Towards quantifying the reciprocal associations between frequency of cannabis use and alcohol consumption: a cross-lagged analysis from the CONSTANCES cohort

OBJECTIVE: Disentangle the temporal relationships between frequency of cannabis use and alcohol consumption. METHODS: A cross-lagged model providing standardised coefficients (SCs)±their standard errors in 13 255 men and 13 696 women enrolled in 2015 or 2016 in the French population-based 'CONSulTANts des Centres d'Examens de Santé' (CONSTANCES) cohort. Cannabis use was categorised as follows: ‘No use during the past 12 months’, ‘Use during the past 12 months but not in the past month’ and ‘Use in the past month’ for cannabis use at baseline, and No use during the past 12 months, ‘Use less than once per month’ and ‘Use once per month or more’ for cannabis use at 1 year of follow-up. Alcohol consumption was measured at baseline and at 1 year of follow-up and three categories were determined: low risk (<28 drinks per week in men; <14 drinks per week in women), moderate risk (≥28 and<42 in men; ≥14 and<28 in women) and high risk (≥42 in men; ≥28 in women). Analyses were adjusted for age, sex, education, income, tobacco consumption, self-rated health status and depressive symptoms. RESULTS: Both associations from alcohol to cannabis and from cannabis to alcohol were significant (SC=0.02±0.01 with p=0.003 and SC=0.06±0.01 with p<0.001, respectively). However, the SC of the association from cannabis to alcohol was three times higher than the opposite association (p<0.001). After stratification for sex, SCs of the association from cannabis to alcohol were more than two times higher than for the opposite association in men, and more than four times higher in women (both p<0.001). CONCLUSIONS: The association between frequency of cannabis use and subsequent alcohol consumption was stronger than the opposite association. This finding encourages considering the risk of increased alcohol consumption among cannabis users.