Background: medical cannabis refers to the use of cannabis or cannabinoids as medical therapy to treat disease or alleviate symptoms. In the United States, 23 states and Washington DC (May 2015) have introduced laws to permit the medical use of cannabis. Within the European Union, medicinal cannabis laws and praxis vary wildly between Countries.
Objectives: to provide evidence for benefits and harms of cannabis (including extracts and tinctures) treatment for adults in the following indications: control of spasticity and pain in patients with multiple sclerosis; control of pain in patients with chronic neuropathic pain; control of nausea and vomiting in adults with cancer receiving chemotherapy.
Methods: we searched the Cochrane Central Register of Controlled Trials, PubMed, and EMBASE from inception to September 2016. We also searched for on-going studies via ClinicalTrials.gov and the World Health Organization and International Clinical Trials Registry Platform (ICTRP) search portal. All searches included also non-English language literature. All relevant randomized controlled trials (RCTs) evaluating the safety and efficacy of cannabis (including extracts and tinctures) compared with placebo or other pharmacological agents were included. Three authors independently evaluated the titles and abstracts of studies identified in the literature searches for their eligibility. For studies considered eligible, we retrieved full texts. Three investigators independently extracted data. For the assessment of the quality of evidence, we used the standard methodological procedures recommended by Cochrane and GRADE working Group.
Results: 41 trials (4,550 participants) were included; 15 studies considered efficacy and safety of cannabis for patients with multiple sclerosis, 12 for patients with chronic pain, and 14 for patients with cancer receiving chemotherapy. The included studies were published between 1975 and 2015, and the majority of them were conducted in Europe. We judged almost 50% of these studies to be at low risk of bias. The large majority (80%) of the comparisons were with placebo; only 8 studies included patients with cancer receiving chemotherapy comparing cannabis with other antiemetic drugs. Concerning the efficacy of cannabis (compared with placebo) in patients with multiple sclerosis, confidence in the estimate was high in favour of cannabis for spasticity (numerical rating scale and visual analogue scale, but not the Ashworth scale) and pain. For chronic and neuropathic pain (compared with placebo), there was evidence of a small effect; however, confidence in the estimate is low and these results could not be considered conclusive. There is uncertainty whether cannabis, including extracts and tinctures, compared with placebo or other antiemetic drugs reduces nausea and vomiting in patients with cancer requiring chemotherapy, although the confidence in the estimate of the effect was low or very low. In the included studies, many adverse events were reported and none of the studies assessed the development of abuse or dependence.
Conclusions: there is incomplete evidence of the efficacy and safety of medical use of cannabis in the clinical contexts considered in this review. Furthermore, for many of the outcomes considered, the confidence in the estimate of the effect was again low or very low. To give conclusive answers to the efficacy and safety of cannabis used for medical purposes in the clinical contexts considered, further studies are needed, with higher quality, larger sample sizes, and possibly using the same diagnostic tools for evaluating outcomes of interest.