Medical cannabis not effective as a mental health treatment, finds meta analysis

Routine use of medical cannabis for the treatment of mental health disorders is “rarely justified” based on current evidence, according to results of a review and meta-analysis.

Publishing their findings in The Lancet Psychiatry on 16 March 2026, researchers conducted a review of 54 randomised controlled trials (RCTs) published between 1980 and 2025 that evaluated the efficacy of plant-based and pharmaceutical cannabinoids in reducing or treating mental disorders and substance use disorders (SUDs).

In total, the researchers analysed data from 2,477 participants.

A combination of cannabidiol and delta-9-tetrahydrocannabinol — when compared with placebo — produced some “promising findings”, which includes reducing cannabis withdrawal symptoms and cannabis use among those with cannabis use disorder, the authors concluded.

The results also revealed that the combination of cannabidiol and delta-9-tetrahydrocannabinol reduced tic severity among people with tic or Tourette syndrome.

However, the authors highlighted that the analysis showed no significant effects on anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder and opioid use disorder.

The authors said there were “insufficient data” to analyse the use of medical cannabis in treatment of ADHD, bipolar disorder and obsessive-compulsive disorder, and “absence of evidence” for its use in the treatment of depression.

“There is a crucial need for RCTs with larger and more representative samples,” the authors added.

“Given the scarcity of evidence, the routine use of cannabinoids for the treatment of mental disorders and SUDs is currently rarely justified.”

Mike Barnes, founder of the Medical Cannabis Clinicians Society and Cannabis Industry Council, commented: “It’s sad to see yet another negative article based on ignorance about the suitability of cannabis to undergo controlled trials. It cannot be subjected to the classical pharmaceutical model of placebo-controlled, double-blind studies. It is a complex plant with over 500 components, it requires highly personalised dosing and a placebo control is next to impossible.

“If the authors looked at real-world evidence — they only looked at controlled trials — they would come to a different conclusion. There are now about 100,000 cannabis prescribed patients in the UK, and about 30% use it for mental health issues, mainly anxiety. Would those people pay for a prescription out of their own pocket if it didn’t work?”

In its annual report — ‘The safer management of controlled drugs: annual update 2025’ — the Care Quality Commission (CQC) said that there were 346,600 cannabis-based products for medicinal use dispensed between 1 April 2023 and 31 March 2024, an increase of 130% compared with the previous year.

The report said that almost all of these were prescribed in the independent sector, although it did not list the reasons for these prescriptions.

According to the charity Drug Science, which ran a project called T21 from 2020 to 2024 to explore people’s experiences of using medical cannabis, 42% of participants identified “psychiatric conditions” as the primary reason for using the products.