Anesthesiologists always consider "multi-modal" approaches to pain management to minimize side effects, said Dr. Peter Yeh, an anesthesiologist at the University of California San Francisco. But in a regular, heavy marijuana user, he pays extra attention to other classes of medications, including nerve blocks or an epidural.

A small dose of the THC in cannabis reduces pain, but in high doses, it can increase it, Narouze said. The same is true for nausea. Emergency rooms have seen a growing number of patients with hyperemesis – essentially, nonstop vomiting – caused by excessive cannabis use.

Dr. Samer Narouze, president of the American Society of Regional Anesthesia and Pain Medicine said edibles increase the risk for hyperemesis because they take longer to lead to a high, so people think they haven't yet eaten enough. Smoking causes a quick high that also fades rapidly, while edibles take longer to have their longer-lasting effect. A heavy cannabis user might also miss one or two regular doses during a long surgery and recovery, leading to more pain, Narouze said.