Study: Cannabis not an effective treatment for most mental disorders

A recent study has found that cannabis has little effect in treating most mental health and substance use disorders.

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The study, published on Monday in the journal Lancet Psychiatry, evaluated the effectiveness of cannabinoids in managing mental health conditions and substance use disorders by reviewing data from 54 randomised clinical trials conducted between January 1980 and May 2025, involving 2,477 participants.

Medical marijuana includes products with cannabidiol, or CBD, and delta-9-tetrahydrocannabinol, or THC, the part of the plant that produces euphoria.

The researchers from universities in Sydney, Brisbane and Melbourne in Australia and Bath in England concluded there was “very little evidence for its efficacy” in treating anxiety, PTSD, psychotic disorders, anorexia, and opioid use disorder.

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They also said there was insufficient evidence to assess their impact on ADHD, bipolar disorder, OCD, and tobacco use disorder, with no reliable data supporting their use for depression.

The review was prompted by the legalisation of cannabis as a treatment in countries including the US, the UK, Australia and Canada.

However, a combination of cannabidiol and THC, the compound responsible for the “high” associated with marijuana, was found to slightly reduce withdrawal symptoms.

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The study added that cannabinoids increased sleep duration in people with insomnia and showed a modest reduction in autistic traits among individuals with autism spectrum disorder.

However, the researchers noted that cannabis use increased cravings among those with cocaine addiction. They also found that users were more likely to experience general side effects, although the risk of serious adverse events was not higher than in non-users.

The team called for larger and more comprehensive studies, noting that limited data, small sample sizes, and a focus on long-term outcomes may have affected the findings, while gender differences were largely not considered.

They further warned that relying on cannabis-based treatments could delay more effective therapies, stressing that their routine use is rarely justified and recommending stronger regulation, particularly where medical providers may be influenced to promote their use.

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