Medical Cannabis Shows Limited Effectiveness for Mental Health Conditions
Medical cannabis is not an effective treatment for common mental health conditions, according to a comprehensive international review. Researchers have concluded there is "very little evidence for its efficacy" in treating anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder, or opioid use disorder.
Largest Analysis to Date
Experts from universities in Sydney, Brisbane, and Melbourne in Australia, along with Bath in England, conducted the largest and most thorough analysis to date of evidence for using cannabinoids—cannabis-based therapies—to treat substance misuse and mental health disorders. Their review was prompted by the legalization of cannabis as a treatment for both types of conditions in countries including the United States, the United Kingdom, Australia, and Canada.
Evidence from clinics that dispense cannabis for medical purposes indicates that mental illnesses such as anxiety and depression are the primary reasons cited by patients, followed by chronic pain, with some individuals suffering from both conditions simultaneously.
Mixed Findings on Specific Conditions
According to some evidence analyzed by the researchers, medical cannabis products can reduce dependence on cannabis, relieve symptoms of Tourette syndrome, and help insomniacs sleep better. They also appear to help reduce autistic traits displayed by those with autism spectrum disorder, although these findings were based on "low" quality evidence.
However, the researchers emphasized there was no reason to believe medicinal cannabis helped tackle mental health conditions. "There were no significant effects on outcomes associated with anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder and opioid use disorders," they wrote in The Lancet Psychiatry after reviewing 54 randomized controlled trials involving 2,477 participants.
Scarcity of Evidence for Other Disorders
There was insufficient evidence regarding whether cannabinoids helped address attention deficit hyperactivity disorder, bipolar disorder, obsessive compulsive disorder, and tobacco use disorder. No evidence at all was found for its effectiveness as a treatment for depression.
"Given the scarcity of evidence, the routine use of cannabinoids for the treatment of mental disorders and substance use disorders is currently rarely justified," the researchers concluded.
Expert Opinions and Industry Response
Sir Robin Murray, a professor of psychiatric research at King's College London, commented: "While people such as me consider that the therapeutic benefits of cannabis are extremely limited, and the side effects common, the world doesn't believe this. Bolstered by the claims of the cannabis industry and the rapidly increasing cannabis clinics in the UK, many people are misled into using cannabis to treat their problems. In my view, the UK cannabis clinics operate as drug dealers for the middle class."
In contrast, a trade body insisted cannabis does relieve symptoms of anxiety and post-traumatic stress. Mike Morgan-Giles, the chief executive of the Cannabis Industry Council, stated it was vital that patients with psychiatric conditions could access the treatment they needed. He added: "Real-world evidence including findings from T21 consistently shows that medical cannabis reduces symptoms for patients with anxiety and post-traumatic stress. Regrettably, this latest paper adds more heat than light and does not adequately reflect how clinical prescribing is undertaken in the UK."
Ongoing Reviews and Professional Guidance
The Advisory Council on the Misuse of Drugs, which briefs UK ministers, is conducting a review into how the legalization of cannabis-based products in 2018 is working, including any "unintended consequences."
Professor Owen Bowden-Jones, registrar of the Royal College of Psychiatrists, said of the Lancet research: "This rigorously conducted study gives us the clearest indication yet that the benefits of cannabis as a medicine may have been overstated for many conditions. While these products have evidence of modest benefit for some addictions, they should not at present be offered for the many mental illnesses for which no benefit was found. It is vital that patients are provided with accurate and transparent information about these products so that they can make informed decisions about their care and treatment."
