Because marijuana use has become legal for medical and recreational purposes in many states, Dr. Zafar says she is encountering more patients who use it.
“What’s confounding about marijuana is that it comes in many different formulations. It can be smoked, vaped, or it can be an edible. Some people are on medical marijuana, and it's prescribed,” Dr. Zafar says. “And marijuana today has a much higher portion of THC [tetrahydrocannabinol, the psychoactive ingredient in marijuana that produces a high] than it used to, which makes it more potent.”
There are also cannabidiol (CBD) supplements, often in the form of chewable gummies, notes Dr. Zafar. CBD is a chemical found in marijuana that does not contain THC.
All these different formulations can make it difficult for an anesthesiologist to plan around, Dr. Zafar says. “We want patients to tell us what form of marijuana—and how much—they are using, so we can understand the potency,” she says. "This is important because it can affect how well the anesthesia works. You may actually have more of a tolerance to anesthesia, which means you need more of it.”
While doctors continue to research the effects of marijuana and CBD on a patient’s surgical risks and their recovery, the American Society of Anesthesiologists says enough is known to warrant certain precautions before and after surgery. For example, patients are advised not to use any marijuana product on the day of surgery.
If a patient does smoke on the day of surgery, it should be at least two hours before the procedure, according to the American Society of Regional Anesthesia and Pain Medicine, because smoking marijuana can “significantly increase heart rate and blood pressure within the two hours following use, and it may increase the patient’s risk of suffering a surgery-related heart attack.”
It's also unclear when it’s safe to resume marijuana use following surgery. “It can depend on the patient’s medical history and the type of surgery they had,” says Dr. Zafar.