Cannabis has been shown to be linked to the development of psychotic illness. Although it has been legalised in many jurisdictions over the last 20 years, its apparent detrimental effects on mental health has slowed its legalisation on a widespread basis in Europe. However, a possible consequence of continuing illegality is that users in an unregulated environment are consuming high-potency or synthetic cannabinoids, which may also lead to adverse effects, including psychosis.1

In Ireland, the Criminal Justice (Psychoactive Substances) Act 2010 prohibited the sale of any psychoactive substance, including synthetic cannabinoids, with the capacity to ‘produce stimulation or depression of the central nervous system of the person, resulting in hallucinations or a significant disturbance in, or significant change to, motor function, thinking, behaviour, perception, awareness or mood’ (p. 4).2 However, hexahydrocannabinol (HHC) is classified as semi-synthetic, rather than synthetic, because it is synthesised from cannabidiol, which in turn is often derived from low-tetrahydrocannabinol (THC) cannabis (hemp). Consequently, HHC is marketed openly as a ‘legal’ alternative to cannabis products and has been produced and marketed in various forms, including being sprayed onto low-THC cannabis flower and resin. Although it has been hypothesised that semi-synthetic cannabinoids such as HHC may lead to psychotic illness, no such relationship has yet been reported in the scientific literature.

In a 2024 article published in the Irish Journal of Psychological Medicine, O’Mahony et al. describe two cases of psychotic illness which appear to have been precipitated by use of legally purchased HHC.3 In both cases, the patients were regular cannabis users, but the episodes of psychotic illness only developed when they began vaping HHC. Both were diagnosed with synthetic cannabinoid-induced psychotic disorder (International Classification of Diseases, Eleventh Revision (ICD-11) code 6C42.6). As with cannabis-induced psychosis, the presentations were heterogeneous in phenomenology. One patient presented with delusions of guilt and persecution, as well as auditory hallucinations. The other patient presented with prominent thought disorder, notably alogia, as well as disordered subjective time.

The authors note that, as of March 2023, HHC use has been reported in 70% of European Union member states, which likely represents an underestimate. Given the widespread and increasing use of vaping and the ready access to this compound, they suggest that clinicians and policy-makers should be aware of HHC’s psychotogenic potential in order to protect potentially vulnerable patients from deleterious effects through psychoeducation and legislative restriction.

1    Murray RM, Quigley H, Quattrone D, Englund A and Di Forti M (2016) Traditional marijuana, high-potency cannabis and synthetic cannabinoids: increasing risk for psychosis. World Psychiatry, 15(3): 195–204.

2    Department of Justice and Law Reform (2010) Criminal Justice (Psychoactive Substances) Act 2010. Available from: https://www.oireachtas.ie/en/bills/bill/2010/34/

3    O’Mahony B, O’Malley A, Kerrigan O and McDonald C (2024) HHC-induced psychosis: a case series of psychotic illness triggered by a widely available semisynthetic cannabinoid. Ir J Psychol Med, 14: 1–4. Available from:
https://www.drugsandalcohol.ie/40495/