Cannabis is not an effective treatment for common mental health conditions despite a global increase in patients using it for this purpose, a review has found.
The researchers concluded that there is “very little evidence for its effectiveness” in the treatment of anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder or opioid use disorder.
Experts from the universities of Sydney, Brisbane and Melbourne in Australia and Bath in England conducted the largest and most comprehensive analysis to date of the evidence for cannabinoids – cannabis-based therapies – for the treatment of substance abuse and mental health disorders.
Their review was prompted by the legalization of cannabis as a treatment for both types of conditions by countries including the US, UK, Australia and Canada.
Evidence from clinics that distribute marijuana for medical purposes says that mental illnesses such as anxiety and depression are the main reasons described by patients, followed by chronic pain, and some suffer from both.
Medical products can reduce dependence on cannabis, ease the symptoms of Tourette syndrome and help insomniacs sleep better, according to some evidence analyzed by researchers. They appeared to help reduce the autistic characteristics exhibited by those with autism spectrum disorder, although these findings were based on “low” quality evidence.
However, there is no reason to believe that medicinal cannabis has helped combat mental health conditions, the researchers added.
“There were no significant effects on outcomes related to anxiety, anorexia nervosa, psychotic disorders, post-traumatic stress disorder and opioid use disorders,” they wrote after reviewing 54 randomized controlled trials involving 2,477 participants.
There is very little evidence on whether cannabinoids have helped combat attention deficit hyperactivity disorder, bipolar disorder, obsessive-compulsive disorder and tobacco use disorder, and none on whether it has been an effective treatment for depression.
“Given the paucity of evidence, the routine use of cannabinoids for the treatment of psychiatric disorders and substance use disorders is currently rarely justified,” the researchers concluded.
Sir Robin Murray, Professor of Psychiatry at King’s College London, said: “While people like me think that the benefits of cannabis treatment are very limited, and side effects are common, the world does not believe this.
“Boosted by the claims of the cannabis industry and the rapidly growing number of cannabis clinics in the UK, many people have been misled into using cannabis to treat their problems. In my view, UK cannabis clinics are acting as drug dealers for the middle class.”
But a trade body emphasized that cannabis reduces symptoms of anxiety and post-traumatic stress.
Mike Morgan-Giles, CEO of the Cannabis Industry Council, said it is vital that people with mental illness can access the treatment they need.
He added: “Real-world evidence, including T21 findings, consistently shows that medical cannabis reduces symptoms for patients with anxiety and post-traumatic stress.
“Unfortunately, this latest paper adds more heat than light and does not accurately reflect how clinical prescribing is done in the UK.”
The Advisory Council on the Misuse of Drugs, which reports to UK ministers, is conducting a review of how the legalization of cannabis-based products is working in 2018, including “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 overlooked for many conditions.
“While these products have evidence of modest benefit for some addicts, they should not currently be prescribed for many psychiatric disorders for which no benefit has been found.
“It is vital that patients are given accurate and transparent information about these products so that they can make informed decisions about their care and treatment.”
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