Background: Hexahydrocannabinol (HHC) is a semi-synthetic cannabinoid which was marketed and sold openly in Ireland as a legal alternative to cannabis products until it was controlled in July 2025. There have been reports of psychotic illness precipitated by HHC use. Consequently, there are fears that HHC may become a public health issue. This study’s aim was to measure the extent of HHC use and patterns of use among adults in Ireland who use drugs.

Methods: Data on HHC use in Ireland were collected from participants aged 18+ years (N = 2314) who had used drugs in the previous year via the 2024 European Web Survey on Drugs, which included questions on frequency of use; reasons for starting and using; how HHC was obtained and administration method; and harms arising from use.

Results: In total, 36.2 % reported lifetime HHC use, 33.5 % last-year use, and 17.8 % last-month use. The primary motive for first using HHC was its easy availability in stores and the main source of HHC reported was a high street shop (62.4 %). Negative consequences arising from HHC use were reported by 89.9 % of respondents: 14.7 % reported anxiety or panic reactions, while 13.4 % felt faint or dizzy and 11.9 % reported dissociation or depersonalisation. Hallucinations or psychosis were reported by 3.9 %, depression by 3.6 %, and withdrawal symptoms by 3.2 %.

Conclusions: These data suggest that HHC has become a prominent feature of the Irish drug landscape. Given its harm potential, it will be important to monitor HHC use and related health harms.