Abstract Background Pre-clinical studies indicate increased food intake and weight gain as cannabinoid effects. Cross-sectional epidemiological studies, however, indicate lower prevalence of obesity among cannabis users. Here, we aim to study the weight-gain research question in the prospectively conducted National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Methods NESARC was designed to produce nationally representative estimates for the US population. Participants (aged 18+) completed computer-assisted personal interviews on cannabis use, body weight and height at Waves 1 (W1, 2001–02) and 2 (W2, 2004–05). General linear modelling yields estimates for change in body mass index (BMI) regressed on cannabis-use status, with covariate...