New Monash University research has found that more than half of all adverse events reported to Australia's medicines regulator involving medicinal cannabis were linked to higher-THC products, with psychiatric disorders the most commonly reported adverse reactions.
Australia has seen a significant shift in medicinal cannabis prescribing in recent years, from products with lower THC concentrations to higher-THC products. More than 1,000 unregistered medicinal cannabis products are now available for prescription in Australia, none of which have been assessed by the Therapeutic Goods Administration (TGA) for efficacy, safety or quality.
The study, published in the Australian and New Zealand Journal of Psychiatry, examined 1,124 adverse events from 614 reports made to the TGA involving medicinal cannabis between mid-2022 and May 2025.
Researchers found that Category 5 products, which can contain THC concentrations ranging from 13 per cent to more than 88 per cent, accounted for more than half of all adverse event reports (54.1 per cent). Dried flower was the most common product form involved, followed by oral liquids and e-cigarette products.
Psychiatric disorders were the leading category of adverse events reported overall (30.6 per cent) and for higher-THC products specifically (31.9 per cent). The most frequently reported psychiatric adverse reactions for higher-THC products were anxiety, psychotic disorder and paranoia. Fourteen cases involved suicidal ideation, suicidal behaviour or suicide attempt.
Respiratory disorders were the fourth most commonly reported adverse event category.
The findings reflect a shift from an earlier analysis of TGA adverse event reports up to early 2023, when nervous system disorders were the leading category and most cases involved combination CBD and THC products.
Lead author Myfanwy Graham, an NHMRC Postgraduate Scholar and Monash Research Excellence Scholar, said the findings highlight the need for better screening and monitoring of patients prescribed higher-THC medicinal cannabis.
"In our earlier analysis, most reports involved combination CBD and THC products. In this study, higher-THC products account for more than half of all reports and psychiatric disorders, including anxiety, psychotic disorder and paranoia, are the leading adverse reactions. We also saw reports of suicidal ideation and behaviour," Ms Graham said.
"These findings suggest that vulnerable people are not being effectively screened and managed in clinical practice."
Ms Graham said the true number of adverse reactions is likely much greater than the data suggests, given the well-known limitations of voluntary adverse event reporting systems.
"These reports capture only a fraction of the adverse events that actually occur. The fact that we are seeing this volume of psychiatric adverse reactions even with significant under-reporting should prompt a closer look at how these products are being prescribed and monitored," Ms Graham said.
Read the research paper: https://staging.journals.sagepub.com/doi/10.1177/00048674261445267
