The interaction between cannabis use and weight/weight management is a complicated and evolving discussion.  At the surface, the knee-jerk reaction is to assume that cannabis (and the subsequent "munchies") is the fastest way to long-term weight gain.  This makes it difficult to treat pain in the population often burden by it.  The research, however, does not support this direct and "obvious" link.  In fact, the third National health and examination survey (NHANES) study showed that in chronic heavy users of cannabis, BMI was typically lower even when controlling for other variables such as age, gender, education, caloric intake, and cigarette smoking.  This suggests that long-term changes may occur that offset short-term appetite stimulation that is characteristic of cannabis.

Cannabis is being increasingly used as 1 component of a multimodal pain control regimen since it does not have the same risk of overdose and abuse potential seen in opioids, and has a novel mechanism that complements other commonly used pain medications without dangerous interactions.  Moreover, it is often used to assist in falling asleep without some of the risks of certain prescription sleep medications.  On top of this, some C8 as a "natural" treatment for these conditions and others.  Unfortunately for many users, it is also disqualifying factor when when attempting to be approved for weight loss surgery.

A recently published systematic review (Jung et al, " effects of perioperative cannabis use on bariatric surgical outcomes: A systematic review") compiled research articles that evaluated the use of cannabis in the perioperative period in patients undergoing bariatric surgery.  The studies demonstrated that approximately 10% of patients use cannabis in perioperative period.  For comparison, tobacco products are used by approximately 37% of noncannabis users and 26% of reported cannabis users in the studies, despite tobacco use having known negative effects on healing after surgery due to its effects on blood vessels.  1 study included in the review found that 6-month and 12-month weight loss was significantly higher in the patients who used cannabis, although the study only included 8 patients who use cannabis whom were compared with 231 nonusers.  Additionally, the 2 studies included that tract postoperative complications found no significant difference in minor or major complications within 90 days.

Assuming these data are representative of the general population of patients undergoing bariatric surgery who use cannabis, use should not preclude qualification for surgery.  Not only were outcomes better, but use did not impact negative outcomes in any way. There are number of reasons why this may have been the case.  First, one common adverse effects shortly after bariatric surgery is abdominal pain/nausea and poor food intake.  Low protein intake after bariatric surgery increases the risk of worse outcomes, as protein is a necessary component for recovery from surgery.  As cannabis has known antinausea and appetite stimulating properties, this may help maintain adequate food intake after surgery.  Another reason is related to the study data, specifically.  Since cannabis users reported lower smoking rates in the studies, and they were typically younger and otherwise healthy, this may have created a falsely lower risk of negative outcomes.  Had these users been compared with nonusers of the same age and health status, it is feasible that outcomes would be different.  On the other hand, even if weight loss and adverse effects were equal between users and non users, long-term potential benefits for cannabis use in quality of life remains, considering its utilization for pain, sleep, and other comorbidities. On a final note, cannabis use has also been shown to decrease opioid pain medication requirements, and this could conceivably reduce negative side effects of opioids such as constipation, somnolence, and abuse potential.