Patients who use cannabis may face a higher risk of heart attack during or shortly after surgery, according to a research review presented at the ANESTHESIOLOGY 2026 annual meeting. The finding is an association rather than proof that cannabis causes the events, but it reinforces the importance of discussing cannabis use with an anesthesiologist before a procedure.
The review combined data from five studies involving 44,312 surgical patients. Across those studies, cannabis use was associated with a 46% higher risk of myocardial infarction, commonly called a heart attack, during or shortly after surgery compared with nonuse. The researchers found no significant association with stroke, respiratory failure, acute kidney injury or death.
An additional result complicates the picture. Cannabis use was associated with a 22% lower risk of venous thromboembolism, a term covering blood clots in the veins. The researchers explicitly cautioned that this observation does not show cannabis protects against clotting. More research is needed to understand both findings and the biological mechanisms behind them.
A perioperative question for patients and clinicians
The period surrounding surgery places unusual demands on the heart and circulation. Anesthesia, the procedure itself, pain, fluid changes and recovery can all alter how the body responds. Cannabis may add another variable because its active compounds can affect cardiovascular function and the body’s response to anesthesia.
According to the researchers, tetrahydrocannabinol, or THC, the primary psychoactive compound in cannabis, can raise heart rate, blood pressure and the heart’s oxygen demand. Those effects may be especially relevant when a patient is already undergoing the physiological stress of an operation.
Lead author Nader D. Nader, a professor of anesthesiology and surgery at the University at Buffalo’s Jacobs School of Medicine and Biomedical Sciences, said disclosure is about patient safety rather than judgment. Knowing whether a patient uses marijuana for medical or recreational reasons can help an anesthesia team take appropriate precautions before, during and after an operation.
That practical message is straightforward: patients should tell their anesthesiologist about cannabis use. The supplied report does not prescribe a specific waiting period before surgery, nor does it establish a universal change in care. Instead, it supports having an accurate conversation early enough for the clinical team to consider the information in the context of the planned procedure and the patient’s overall health.
What the numbers do—and do not—show
The 46% figure is a relative increase in risk observed in the reviewed studies. It should not be read as a prediction that any individual cannabis user will have a heart attack around surgery. Absolute risk depends on many factors that are not detailed in the supplied report, including the type of surgery, a patient’s age, existing cardiovascular disease and other clinical circumstances.
Likewise, the review’s design limits what can be concluded about causation. The study evaluated associations across previously available studies. It cannot on its own separate cannabis use from every other characteristic that might differ between users and nonusers, and it cannot determine which patterns of use, products or doses may be most relevant.
That uncertainty is particularly important because cannabis is not a single, uniform exposure. Products can vary in THC content and other compounds, and patients may use them for different reasons. The source report does not provide evidence that one route of use or type of product is safer than another in the perioperative setting.
The unexpected clotting result
The lower observed rate of venous thromboembolism is not a green light for cannabis use before surgery. The researchers said the result highlights the complex ways cannabis may interact with inflammation and clotting. It is a signal worth studying, not evidence of a protective therapy.
Venous thromboembolism includes clots that form in veins and can become dangerous if they travel through the body. Surgery itself is a setting where clinicians consider clot risk carefully. A finding from an observational evidence review should not override established prevention and treatment decisions made by a patient’s care team.
The apparent contrast between a higher associated risk of heart attack and a lower associated risk of venous clots is one reason the researchers call for more work. Cardiovascular risk is not a single process. Heart attacks, blood pressure changes, heart rate, inflammation and venous clotting involve related but distinct mechanisms. Future studies will need to clarify whether the observed patterns are reproducible and, if so, why they occur.
How to use the findings now
The study is best understood as a safety signal for perioperative care, not as a reason for patients to make abrupt medical decisions without professional advice. People preparing for surgery can help their clinicians by sharing a complete medication and substance-use history, including medical or recreational cannabis. That gives the anesthesiology and surgical teams the information they need to assess potential risks and plan care.
The findings also matter as cannabis becomes more common and legal in many US states. Legal availability does not eliminate the need to account for possible interactions with surgery and anesthesia. A routine preoperative discussion should leave room for cannabis use without stigma, because incomplete information can make safety planning harder.
For researchers, the next step is more precise evidence: studies that can examine timing, frequency and form of cannabis use, as well as patient and procedure differences. Until then, the review provides a cautious conclusion. Cannabis use was associated with greater perioperative heart-attack risk in the available data, while the surprising clotting observation remains unresolved and should not be treated as evidence of benefit.
This article is based on reporting by Medical Xpress. Read the original article.
Originally published on medicalxpress.com
