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The Effect of Marijuana use on Weight Loss and Comorbidity Remission after Bariatric Surgery. John Hammond, Raymond Sun, Lindsay Janes, Alma Torres, Jonathan Finks, MD, Associate Professor of Surgery. University of Michigan Medical School

Background: Marijuana use has become increasingly common among patients seeking bariatric surgery. However, little is known about its effect on weight loss or associated outcomes of bariatric surgery, an important question given the orexigenic nature of the drug. We sought to compare patient reported outcomes on annual surveys among users and non-users of marijuana undergoing bariatric surgery in Michigan.

Methods: We examined data from the Michigan Bariatric Surgery Collaborative to identify patients who had undergone bariatric surgery between 2014 and 2018 and had answered a recently added survey question on marijuana use. We used multivariable linear and logistic regression models to compare risk-adjusted weight loss and comorbidity remission between patients who did and did not use marijuana. Comorbidity remission was defined as discontinuation of therapy for the condition among patients treated for the condition at baseline. Statistical models were adjusted for patient characteristics and procedure type (gastric bypass, sleeve gastrectomy, adjustable gastric band and duodenal switch). Follow-up ranged between 1 and 5 years (mean 2.5 years).

Results: Among 1736 study patients, 101 (6%) used marijuana with 68% of those reporting daily or weekly use and 75% using an inhaled form. Marijuana users had a similar procedure mix and comorbidity profile to non-users but tended to be younger (43 vs. 48 years, p<0.0001), less likely to have private insurance (68% vs. 78%, p=0.0213), more likely to smoke cigarettes (20% vs 7%, p<0.0001), and have a history of alcohol use disorder (17% vs. 9%, p=0.0290). Marijuana users also scored higher (worse) on the AUDIT-C survey measuring alcohol consumption (1.4 vs. 0.9, p=0.0390). Marijuana users had modestly higher adjusted mean percent total weight loss (31% vs. 28% p=0.0215), but no significant difference in adjusted reduction in body mass index (15 vs. 13 kg/M2, p=0.0501). Additionally, marijuana use did not impact adjusted rates of discontinuation of insulin (68% vs. 69%, p=0.8560), oral hypoglycemics (82% vs. 74%, p=0.4525), antihypertensives (56% vs. 57%, p=0.8282), lipid-lowering medications (46% vs. 61%, p=0.2611) or CPAP/BiPAP (82% vs. 65%, p=0.0847).

Conclusions: Marijuana was used by a small proportion of bariatric surgery patients but was associated with higher rates of tobacco and alcohol consumption, suggesting a need for substance abuse counseling in these patients. However, marijuana use did not affect weight loss or comorbidity remission for up to five years after bariatric surgery. Further study will be needed to assess the effect of marijuana use on long-term outcomes with bariatric surgery.