More research needed to determine if medicinal cannabinoids improve mental health

Current research is lacking to support claims that cannabinoids improve depressive disorders and symptoms, anxiety disorders or ADHD, according to results of a systematic review and meta-analysis published in Lancet Psychiatry.

“Our findings have important implications in countries where cannabis and cannabinoids are being made available for medical use,” Louisa Degenhardt, PhD, of the National Drug and Alcohol Research Centre at the University of New South Wales Sydney, said in a press release. “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 randomized controlled trials is available, clinical guidelines cannot be drawn up around their use in mental health disorders.”

Degenhardt and colleagues noted that previous research into the use of medicinal cannabinoids for mental disorders has been limited by study designs, use of quantitative synthesis and coverage of mental disorders. They considered all studies that examined any type or formulation of a medicinal cannabinoid in adults aged 18 years or older for treating depression, anxiety, ADHD, Tourette syndrome, PTSD or psychosis.

Of 83 eligible studies that had data for 3,067 patients, the researchers included 42 for depression, 31 for anxiety, eight for Tourette syndrome, three for ADHD, 12 for PTSD and 11 for psychosis. They found that in seven studies, pharmaceutical tetrahydrocannabinol (THC) with or without cannabidiol (CBD) improved anxiety symptoms among patients with other medical conditions, primarily chronic non-cancer pain and multiple sclerosis (standardized mean difference [SMD] = –0.25; 95% CI, –0.49 to –0.01). However, the quality of the evidence based on the Gradings of Recommendations, Assessment, Development and Evaluation approach was very low. In a single study, pharmaceutical THC with or without CBD worsened negative symptoms of psychosis (SMD = 0.36; 95% CI, 0.1-0.62). It did not significantly affect any other primary outcomes for the mental disorders examined but it did increase the number of people who experienced adverse events in 11 studies, compared with placebo across all mental disorders examined, according to the researchers. Overall, few randomized controlled trials examined the role of medicinal cannabis or pharmaceutical CBD.

“In countries where medicinal cannabinoids are already legal, doctors and patients must be aware of the limitations of existing evidence and the risk of cannabinoids,” Degenhardt said. “These must be weighed when considering use to treat symptoms of common mental health disorders. Those who decide to proceed should be carefully monitored for positive and negative mental health effects of using medicinal cannabinoids.” – by Joe Gramigna

Disclosures: Degenhardt reports untied investigator-driven educational grants from Reckitt Benckiser, Mundipharma and Seqirus. Please see the study for all other authors’ relevant financial disclosures.