A recent study published in the journal BJPsych Bulletin sheds light on the growing concern over hexahydrocannabinol (HHC) and its apparent role in precipitating psychotic episodes.1 Conducted by a team of Irish psychiatrists and researchers from the University of Galway and Trinity College Dublin, the research explores the prevalence of HHC use among psychiatric admissions at University Hospital Galway and raises significant public health and legislative concerns.

HHC, a derivative of cannabidiol (CBD), has gained popularity in Ireland in recent years as an alternative to delta-9-tetrahydrocannabinol, the primary psychoactive component of cannabis. Out of a total of 214 cases admitted over a 21-month period (May 2023 to December 2024), the study identified 28 admissions (13.1%) for psychosis that were preceded by HHC use, and found that HHC was the second most common drug involved in psychosis presentations. Alarmingly, more than one-third of patients admitted for a first episode of psychosis had used HHC prior to admission. The median age of HHC users in the study was 24 years, which was significantly younger than non-users.

Unlike fully synthetic cannabinoids, HHC is labelled as ‘semi-synthetic’ because it is chemically derived from plant-based CBD. Critics argue that this label obscures its potent psychoactive potential, which is increasingly evident in both anecdotal and clinical reports. While some users describe HHC’s effects as mild or euphoric, the study’s findings suggest a strong correlation with the onset or exacerbation of psychotic symptoms, particularly among young males.

On 29 July 2025, the Minister for Health, Jennifer Carroll MacNeill; the Minister for Public Health, Wellbeing and the National Drugs Strategy, Jennifer Murnane O’Connor; and the Minister for Mental Health, Mary Butler, announced that the import, export, production, possession, sale, and supply of products containing HHC is now illegal in Ireland. However, the study authors call for urgent policy reform, emphasising that legislative and clinical systems must respond more swiftly to emerging psychoactive substances.

In conclusion, this research provides compelling evidence that HHC is not the benign cannabis substitute it is often marketed as, and that it poses real risks to mental health, particularly among young people. The findings underscore the importance of equipping clinicians and the public with accurate information about the dangers of novel cannabinoids.

1    O’Mahony B, Lanigan S, Lally N, et al. (2025) Novel substance, same old problems: admissions of psychosis precipitated by hexahydrocannabinol, a widely available semi-synthetic cannabinoid. BJPsych Bulletin: 1–6. Available from: https://www.drugsandalcohol.ie/43779/