Background: Motives to use cannabis play a central role in the development and maintenance of problematic cannabis use and previous studies stressed sex-related differences on motives to use cannabis. However, motives cannot be validly compared in men and women without first establishing the measurement invariance across sex. Therefore, the aim of the study is to (1) examine for the first time the measurement and structural invariance of the Marijuana Motives Measure (MMM) across sex, and (2) to investigate the motives for cannabis use that best explain problematic use.

Methods: 2951 (41.7% women) users of the "Stop cannabis" smartphone app of which 99.8% reported having used cannabis in the last three months completed an online MMM and ASSIST to assess the severity of their problematic cannabis use.

Results: Multigroup confirmatory factor analyses supported measurement invariance across sex, whereas structural invariance was not confirmed. Indeed, group comparisons indicated that women reported greater coping motives then men whereas men showed greater social motives than women. A multiple linear regression analysis showed that only coping and conformity motives were significantly associated with greater problematic cannabis use, whereas neither sex nor the sex by motives interactions were significantly related to problematic cannabis use.

Conclusions: The MMM appears to function comparably across men and women. Therefore, sex-related comparisons on the questionnaire can be considered valid. Coping and conformity motives may play a central role part in the development of marijuana use problems which may hold implications for intervention development and public policy.