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.