TPS 771: Diet and lifestyle, Exhibition Hall, Ground floor, August 26, 2019, 3:00 PM - 4:30 PM Background/Aim: Several epidemiological studies have reported positive associations between marijuana use and adverse cardiovascular effects, yet there is insufficient evidence to draw definitive conclusions. Few studies have been performed to examine the possible biological mechanisms responsible for this observation. In this study, we examined whether current marijuana use is associated with elevated serum levels of gamma glutamyl transferase (GGT), a biomarker of oxidative stress that is linked to cardiovascular disease risk. Methods: We combined questionnaire data with laboratory measurements (GGT and cotinine) in serum samples available for adults aged ≥ 18 years participating in the US National Health and Nutrition Examination Survey during 2005 to 2014. We categorized the participants into 496 exclusive current cigarette smokers (self-reported cigarette smoking within the five days prior to examination, but neither used marijuana nor any other tobacco products), 105 recent exclusive marijuana users (self-reported use of marijuana within the five days prior to examination but never used any tobacco products) and 2524 nonusers (neither used any tobacco nor marijuana products in life). We performed comparative analyses of the adjusted geometric means (aGMs) of GGT among those groups using multiple regression models, adjusted for age, gender, race/ethnicity, body mass index, education, poverty-income ratio, fasting length, serum cotinine and average alcohol drinks/day. Results: Recent exclusive marijuana users had a small but significantly higher aGM of GGT (23.4 u/L, 95% confidence interval, CI: 20.3, 27.0 u/L) compared to nonusers (20.0 u/L, CI: 19.0, 21.1 u/L) (p=0.046). Cigarette smokers had the highest aGM of GGT (30.2 u/L, CI: 24.3, 37.6 u/L) among these groups. Conclusions: The findings suggest a plausible biological pathway for effects of exclusive marijuana use on cardiovascular disease risk. Future studies are needed to confirm these findings and to better examine the health effects of marijuana in the environment of liberalized use.