A series of recent studies and analyses have concluded that there is insufficient high-quality evidence to support the routine use of medicinal cannabis for treating most mental health disorders.
Research published in The Lancet Psychiatry and the Australian and New Zealand Journal of Psychiatry indicates that while some patients report subjective benefits, the overall data does not demonstrate clinical effectiveness for conditions like anxiety, depression, and PTSD, and points to increased risks associated with high-THC products.
Combined Analysis of Multiple Studies
Review by the University of Sydney and International Partners
A comprehensive meta-analysis, led by researchers from the University of Sydney, the University of Queensland, Monash University, and institutions in England, examined 54 randomized controlled trials conducted between 1980 and May 2025, involving 2,477 participants. The review assessed cannabinoids as a primary treatment for mental health and substance-use disorders.
Key Findings:
- No significant benefit was found for the treatment of anxiety disorders, psychotic disorders, post-traumatic stress disorder (PTSD), or opioid-use disorder.
- No randomized controlled trials evaluating cannabinoids for depression were identified.
- Limited evidence suggested potential benefits for specific conditions, including:
- Reduction of cannabis withdrawal symptoms and lower cannabis consumption for cannabis-use disorder (with a CBD/THC combination).
- Reduction in tic severity for Tourette’s syndrome.
- Reduction in some autistic traits for autism spectrum disorder.
- Increased sleep time for patients with insomnia.
"The routine use of cannabinoids for the treatment of mental disorders and substance use disorders is currently rarely justified."
However, the overall quality of evidence for autism and insomnia was deemed low. The study concluded that the routine use of cannabinoids for these conditions is rarely justified.
Monash University Study on Adverse Events
A separate study by Monash University analyzed 1,124 adverse events from 614 reports made to Australia's Therapeutic Goods Administration (TGA) between mid-2022 and May 2025.
Key Findings:
- Category 5 products (containing 13% to over 88% THC) accounted for 54.1% of all adverse event reports.
- The most common product forms involved were dried flower, followed by oral liquids and e-cigarette products.
- Psychiatric disorders were the leading category of adverse events overall (30.6%) and for higher-THC products (31.9%).
- The most frequently reported psychiatric adverse reactions for higher-THC products were anxiety, psychotic disorder, and paranoia.
- Fourteen reports involved suicidal ideation, suicidal behavior, or suicide attempt.
"Vulnerable people are not being effectively screened and managed in clinical practice." — Myfanwy Graham, Monash University
An earlier analysis of TGA reports up to early 2023 had found nervous system disorders as the leading category, with most cases involving combination CBD and THC products.
Context and Regulatory Landscape
Prescribing Patterns vs. Research
In Australia, medicinal cannabis was legalized in 2016 and prescription regulations were expanded in 2021 to cover over 250 health conditions. Evidence from medical cannabis clinics indicates that mental illnesses like anxiety and depression are frequently cited by patients as primary reasons for seeking treatment.
For anxiety, products with the highest THC levels receive nearly three times more approvals than those containing only CBD, a trend that does not align with current research where most high-quality clinical trials for anxiety have focused on CBD-based products, not THC.
Expert and Industry Responses
- Lead author Jack Wilson (University of Sydney) stated that while some individuals may report benefits, the overall evidence does not support the routine use of these medicines, and noted that the risk of developing a cannabis-use disorder among medical users is comparable to non-medical users.
- Myfanwy Graham (Monash University) stated that the findings indicate vulnerable people are not being effectively screened and managed in clinical practice.
- Dr. McMullen (President of the Australian Medical Association) stated that the study highlights the necessity for more robust regulatory oversight. He acknowledged that medicinal cannabis can be beneficial for patients with specific, evidence-backed conditions such as epilepsy, chemotherapy-induced nausea, or muscle spasticity associated with Multiple Sclerosis.
- Cannabis Council Australia stated that the review's findings do not signify an end for the industry, emphasizing the need for a comprehensive real-world evidence data registry to formally evaluate safety, quality, and efficacy.
- Drug safety group Penington stated that while many patients report benefits, insufficient data exists for definitive conclusions, advocating for cautious reforms to regulations.
Safety and Risks
Increased Potency and Associated Risks
The amount of THC in marijuana has increased significantly over time. Lead author Jack Wilson noted that the use of medicinal cannabis can also make mental health symptoms worse. The TGA advises against THC-containing products for those with a personal or family history of psychosis or schizophrenia, and cautions use in people with current or past mood or anxiety disorders.
Potential Risks for Vulnerable Populations
- Brain Development: Use during pregnancy, adolescence, and young adulthood can interfere with brain development.
- Mental Health Disorders: Heavy use by teens and young adults with mood disorders is linked to an increased risk of self-harm, suicide attempts, and death.
- Psychotic Disorders: For individuals at high risk of bipolar or psychotic disorders (e.g., those with family histories), marijuana use may increase the risk of developing such conditions. Daily or near-daily cannabis use is linked to a higher risk of psychosis or may contribute to its development.
- Withdrawal Effects: Some individuals may interpret increased mental health symptoms upon discontinuing medicinal cannabis as evidence of its prior efficacy, but these symptoms may be due to cannabis withdrawal. Approximately one in three or four medicinal cannabis users may develop cannabis dependence and experience withdrawal symptoms if use is stopped suddenly.
Proven Alternatives for Mental Health
- Pharmaceutical Approach: Selective serotonin reuptake inhibitors (SSRIs) are commonly used for depression and anxiety.
- Psychotherapy: Cognitive behavioral therapy (CBT) is a leading psychotherapy for these conditions, often combined with SSRIs.
Conclusions
The recent research collectively indicates that the benefits of cannabis as a medicine may have been overstated for many mental health conditions. While potential benefits exist for certain specific conditions (cannabis-use disorder, Tourette's syndrome, autism, and insomnia), the quality of evidence is often low.
"The overall evidence does not support the routine use of these medicines for these conditions." — Jack Wilson, University of Sydney
Researchers and medical bodies emphasize the need for more high-quality trials with larger and more representative samples to clarify the therapeutic role of cannabinoids, as well as more robust regulatory oversight and prescribing safeguards.