Alcohol and cannabis: Unraveling their impact on mental health

This study aimed to understand the interplay between alcohol use, cannabis use and mental health across the lifespan by addressing the following questions: (1) Do the structure and overall connectivity of mental health symptom networks differ between individuals who use alcohol and those who co-use alcohol and cannabis?; (2) Within co-users, what is the strength of the associations between characteristics of alcohol and cannabis use (quantity/frequency, severity of use-related problems and age of onset) and mental health symptoms?; and (3) Does age moderate these associations among co-users? Cross-sectional observational study including 740 participants aged 16-81 years, of which 446 used alcohol (57.6% female) and 294 co-used alcohol and cannabis (50.7% female). Data were collected online from English- and Dutch-speaking participants across multiple countries. Main outcome measures included self-reported severity of mental health symptoms (DSM-Level 1-Cross-Cutting Symptom Measure), quantity/frequency and problematic use of cannabis (Cannabis Use Disorder Identification Test - Revised) and alcohol (Alcohol Use Disorder Identification Test). Using a network approach, interactions between mental health symptoms (12 nodes) were compared between alcohol users and alcohol and cannabis co-users. In co-users, we incorporated detailed measures of alcohol and cannabis use (6 nodes) in the network and assessed the moderating role of age. The alcohol and cannabis co-use group was characterized by higher quantity/frequency of use, problematic use and severity for all mental health symptoms compared with the alcohol group (Ps ≤ 0.001). Still, the alcohol use and alcohol-cannabis co-use networks did not statistically significantly differ (network invariance test: maximum difference in edge weights = 0.167, P = 0.611, global strength invariance test: global strength difference statistic = 0.265, P = 0.470), with both showing strong connections between anxiety, personality functioning and depression. However, the centrality invariance test revealed a statistically significantly (P = 0.018) higher strength of somatic symptoms in co-use (strength = 1.31) compared with alcohol use (strength = 0.17). When substance use outcomes were included in the co-use network, distinct associations emerged: alcohol-related problems were uniquely linked to anxiety, impaired personality functioning and suicidal ideation (partial cor. = 0.03, 0.01 and 0.01, respectively), while cannabis-related problems were associated with mania and dissociation (partial cor. = 0.05 and 0.02). Age did not moderate these relationships. Alcohol use and alcohol-cannabis co-use appear to be associated with a range of mental health symptoms, including overlapping and distinct symptom patterns that are similar regardless of age.