Abstract Body: Introduction: Literature on cannabis use among adolescents and body mass index (BMI) is mixed; some but not all studies show a negative association between cannabis use and BMI. Yet, studies in adults show a consistent negative association between cannabis use and BMI. Therefore, we investigated associations between cannabis use and body mass index z-scores (BMI Z-scores) among adolescents. Hypothesis: We hypothesized that cannabis use in the past year is associated with lower BMI Z-scores in adolescents. Methods: Children of the Nurses’ Health Study II ages 9 to 14 in 1996 were recruited to participate in the Growing Up Today Study (GUTS 1). The GUTS 1 cohort investigated how diet and exercise influence weight changes over the lifecycle. This analysis included participants who had at least one BMI Z-score between the ages of 12 and 20 during the years in which cannabis use was assessed, 1999, 2001, 2003, and 2005; at the 1999 survey, participants were 12-17 years of age. Cannabis use was assessed with the question “Have you ever used marijuana in the past year.” Cannabis use was coded into a binary variable of yes/no. Self-reported weight and height were used to calculate BMI Z-scores for age. We used a linear mixed model with a random effect for participant ID to assess if cannabis use in the past year was associated with BMI Z-scores, and adjusted for age, sex assigned at birth, sexual orientation, cigarette smoking, alcohol use, physical activity, and sibling in the study. Missing data was handled with the missing indicator method. Results: A total of 13,432 participants had at least one BMI Z-score and contributed 30,756 observations in the model. In 1999, past year cannabis users (n=1128) had a mean age of 15.8 years, tended to smoke cigarettes (75.1%), met physical activity guidelines of 7+ hours of moderate to vigorous activity/week (77.2%) and consumed alcohol (68.1%). In 2005, past year cannabis users (n=2848) had a mean age of 20.5 years, tended to smoke cigarettes (68.2%), met physical activity guidelines of 7+ hours of moderate to vigorous activity/week (52.7%) and consumed alcohol (88.4%). Adjusting for age and natal sex, cannabis use was not associated with BMI Z-scores (b: 0.030; 95% CI: -0.010, 0.070 p=0.14) and was not materially different in the fully adjusted model (b: 0.026; 95% CI:-0.022 ,0.073; p=0.28) Conclusions: Among the GUTS 1 cohort, past year cannabis use was not associated with differences in BMI Z-scores among adolescents