A recent study led by researchers from Monash University has uncovered troubling patterns in adverse events associated with higher-strength medicinal cannabis products in Australia. Analyzing over 1,100 reports submitted to the Therapeutic Goods Administration (TGA), the team found that products with elevated levels of tetrahydrocannabinol (THC)—the primary psychoactive compound in cannabis—were linked to a disproportionate number of psychiatric side effects, including anxiety, psychotic disorders, and paranoia. This research, published in the Australian and New Zealand Journal of Psychiatry, highlights a shift in prescribing practices that warrants closer scrutiny by healthcare professionals and regulators alike.

The findings come at a time when medicinal cannabis prescriptions have surged across the country, with nearly one million approvals issued by the end of 2025. Universities like Monash and the University of Sydney are at the forefront of this investigation, providing evidence-based insights into both the potential benefits and risks of these treatments. As Australian institutions continue to lead global conversations on cannabinoid research, this work underscores the need for rigorous clinical trials and better prescriber education.

Understanding the Study's Methodology and Data

The Monash-led analysis examined voluntary adverse event reports to the TGA from mid-2022 to May 2025, covering 614 cases and 1,124 individual events. Researchers categorized products using TGA classifications, focusing on 'Category 5' items dominated by THC concentrations ranging from 13% to over 88%—far exceeding typical natural plant levels of up to 30-35%. Dried flower for inhalation was the most common form implicated, reflecting evolving access pathways.

Psychiatric disorders emerged as the leading category, accounting for 30.6% of all events and 31.9% specifically for high-THC products. Among these, anxiety topped the list with 54 reports, followed by psychotic disorder (18 cases) and paranoia (17 cases). Alarmingly, 14 cases involved suicidal ideation, behavior, or attempts. Respiratory issues, such as cough and shortness of breath, also rose with inhaled high-THC formats.

In contrast, products high in cannabidiol (CBD) or balanced CBD-THC blends primarily triggered gastrointestinal complaints like nausea and vomiting. This distinction points to THC as a key driver of mental health-related harms, a pattern not as pronounced in earlier data up to 2023 when nervous system disorders dominated.

The Rise of High-THC Products in Australian Prescribing

Since medicinal cannabis became accessible via the TGA's Special Access Scheme in 2016, prescriptions have exploded. By late 2025, sales peaked at 3.72 million units in the first half before a 28.5% dip amid regulatory tightening. Mental health conditions rank among top indications, alongside chronic pain, despite limited evidence for efficacy.

High-THC products now comprise over half of approvals, often unregistered and unassessed for quality or safety. Universities such as the University of Newcastle and University of Queensland contribute to the Australian Centre for Cannabinoid Clinical and Research Excellence (ACCaRE), advocating for standardized evidence. Yet, the Monash study reveals underreporting—voluntary systems capture only a fraction of incidents—suggesting real-world risks may be higher.

Psychiatric Risks: Anxiety, Psychosis, and Beyond

High-THC cannabis disrupts brain chemistry, particularly in the endocannabinoid system regulating mood and perception. The study's data aligns with global patterns where potent strains double psychosis risk in vulnerable youth. In Australia, first-time psychosis cases post-prescription have risen, prompting emergency interventions.

Anxiety, the most reported event, manifests as acute panic or chronic worry, often exacerbated by THC's biphasic effects—low doses may calm, but high ones provoke distress. Psychotic symptoms like hallucinations or delusions appeared in 18 high-THC cases, echoing warnings from the Royal Australian and New Zealand College of Psychiatrists (RANZCP). Suicidal ideation adds urgency, especially amid youth mental health crises.

Insights from the Landmark University of Sydney Lancet Review

Complementing the Monash analysis, a March 2026 Lancet Psychiatry review by University of Sydney's Matilda Centre—led by Dr. Jack Wilson—synthesized 54 randomized controlled trials spanning 1980-2025. It found no reliable evidence cannabinoids outperform placebo for anxiety, PTSD, depression, or psychosis symptoms.

• No effect on Positive and Negative Syndrome Scale (PANSS) for psychosis.
• Null results for PTSD Checklist scores.
• Increased adverse events overall (odds ratio 1.75), including nausea and fatigue.

Lead researcher Emily Stockings emphasized short trial durations (average 5 weeks) and low-THC doses fail to mirror real-world high-potency use. This uni-led work calls for pausing routine prescriptions pending robust trials.Read the full Lancet review.

Regulatory and Clinical Responses from Australian Authorities

The TGA, responding to mounting data, launched a 2026 review of unapproved products after 500+ submissions. Guidance advises against THC for those with psychosis history or anxiety disorders, favoring vaporizers over smoking to minimize toxins.

Universities play pivotal roles: Sydney's Lambert Initiative pioneers cannabinoid therapeutics, while Monash's Addiction Research Centre informs policy. Prescribers must screen via tools like the Cannabis Use Disorder Identification Test (CUDIT), yet the study suggests gaps persist.

Stakeholder Perspectives: Patients, Doctors, and Researchers

Myfanwy Graham, NHMRC scholar at Monash, noted, "Vulnerable populations aren't being screened effectively." Patients report mixed outcomes—some praise pain relief, but mental health seekers face worsening symptoms. Psychiatrists warn high-THC delays evidence-based therapies like CBT.

Advocates urge balanced CBD-THC ratios, echoing uni calls for Category 5 restrictions. Broader implications include training for 50,000+ prescribers via uni-led programs.

Australian Universities Leading Cannabis Research

Beyond these studies, institutions drive innovation: UQ's National Centre for Youth Substance Use Research examines youth risks; Newcastle's ACCaRE builds clinical frameworks. Lambert (Sydney) unlocks therapeutic potentials, funding trials via NHMRC.

Challenges persist—funding lags, ethics hurdles—but unis position Australia as a hub. Future grants target long-term safety, pharmacovigilance.Explore Sydney's Lambert Initiative.

Implications for Higher Education and Public Health

These findings ripple through health sciences curricula, prompting unis to integrate cannabis pharmacodynamics. Research jobs surge in pharmacology, epidemiology—opportunities for postdocs, lecturers.TGA medicinal cannabis hub.

Public health: Screen young patients rigorously; prioritize low-THC. Economic costs of psychosis hospitalizations (millions annually) underscore prevention.

Photo by Elsa Olofsson on Unsplash

Future Outlook: Calls for Rigorous University-Led Trials

Experts advocate Phase III trials mirroring real-world use, uni collaborations with TGA. Potential: Optimized formulations minimizing risks. Until then, evidence tempers enthusiasm—unis lead the balanced path forward.