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‘No evidence’ cannabis can relieve mental disorders

by Kaya Burgess The Times, posted 29 10 2019

Using medicinal cannabis to relieve the symptoms of mental health problems including depression, anxiety and post-traumatic stress disorder cannot be justified by evidence, scientists say.

Researchers looked at the results of 83 studies, which examined 3,000 people, to examine the effect of “medicinal cannabinoids” on six mental health problems. They concluded there was insufficient evidence to support any claims that medicinal cannabis can relieve symptoms, but said there was plenty of evidence showing that cannabis could contribute to depression and anxiety.

They warned: “In light of the paucity of evidence and absence of good-quality evidence and the known risk of cannabinoids the use of cannabinoids as treatments for mental disorders cannot be justified at this time.”

Louisa Degenhardt, a professor at the National Drug and Alcohol Research Centre at the University of New South Wales in Sydney, Australia, and lead author of the study, said: “Our findings have important implications in countries where cannabis and cannabinoids are available for medical use.

“There is a notable absence of high-quality evidence to properly assess the effectiveness and safety of medicinal cannabinoids compared with placebo and until evidence from randomised controlled trials is available, clinical guidelines cannot be drawn up around their use in mental health disorders.”

The findings have been published in The Lancet Psychiatry journal. The studies examined were published between 1980 and last year and included 42 looking at depression, 31 at anxiety, eight at Tourette’s, three at ADHD, 12 at PTSD and 11 at psychosis.

In most of the cases involving depression and anxiety, patients were using cannabis products to treat chronic pain or multiple sclerosis, while the other studies focused on medical cannabinoids treating mental health disorders.

Most examined the use of tetrahydrocannabinol (THC), the main psychoactive constituent of cannabis, while a small number looked at the use of cannabidiol (CBD), an active ingredient in cannabis.

The study found that THC worsened the symptoms of psychosis but could improve anxiety symptoms among patients with other medical conditions, although researchers said this “may have been due to improvements in the primary medical condition”.

Tom Freeman, lead director of the addiction and mental health group at the University of Bath, said that the analysis “highlights the current low quality of evidence for the efficacy and safety of cannabinoids for the treatment of mental health disorders”.

He said: “Given the significant demand for access to these medications from patients, further research is urgently needed to strengthen the evidence. The only way for patients to access these medications at present is through private prescription which require vastly excessive costs, or via the illicit market which carries risk of prosecution as well as unknown product content, quality and safety.”