OBJECTIVE: Evidence suggests that psilocybin-assisted therapy (PAT) leads to durable shifts in personality structure. However, such changes have yet to be characterized in disorders of addiction. In this secondary analysis from a randomized controlled trial, the authors examined the effect of PAT on personality dimensions in patients with alcohol use disorder (AUD), hypothesizing that PAT would attenuate personality abnormalities in AUD and that reductions in trait impulsiveness would be associated with lower drinking. METHODS: Eighty-four adults with AUD were randomized to two medication sessions of either psilocybin (N=44) or active placebo (diphenhydramine; N=40), received 12 weekly psychotherapy sessions, and completed follow-up for an additional 24 weeks. Changes in personality traits (week 36 vs. baseline) were assessed with the revised NEO Personality Inventory; daily alcohol consumption was quantified using the timeline followback. RESULTS: Relative to the placebo group, the psilocybin group showed significant reductions in neuroticism and increases in extraversion and openness. Secondary analyses showed that reductions in neuroticism were driven by decreases in the facets depression, impulsiveness, and vulnerability; increases in openness were driven by increases in the facets openness toward feelings and fantasy. Across all participants, decreases in impulsiveness were associated with lower posttreatment alcohol consumption, and an exploratory analysis revealed that these associations were strongest among psilocybin-treated participants who continued moderate- or high-risk drinking prior to the first medication session. CONCLUSIONS: PAT elicited durable shifts in personality, suggesting normalization of abnormal personality trait expression in AUD. Further study is needed to clarify whether PAT exerts its beneficial effects by reducing impulsiveness or whether impulsive individuals inherently respond better to PAT.