Cannabis use undermines psychosis treatment and worsens depression

Medication non-adherence and cannabis use represent significant challenges in treating first-episode psychosis (FEP). This study examines interrelationships among medication adherence, cannabis use, and depressive symptoms in FEP patients over nine months. Sixty-six participants with FEP (aged 18-45) without severe comorbid substance use disorders (except cannabis) from psychiatric services in northern Italy were assessed at baseline, three months, and nine months using standardized measures including the Medication Adherence Rating Scale (MARS), Positive and Negative Syndrome Scale (PANSS), Calgary Depression Scale for Schizophrenia (CDSS), and Scale for Suicide Ideation (SSI). Cannabis use was assessed through self-reports and urine toxicology. Longitudinal trajectories were examined using mixed-effects models and cross-lagged panel analyses. Participants with lower MARS scores showed significantly higher depression scores. Cannabis use at baseline predicted lower adherence at three months (β = -0.31, p = 0.008), while baseline adherence predicted lower depression at three months (β = -0.24, p = 0.018). Cross-lagged analyses revealed bidirectional relationships between adherence and depression. Baseline predictors of poor adherence included baseline depression (OR = 1.89), cannabis use (OR = 2.15), and medication side effects (OR = 1.76). Bidirectional relationship exists between medication adherence and depressive symptoms in FEP, creating potential negative cycle. Early screening and integrated interventions addressing adherence and mood may improve outcomes.