Are cannabis users less likely to gain weight? Results from a national 3-year prospective study

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 adjustment based on a conceptual model for BMI determinants (n = 33 000). Results At W2, 77% of the participants never used cannabis, 18% had discontinued use (‘quit’), 3% were initiates and 2% were persistent users. Estimated W1-to-W2 BMI change shows an increase for all subgroups. Compared with never-users (reference), inverse slope estimates and attenuated change (%) in BMI between W1 and W2 are seen for cannabis-use subgroups: quitters [β = –0.81; 95% confidence interval (CI) = –1.01, –0.60], initiates (β = –0.97; 95% CI = –1.36, –0.57) and persistent users (β = –1.26; 95% CI = –1.81, –0.72). Conclusion This new prospective study builds from anecdotes, pre-clinical studies and cross-sectional evidence on inverse associations linking cannabis use and obesity and shows an inverse cannabis–BMI increase association. Confirmatory studies with rigorous cannabis and BMI assays will be needed.