Cannabis use may increase the risk of a heart attack during or shortly after surgery, even as researchers have identified a lower incidence of venous blood clots among users. The findings, presented at the ANESTHESIOLOGY® 2026 annual meeting in San Diego, highlight the need for patients to disclose cannabis consumption to their surgical teams before undergoing a procedure.
The study reviewed five studies involving 44,312 surgical patients and found that cannabis users had a 46% higher risk of myocardial infarction, commonly known as a heart attack, compared with non-users. Researchers, however, found no significant association between cannabis use and stroke, respiratory failure, acute kidney injury or death.
The findings come at a time when marijuana use is becoming more common and legal in most US states. Researchers said the results underline the importance of understanding how cannabis affects the cardiovascular system, particularly when the body is under the physiological stress associated with surgery and anaesthesia.
Cannabis use may increase cardiovascular risks during surgery
According to the researchers, tetrahydrocannabinol (THC), the primary psychoactive component in cannabis, can raise heart rate and blood pressure while increasing the heart’s demand for oxygen. It may also trigger spasms in the arteries supplying blood to the heart. These effects could increase the likelihood of a heart attack, particularly during anaesthesia and 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, stressed that patients should inform their anaesthesiologists about cannabis use, regardless of whether it is for medical or recreational purposes.
“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,” Nader said.
He added that the disclosure was not about judging patients but about ensuring their safety. Cannabis can influence the heart, blood vessels and the body’s response to anaesthesia, making it important for medical teams to understand a patient’s consumption habits before treatment.
Researchers also cautioned against assuming that cannabis is harmless simply because it is plant-derived or legal in a particular jurisdiction. They noted that its effects during surgery could pose risks that require additional precautions.
Rose Berkun, M.D., FASA, an associate professor of anesthesiology at the same institution and co-author of the study, pointed to the increasing potency of cannabis products.
“Today’s cannabis products are far more potent than they were decades ago, and higher THC levels can have serious cardiovascular effects,” Berkun said.
She emphasised that educating patients about these risks and encouraging them to disclose cannabis use to their surgeons and anaesthesiologists are important steps towards safer care.
Lower blood clot risk requires further investigation
Alongside the increased heart attack risk, researchers found that cannabis use was associated with a 22% lower risk of venous thromboembolism (VTE), a condition involving blood clots in the veins. Although this was an unexpected finding, the authors warned against interpreting it as evidence that cannabis protects against clot formation.
Cannabis interacts with receptors in the body that may influence inflammation and blood clotting through different mechanisms. However, the researchers said further investigation is necessary to establish how these processes relate to heart attacks and venous blood clots in surgical patients.
The study also did not identify significant associations between cannabis use and stroke, respiratory failure, acute kidney injury or death. These findings do not establish that cannabis has no effect on these outcomes, but indicate that the reviewed evidence did not demonstrate statistically significant links.
For patients preparing for surgery, the researchers recommend informing the anaesthesiologist and surgical team about how frequently cannabis is used, the form in which it is consumed and the time of the last use. Such information can help medical professionals assess cardiovascular risks, determine appropriate monitoring and make decisions about the anaesthetic plan and blood-thinning medications. Depending on the circumstances, the team may also consider delaying an elective procedure.
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Sridhar P