Clinical characteristics of HHC-associated psychosis: an exploratory retrospective inpatient cohort study

To describe the demographic, clinical, and treatment characteristics of individuals admitted with hexahydrocannabinol (HHC)-associated psychosis and compare with cannabis-associated psychosis.

A retrospective chart review was undertaken of all admissions to the Adult Acute Mental Health Unit at University Hospital Galway, Ireland, between 1 May 2023 and 31 July 2025, with psychosis and documented HHC or cannabis use in the seven days preceding admission. Demographic, clinical, and treatment variables were compared across three groups: HHC-only, cannabis-only, and combined HHC + cannabis associated psychosis. Group differences were examined using ANOVA for continuous variables and Fisher's exact tests for categorical variables, with repeated-measures ANOVA used to examine antipsychotic dosing. Analyses were exploratory in nature.

Thirty-three individuals (79% male) met inclusion criteria. All HHC-related cases occurred in a first episode of psychosis. Affective symptoms were more frequent in the HHC-only group (89%) than in the cannabis-only (54%) and combined HHC + cannabis groups (27%) (p = 0.024). Formal thought disorder appeared more common in HHC-exposed groups (80%) compared with cannabis-only presentations (38%), reaching statistical significance in an exploratory comparison between cannabis-only and combined HHC-exposed groups (p = 0.027). Urine toxicology screening for THC metabolites, length of stay and maximum antipsychotic dose were similar across groups.

In this cohort, HHC-associated psychosis was associated with higher rates of affective symptoms and formal thought disorder than cannabis-related presentations, despite otherwise similar clinical features. Findings are hypothesis-generating, given the exploratory analyses, small sample and uncorrected multiple testing. They suggest a potential role for novel cannabinoid screening to support earlier identification and management.