis may face a significantly higher risk of heart attack around the time of surgery, while also showing an unexpected lower risk of dangerous blood clots in the veins, suggests a study presented at the ANESTHESIOLOGY^® 2026 annual meeting.

Our findings show that it is vitally important to tell your anesthesiologist before your procedure if you use marijuana, whether for medical or recreational purposes. This is not about judgment; it is about safety. Cannabis can affect your heart, your blood vessels and how your body responds to anesthesia. Knowing about a patient's cannabis use allows the anesthesiologist to take extra precautions to keep patients safe during and after surgery."

Nader D. Nader, M.D., Ph.D., FASA, lead author of the study and professor of anesthesiology and surgery at the Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, New York

Reviewing five studies including data from 44,312 surgical patients, the authors found cannabis use was associated with a 46% increased risk of myocardial infarction, or heart attack, during or shortly after surgery compared to non-users. They found no significant links between cannabis use and stroke, respiratory failure, acute kidney injury or death.

In a surprising finding, researchers found cannabis use was associated with a 22% lower risk of venous thromboembolism, or blood clots, in the veins. The authors said this finding highlights the complex effects of cannabis on the heart and blood vessels and warrants further study.

Researchers cautioned that the lower blood-clot risk does not establish that cannabis has a protective effect. Cannabis acts on receptors in the body that may influence inflammation and clotting in different ways. More information is needed to understand the links between cannabis use, heart attacks and blood clots around the time of surgery, according to the authors.

Tetrahydrocannabinol (THC), the main psychoactive component in cannabis, can increase heart rate, blood pressure and the heart's need for oxygen, researchers said. It may also trigger spasms in the arteries that supply blood to the heart. Together, these effects can increase the risk of a heart attack, particularly during the physiological stress of anesthesia and surgery.

Patients should not assume marijuana is harmless because it is legal or plant-derived, the study authors note. Cannabis use can pose significant risks during anesthesia and surgery, potentially compromising patient safety.

Patients who use cannabis should tell their anesthesiologist and surgical team how often they use it, what form they use and when they last used it. That information will affect decisions about cardiovascular monitoring, the anesthetic plan, blood-thinning medications or whether an elective procedure should be delayed.

"Today's cannabis products are far more potent than they were decades ago, and higher THC levels can have serious cardiovascular effects," said study co-author Rose Berkun, M.D., FASA, associate professor of anesthesiology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, New York. "Educating patients about these risks and encouraging them to disclose cannabis use to both their surgeon and anesthesiologist before surgery are important steps in helping to provide the safest possible care."