Effects of a cannabis use disorder text message-delivered treatment on young adult alcohol misuse: Differential effects by gender.

Alcohol misuse is more prevalent, frequent, and severe among young adults who use cannabis. Treatment of dual alcohol and cannabis users may have mixed results, with some studies reporting that alcohol misuse increases when cannabis use decreases (substance substitution), while others report that alcohol misuse decreases along with decreasing cannabis use (treatment spillover), and others report no association. Additionally, little research tests whether gender differences are found in treatment of dual alcohol and cannabis users, which may be expected given previous alcohol-focused treatments showing larger effects for females. In the current study, we present a secondary analysis of a randomized clinical trial testing a text message-delivered cannabis use disorder (CUD) treatment (peer network counseling text or "PNC-txt"). The trial included 101 young adults ages 18-25 who met criteria for CUD. We tested whether alcohol use and binge drinking frequency (4+/5+ drinks for women/men) decreased in response to the PNC-txt treatment, which has previously shown effectiveness in reducing cannabis use days. Latent growth models tested PNC-txt effects on the monthly rate of change in alcohol use and binge drinking across three months. In the full sample, we found no evidence of significant treatment effects on alcohol use (d = -0.07) or binge drinking (d = -0.10). Moderation analyses, however, indicated the PNC-txt effect on both alcohol use and binge drinking differed significantly by gender. PNC-txt led to significantly larger decreases in alcohol use (d = -0.53) and binge drinking days (d = -0.43) across the three months for females, whereas the study saw opposite (but nonsignificant) effects for males (d = 0.30 and 0.16 for alcohol use and binge drinking, respectively). We found no evidence that reductions in alcohol use and binge drinking were associated with cannabis use decreases, arguing against direct substitution or spillover effects. These results provide evidence that treatments focused on cannabis use may have secondary beneficial effects for young-adult alcohol misuse, although such effects may be limited to women.