Medicinal Cannabis an Mental Health Hospitalisation: An Observational Study

Background The prescription of medicinal cannabis (MC) in Australia has increased 15-fold since 2019. There is limited evidence regarding the most suitable doses of individual cannabis products, including Δ9-tetrahydrocannabinol (THC), which is problematic for people who are vulnerable to psychosis. There is paucity of data on the impact of this increase on psychiatric outcomes for people prescribed medicinal cannabis in Australia. Aims & Objectives To determine the rate of MC prescription on admission, the strength of prescribed cannabis products, and psychiatric outcomes of patients admitted to an inpatient psychiatric unit Method We conducted a retrospective audit of 750 patients admitted to an adult inpatient psychiatric unit between 2021 and 2023 Results 4.7% of all admissions to the inpatient unit during the study period were prescribed MC in the 90 days prior to admission, with an increasing trend over time. Of those prescribed medicinal cannabis, over 50% had pre-existing severe mental illness. 70% of prescriptions contained THC, and 77% contained less than 2% cannabidiol (CBD). The most common indication reported was anxiety, in 46% of patients. 91% of patients prescribed medicinal cannabis were admitted with psychosis symptoms. 23% had first episode psychosis, and 69% presented with a relapse of a psychotic disorder. Discussion & Conclusions This study is the first to present the rates of medicinal cannabis prescription upon admission to a metropolitan psychiatric inpatient unit since the legalisation of medicinal cannabis in 2016. The substantial rise in medicinal cannabis prescription, particularly those containing high levels of THC and low levels of CBD, appears to have significant implications for psychiatric outcomes among vulnerable populations.