A decade of cannabis-related hospital admissions in Victoria, Australia: A retrospective observational study

Background and aims Over the past decade, there has been increased lifetime use of illicit and medical cannabis, underscoring the need to examine public health impacts. This included reports of increased cannabis-related psychosis. In this context, this study aimed to determine all cannabis-related hospital admissions over a ten-year period to characterise poisonings and mental health harms. Design This is a retrospective observational study of the Victorian Admitted Episodes Dataset (VAED) records, which include all hospital admissions in the state of Victoria and are supplied by the Victorian Department of Health. Setting Victoria, Australia. Cases Hospital records for poisoning (T40.7) and mental health and behavioural disorders (F12.0-F12.9) related to use of cannabis for the period July 2013 to June 2023 were selected for this study. Measurements Crude and age-standardised rates per 100,000 population are reported. Net percentage change over the ten-year study window was estimated using generalised linear models with a log-population offset, contrasting the final year (2022/23) against the baseline (2013/14). Findings There were 39,565 cannabis-related admissions in the ten-year period, including 7263 admissions where cannabis-related harm was the principal diagnosis. The age-standardised rate per 100,000 population was 63.6 for all cannabis-related harm admissions and 11.7 for principal diagnosis cases. The peak annual rate for all cannabis-related harm was observed in 2020/2021 (77.3 per 100,000). There was a 49.0% (p<0.0001) increase in the rate of hospital admissions with a cannabis-related principal diagnosis, when comparing 2022/23 with baseline (2013/14). Overall, harmful use (F12.1) was the most common cannabis-related mental and behavioural disorder. Psychotic disorder (F12.5) was the most common diagnosis (45.3%; n=2,909/6,421). When considering principal diagnosis only, the rates were highest in males aged 15-24 years (36.9/100,000), followed by females in the same age group (20.5/100,000). While most principal diagnosis cases involved males, a greater percentage change between the first and last years of the study period was observed for females (+75.1%, p<0.0001) compared with males (+34.6%, p=0.003). Conclusions A 49% increase in the rate of cannabis-related hospital admissions, particularly mental and behavioural disorders due to use of cannabinoids, has occurred over the past decade. These trends are non-linear, rates in the last two years were lower than the peak in 2020/2021.