Medicinal Cannabis THC Concentrations Were Higher After Psychosis Than Before in Australian Patients
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?Are prescribers of medicinal cannabis adequately screening for psychosis history?
- ?Should medicinal cannabis registries flag patients with psychotic disorder diagnoses?
Trust & Context
- Key Stat:
- THC concentration: 16.9% pre-psychosis vs 31.4% post-psychosis
- Evidence Grade:
- Small retrospective review raising important safety signals but with limited numbers and potential attribution bias.
- Study Age:
- Published in 2025 with data from 2019-2023.
- Original Title:
- Stimulant and medicinal cannabis prescribing in patients referred to an early psychosis service in Queensland: A brief report.
- Published In:
- Australasian psychiatry : bulletin of Royal Australian and New Zealand College of Psychiatrists, 10398562251406048 (2025)
- Authors:
- McArdle, Peter, Trott, Mike, Warren, Nicola, De Silva, Dilprasan, Smith, Lesley, Ritchie, Sarah, Siskind, Dan
- Database ID:
- RTHC-07092
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Is medicinal cannabis safe for people with psychosis?
This study raises concerns. Patients prescribed higher-THC medicinal cannabis after psychosis experienced further deterioration. THC is known to worsen psychotic symptoms, and this data suggests prescribing practices may not adequately account for this risk.
Why did THC concentrations increase after psychosis?
The study did not determine why. Possible explanations include different prescribers with less awareness of psychiatric history, patient requests for stronger products, or prescriptions for non-psychiatric conditions without coordinating with mental health providers.
Read More on RethinkTHC
- THC-amygdala-anxiety-brain
- anandamide-weed-withdrawal
- cannabinoid-receptors-recovery-time
- cannabis-developing-brain-teenagers
- cant-enjoy-anything-without-weed
- dopamine-recovery-after-quitting-weed
- endocannabinoid-system-explained-simply
- endocannabinoid-system-withdrawal
- nervous-system-weed-withdrawal-fight-flight
- teen-weed-use-under-18-effects-brain
- thc-brain-withdrawal
- thc-prefrontal-cortex-brain-effects
- weed-cortisol-stress-hormones
- weed-memory-loss-recovery
- weed-motivation-amotivational-syndrome
- weed-nervous-system-effects
- weed-reward-system-brain
Cite This Study
https://rethinkthc.com/research/RTHC-07092APA
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
MLA
McArdle, Peter, et al. "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, 2025. https://doi.org/10.1177/10398562251406048
RethinkTHC
RethinkTHC Research Database. "Stimulant and medicinal cannabis prescribing in patients ref..." RTHC-07092. Retrieved from https://rethinkthc.com/research/mcardle-2025-stimulant-and-medicinal-cannabis
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.