Cannabis Use Linked to Higher Heart Attack Risk During and After Surgery, but Fewer Blood Clots

SAN DIEGO - 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," said 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. "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."

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."

*** ANESTHESIOLOGY 2026 news releases may contain updated data that was not originally available at the time abstracts were submitted.

THE AMERICAN SOCIETY OF ANESTHESIOLOGISTS
Founded in 1905, the American Society of Anesthesiologists (ASA) is an educational, research and scientific society with more than 62,000 members organized to advance the medical practice of anesthesiology and secure its future. ASA is committed to ensuring anesthesiologists evaluate and supervise the medical care of all patients before, during and after surgery. ASA members also lead the care of critically ill patients in intensive care units, as well as treat pain in both acute and chronic settings.

For more information on the field of anesthesiology, visit the American Society of Anesthesiologists online at asahq.org . To learn more about how anesthesiologists help ensure patient safety, visit asahq.org/madeforthismoment . Join the #ANES26 conversation on social media. Follow ASA on Facebook , X , Instagram , Bluesky and LinkedIn .

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