Huge study finds no evidence cannabis helps anxiety, depression, or PTSD

· ScienceDaily
Source:University of Sydney
Summary:The largest review of medicinal cannabis to date found it doesn’t effectively treat anxiety, depression, or PTSD—despite millions using it for those reasons. Researchers warn it could even make mental health worse, raising risks like psychosis and addiction while delaying proven treatments. Some limited benefits were seen for conditions like insomnia and autism, but the evidence is weak. The findings are fueling calls for stricter oversight as cannabis use continues to rise.
A sweeping new analysis finds medicinal cannabis doesn’t work for anxiety, depression, or PTSD—and may even make mental health worse. Credit: Shutterstock

A major paper published in The Lancet reports that medicinal cannabis does not effectively treat anxiety, depression, or post-traumatic stress disorder (PTSD). The analysis is the largest to date examining both the safety and effectiveness of cannabinoids across a wide range of mental health conditions.

These findings arrive at a time when cannabis use for medical purposes is widespread. About 27 percent of people aged 16-65 in the United States and Canada report using cannabis medically, and roughly half of them say they use it to manage mental health symptoms.

Lead author Dr. Jack Wilson from the University of Sydney's Matilda Centre said the results raise serious questions about approving medicinal cannabis for conditions like anxiety, depression, and PTSD.

"Though our paper didn't specifically look at this, the routine use of medicinal cannabis could be doing more harm than good by worsening mental health outcomes, for example a greater risk of psychotic symptoms and developing cannabis use disorder, and delaying the use of more effective treatments," he said.

Limited Evidence for Other Conditions

The researchers did find some indications that medicinal cannabis might help in certain cases. These include cannabis use disorder (otherwise known as cannabis dependency), autism, insomnia, and tics or Tourette's syndrome.

However, Dr. Wilson emphasized that the supporting evidence for these uses is not strong.

"But the overall quality of evidence for these other conditions, such as autism and insomnia, was low. In the absence of robust medical or counseling support, the use of medicinal cannabis in these cases are rarely justified.

"There is, however, evidence that medicinal cannabis may be beneficial in certain health conditions, such as reducing seizures associated with some forms of epilepsy, spasticity among those with multiple sclerosis, and managing certain types of pain, but our study shows the evidence for mental health disorders falls short.

"In the case of autism specifically, while the study showed some evidence medicinal cannabis could assist with a reduction in symptoms, it is worth noting that there is no one — or universal — experience of autism, so this finding should be treated with caution."

Mixed Results for Substance Use Disorders

The review also looked at how medicinal cannabis affects different substance use disorders. Results varied depending on the condition.

Cannabis-based treatments showed some potential for helping people with cannabis dependence. However, the study found a concerning effect in people with cocaine-use disorder, where cannabis use increased cravings.

"Similar to how methadone is used to treat opioid-use disorder, cannabis medicines may form part of an effective treatment for those with a cannabis-use disorder. When administered alongside psychological therapy, an oral formulation of cannabis was shown to reduce cannabis smoking," Dr. Wilson said.

"However, when medicinal cannabis was used to treat people with cocaine-use disorder, it increased their cravings. This means it should not be considered for this purpose and may, in fact, worsen cocaine dependence," he said.

Calls for Stronger Regulation of Medicinal Cannabis

The rapid rise in medicinal cannabis use and prescribing has raised concerns among major medical organizations, including the American Medical Association. Experts point to limited regulation and ongoing uncertainty about how effective and safe these products really are.

"Our study provides a comprehensive and independent assessment of the benefits and risks of cannabis medicines, which may support clinicians to make evidence-based decisions, helping to ensure patients receive effective treatments while minimising harm from ineffective or unsafe cannabis products," Dr. Wilson said.

Large Global Analysis Spanning 45 Years

The findings are based on a systematic review and meta-analysis of 54 randomized controlled trials (RCTs) conducted worldwide over a 45 year period (1980-2025).

The research was funded by the NHMRC. Wayne Hall and Myfanwy Graham have received consultation fees from the World Health Organization. Wayne Hall has received payment for expert testimony on the risks of cannabis use. Myfanwy Graham is an appropriate member of the Medicinal Cannabis Expert Working Group, Australian Department of Health, Ageing and Disability. Myfanwy Graham has also received funding from the Therapeutic Goods Administration for independent evidence reviews on medicinal cannabis. All other authors declare no competing interests.

Related Terms

Mental illnessMental disorder or mental illness are terms used to refer psychological pattern that occurs in an individual and is usually associated with distress or disability that is not expected as part of normal development or culture. The recognition and understanding of mental disorders has changed over time. Categories of diagnoses may include mood disorders, anxiety disorders, psychotic disorders, eating disorders, developmental disorders, personality disorders, and many other categories. In many cases there is no single accepted or consistent cause of mental disorders, although they are widely understood in terms of a diathesis-stress model and biopsychosocial model. Mental disorders have been found to be common, with over a third of people in most countries reporting sufficient criteria at some point in their life.Sleep disorderA sleep disorder (somnipathy) is a disorder in the sleep patterns of a person or animal. Sleep disorders include: Bruxism; delayed sleep phase syndrome; insomnia: jet lag or desynchronosis; narcolepsy; night terror; parasomnias; periodic limb movement disorder; rapid eye movement behavior disorder; restless legs syndrome;AnxietyAnxiety is a feeling of worry, nervousness, or unease that arises in response to stress or perceived threats. It is a normal and often helpful emotional response that can prepare the body to deal with challenges or danger. However, when anxiety becomes persistent, excessive, or disproportionate to the situation, it may interfere with daily functioning and be classified as an anxiety disorder.WorkaholicA workaholic is a person who is addicted to work. The term generally implies that the person enjoys their work; it can also imply that they simply feel compelled to do it. There is no generally accepted medical definition of such a condition, although some forms of stress, impulse control disorder, obsessive-compulsive personality disorder and obsessive-compulsive disorder can be work-related.NutritionNutrition is a science that examines the relationship between diet and health. Dietitians are health professionals who specialize in this area of study, and are trained to provide safe, evidence-based dietary advice and interventions.PsychopathologyPsychopathology is a term which refers to either the study of mental illness or mental distress or the manifestation of behaviours and experiences which may be indicative of mental illness or psychological impairment. The many different professions may be involved in studying mental illness or distress. Most notably, psychiatrists and clinical psychologists are particularly interested in this area and may either be involved in clinical treatment of mental illness, or research into the origin, development and manifestations of such states, or often, both. More widely, many different specialties may be involved in the study of psychopathology. For example, a neuroscientist may focus on brain changes related to mental illness. Therefore, someone who is referred to as a psychopathologist, may be one of any number of professions who have specialised in studying this area.