What Cannabis users should know about Anesthesia

Going under the knife any time soon? Then expect to be asked about your cannabis use at some point by your anesthesiologist. At the beginning of 2023, the American Society of Regional Anesthesia and Pain Medicine (ASRAPM) published provisional guidance for its members on how to work with their cannabis-using patients during perioperative care (“perioperative” is the period of medical care in preparation for, during and just following an operation). In these guidelines, anesthesiologists are urged to question patients “about cannabinoid use, dose and frequency, route of administration, and time of last use.” For as anesthesiologists have learned over the years, cannabis users don’t go under as easily as those who don’t. And unless you want your surgical or dental procedure to hurt more than it already will, it makes sense to answer truthfully.

Simply put, cannabis-using patients need a lot more anesthesia than those who don’t partake. No one is certain whether it’s specifically THC, CBD or any other combination of factors that’s to blame for it. But its effect is clear: if you’re smoking or using regularly, you’ll need three times as much of the common sedative propofol to give adequate coverage for an endoscopy. After the operation, a 2018 study found higher pain scores and opioid use amongst cannabis users during recovery than the group that didn’t consume. So why is this the case? Here's what is known.

First, as anyone who uses cannabis for chronic pain knows, cannabis can impact pain perception. However, because medical cannabis use is not standardized, people “may use doses and formulations that lead to greater adverse effects, including alterations in pain and responses to opioids,” according to ASRAPM. This can result in improper dosing of anesthesia and pain management medications if the doctor is unaware, leading to under-treatment of pain or even overdose, not to mention the risk of opioid use disorder because the patient has to use more medicine to compensate.

Another concern is the effect that cannabis has on respiratory function. Cannabis use is known to cause a decrease in respiratory rate and a reduction in lung function, which can result in respiratory depression, a common side effect of many anesthetic drugs. ASRAPM cites two studies in its guidelines, one examining CBD and the other with co-usage of THC and opioids. However, they acknowledge that more research is needed, and the level of certainty over safety is low.

Cannabis use can also impact cardiovascular function, causing an increase in heart rate and a decrease in blood pressure. For those with heart disease, this can be especially alarming. Some susceptible patients might even suffer a heart attack from the added stress on their system.

Furthermore, cannabis can also impact a patient's mental state. For most users, this is the point; surgery, after all, is a stressful procedure, so some people may reason, why not use something that can calm you down beforehand? However, because of all the complications that can arise during or after surgery, it’s just not a good bet.

Hopefully, we’ve convinced you to get good medical advice around this issue. Because every person going into surgery has their own unique medical history, generalizations around this topic are impossible to make. However, the Mayo Clinic saw fit to make this recommendation on their site: “Marijuana has a central nervous system (CNS) depressant effect. As a result, marijuana use in combination with anesthesia or other drugs used during or after surgery might cause an additive effect. Don't use marijuana two weeks before planned surgery.” Consult your doctor about how long you may have to wait before you pick it up again. No matter how long it may be, just remember it will be waiting for you on the other side of your recovery.