A major international review has found no evidence that medicinal cannabis effectively treats common mental health conditions, despite a global surge in its use for such purposes. Researchers from universities in Australia and England concluded there was “very little evidence for its efficacy” in treating anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder, or opioid use disorder.
The study, published in The Lancet Psychiatry, analysed 54 randomised controlled trials involving 2,477 participants. It found no significant effects on outcomes for these conditions, and insufficient evidence for attention deficit hyperactivity disorder, bipolar disorder, obsessive compulsive disorder, and tobacco use disorder. There was no evidence at all for depression.
Some evidence suggested medical cannabis could reduce dependence on cannabis, relieve Tourette syndrome symptoms, help with insomnia, and reduce autistic traits, but these findings were based on low-quality evidence. The researchers concluded that “the routine use of cannabinoids for the treatment of mental disorders and substance use disorders is currently rarely justified.”
Sir Robin Murray, professor of psychiatric research at King’s College London, said many people are misled into using cannabis for treatment, adding that “the UK cannabis clinics operate as drug dealers for the middle class.” However, Mike Morgan-Giles of the Cannabis Industry Council argued that real-world evidence consistently shows medical cannabis reduces symptoms for anxiety and PTSD, criticising the study as adding “more heat than light.”
The Advisory Council on the Misuse of Drugs is currently reviewing the impact of cannabis-based product legalisation in the UK since 2018. Prof Owen Bowden-Jones of the Royal College of Psychiatrists stressed that patients must receive accurate information to make informed decisions about their care.
