Evidence for the use of cannabinoids in Parkinson's disease

Cannabis and synthetic cannabinoid formulations have now been legally approved in several countries for treatment of patients with Parkinson's disease (PD). Hence, PD patients consult physicians more frequently for prescription of cannabinoids to alleviate symptoms that might not respond well to dopaminergic treatment. Despite the increasing volume of research generated in the field of cannabinoids and their effect on Parkinson's disease, there is still paucity of sufficient clinical data about the efficacy and safety in PD patients. There is increasing understanding of the endocannabinoid system, and the distribution of cannabinoid receptors in basal ganglia structures might suggest potential benefit on parkinsonian symptoms. Concerning clinical research, only one of to date four conducted randomized placebo-controlled trials showed an effect on motor symptoms with alleviation of levodopa-induced dyskinesia. There are a growing number of uncontrolled trials and case reports that suggest beneficial effects of cannabinoids in PD patients. However, the variety of substances investigated, the varying routes of intake, differing doses and time courses make it difficult to compare data. We here provide an overview of the current literature in this field and discuss a pragmatic approach for the clinical use of cannabinoids in PD.