Clinical characteristics of HHC-associated psychosis: an exploratory retrospective inpatient cohort study
Sarah Lanigan, Níall Lally, Aoife Brett, Brian William O’Mahony, Colm McDonald, Brian P. Hallahan
Irish Journal of Psychological Medicine October 19, 2026 DOI: 10.1017/ipm.2026.10240 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Retrospective chart review Peer reviewed |
|---|---|
| Sample size | 33 |
| Population | Individuals admitted 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 before admission |
| Key findings | HHC-associated psychosis was associated with higher rates of affective symptoms (89% in the HHC-only group vs 54% cannabis-only and 27% combined) and formal thought disorder (80% in HHC-exposed groups vs 38% cannabis-only) than cannabis-related presentations, despite otherwise similar clinical features. The authors describe the findings as hypothesis-generating given exploratory analyses, a small sample, and uncorrected multiple testing. |
Abstract
Objectives: To describe the demographic, clinical, and treatment characteristics of individuals admitted with hexahydrocannabinol (HHC)-associated psychosis and compare with cannabis-associated psychosis.
Methods: 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.
Results: 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.
Conclusion: 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.
Citations in the library
Cites 4
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- HHC-induced psychosis in adolescents: a case series Irish Journal of Psychological Medicine June 19, 2026
- Hexahydrocannabinol Pharmacology, Toxicology, and Analysis: The First Evidence for a Recent New Psychoactive Substance. Current Neuropharmacology 2023
- The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study The Lancet Psychiatry May 1, 2019