Note: if you enter Cannabidiol into the Pub Med field, there are 1721 articles shown for treating a wide variety of diseases, most in some way connected to nervous system disorders but also the dopaminergic neuronal system (which may malfunction in Parkinsons').
Another substance with potential for treating many ailments is thymoquinone, the active ingredient in Black Cumin seed oil (Nigella Sativa, an Ayurvedic remedy, but available throughout he Middle East and S. Western Asia. "Thymoquinone" has 713 entries in Pub Med, but if you enter "Thymoquinone Parkinson's" into the field, 7 articles come up. There is a remarkable overlap between the influences of Thymoquinone and Cannabidiol. https://www.ncbi.nlm.nih.gov/pubmed/?term=thymoquinone++Parkinson%27s https://www.ncbi.nlm.nih.gov/pubmed/?term=thymoquinone++Parkinson%27s