["Addiction, Volume 121, Issue 6, Page 1421-1433, June 2026. ", "\nAbstract\n\nAims\nThis 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?\n\n\nDesign, setting and participants\nCross‐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.\n\n\nMeasurements\nMain 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.\n\n\nFindings\nThe 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.\n\n\nConclusions\nAlcohol 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.\n\n"]