Among patients referred to an early psychosis service, medicinal cannabis prescriptions after psychosis onset had higher mean THC concentrations (31.4% vs 16.9%) than pre-psychosis prescriptions, with over 60% experiencing further mental health deterioration attributed to the medication.
Psychiatrists, medicinal cannabis prescribers, and policymakers overseeing cannabis prescription safety.
THC concentration: 16.9% pre-psychosis vs 31.4% post-psychosis
What the researchers found
Before referral, 3.2% of patients were prescribed medicinal cannabis; after psychosis, this rose to 6.8%. Mean THC concentrations in prescriptions were nearly double after psychosis onset (31.4% vs 16.9%). Over 70% of those prescribed stimulants and 60% prescribed medicinal cannabis after a psychotic episode had further mental health service contact where these medications were thought to contribute to deterioration.
Why it matters
This raises serious safety concerns about medicinal cannabis prescribing practices for patients with psychosis history. Higher THC concentrations after psychosis onset goes against established evidence that THC can worsen psychotic symptoms.
The numbers in context
N = 220 referrals. Pre-psychosis: 3.2% prescribed medicinal cannabis, mean THC 16.9%. Post-psychosis: 6.8% prescribed, mean THC 31.4%. 60% of post-psychosis medicinal cannabis patients had further mental health contact attributed to medication.
How the study worked
Retrospective review of 220 consecutive early psychosis referrals (2019-2023) in Queensland, Australia. Clinical records were reviewed for stimulant and medicinal cannabis prescriptions before and after referral, with THC concentration data extracted from prescriptions.
What this study cannot tell us
Small numbers of medicinal cannabis patients (7 pre, 15 post). Retrospective design cannot prove causation between prescriptions and deterioration. Attribution of deterioration to medication may be subjective. Single service in one Australian state.
How to read the evidence
Small retrospective review raising important safety signals but with limited numbers and potential attribution bias.
When this study was published
Published in 2025 with data from 2019-2023.
The bigger picture
Australia's medicinal cannabis market has grown rapidly, and prescribing outside of specialist psychiatric oversight appears to be occurring without adequate consideration of psychosis risk. This study highlights a potential gap in prescriber education and patient safety systems.
Questions still open
- Are prescribers of medicinal cannabis adequately screening for psychosis history? Should medicinal cannabis registries flag patients with psychotic disorder diagnoses?
Common questions
Is medicinal cannabis safe for people with psychosis?
Why did THC concentrations increase after psychosis?
Read the original research
Stimulant and medicinal cannabis prescribing in patients referred to an early psychosis service in Queensland: A brief report.
Australasian psychiatry : bulletin of Royal Australian and New Zealand College of Psychiatrists, 10398562251406048
Citation
McArdle, Peter; Trott, Mike; Warren, Nicola; De Silva, Dilprasan; Smith, Lesley; Ritchie, Sarah; Siskind, Dan. (2025). Stimulant and medicinal cannabis prescribing in patients referred to an early psychosis service in Queensland: A brief report.. Australasian psychiatry : bulletin of Royal Australian and New Zealand College of Psychiatrists, 10398562251406048. https://doi.org/10.1177/10398562251406048
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