New Delhi: Cannabis users face a higher risk of having a heart attack during or after surgery, found a new study. However, they might also have a lower risk of developing blood clots in their veins.
The findings were presented at the American Society of Anesthesiologists’ ANESTHESIOLOGY 2026 annual meeting. For their analysis, researchers reviewed five studies involving 44,312 patients who had undergone surgery. They found that cannabis users had a 46 per cent higher chance of having a heart attack than those who did not use the drug.
“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,” lead author Nader D Nader, professor of anesthesiology and surgery at the Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, said in a statement.
The data also revealed that cannabis users were associated with a 22 per cent lower risk of venous thromboembolism (VTE), a condition where blood clots form in the veins. However, researchers warned that this is just an association and does not mean that cannabis can prevent blood clots.
Also read: Scientists found a strange correlation — small babies, worse math scores
How cannabis affects the heart
Tetrahydrocannabinol (THC), the main compound in cannabis, can increase heart rate. Consuming the product also makes the heart demand more oxygen, which can lead to spasms in the arteries that supply blood to the heart. The drug essentially acts on the body’s receptors influencing inflammation and clotting.
According to the researchers these effects can increase the risk of a heart attack, especially during surgery, when the body is already facing the stress of the procedure and the anesthesia. To reduce the adverse risks, doctors urge patients to inform their anaesthesiologists about their cannabis use before they undergo any procedure.
With that additional information, medical teams could closely monitor a patient’s heart and better manage medications, including blood thinners, when required. In some cases, procedures could also be postponed to make sure they are safer for the patient.
“Today’s cannabis products are far more potent than they were decades ago, and higher THC levels can have serious cardiovascular effects. 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,” said study co-author Rose Berkun, associate professor of anesthesiology, in a statement.