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Study reports mixed findings on medical efficacy of cannabis

Generic image illustrating medical cannabis

Press release issued: 25 June 2015

A large-scale review that evaluated the medical efficacy of cannabinoids — the active chemical compounds in marijuana — across a range of conditions found there is moderate evidence to support the use of cannabinoids for the treatment of chronic pain and spasticity in patients with multiple sclerosis. The meta-analysis, led by the University of Bristol and published in the Journal of the American Medical Association, analysed the results of 79 different randomised-controlled studies involving more than 6,400 patients to investigate the benefits and side effects of medical cannabinoids.

They found there was only moderate-quality evidence to suggest cannabinoids may alleviate chronic neuropathic or cancer pain and muscle contractions or involuntary movements due to multiple sclerosis. There was lower-quality evidence to suggest that cannabinoids alleviated the symptoms of nausea and vomiting due to chemotherapy, weight gain in HIV, sleep disorders and Tourette syndrome. There was very low-quality evidence to indicate patients treated with cannabinoids showed improvement in anxiety, psychosis and depression.

Cannabinoids were associated with a range of side of effects including dizziness, dry mouth, nausea, fatigue, somnolence, euphoria, vomiting, disorientation, drowsiness, confusion, loss of balance, and hallucination. The team did not find any clear evidence on the benefits or adverse effects from taking particular type of cannabinoids or its mode of administration.

Dr Penny Whiting, a senior research fellow at Bristol’s School of Social and Community Medicine, said: “While we found that most studies indicated cannabinoids were associated with improvements in symptoms, these associations did not determine statistical significance in all studies which may be due to small sample sizes of many of the included studies.

“Further large, robust, randomized clinical trials are needed to confirm the effects of cannabinoids, particularly on weight gain in patients with HIV/AIDS, depression, sleep disorders, anxiety disorders, psychosis, glaucoma, and Tourette syndrome are required. Further studies evaluating cannabis itself are also required because there is very little evidence on the effects and adverse effects of cannabis.”


Cannabinoids for Medical Use A Systematic Review and Meta-analysis’ by Penny F Whiting et al in The Journal of the American Medical Association.

Further information

Further information

Medical cannabis refers to the use of cannabis or cannabinoids as medical therapy to treat disease or alleviate symptoms. Cannabinoids are any compound, natural or synthetic, that can mimic the actions of plant-derived cannabinoids. 

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