Reviewing the current medical literature on this subject shows that there is not yet any definitive answer from a clinical science perspective. Some studies have shown promising results, others have failed to confirm them. But current folk-medicine is full of descriptions of the benefits of cannabis in various neurologic disorders, including Parkinson's disease. You can easily find YouTube videos of Parkinson's disease patients with a visible decrease in their motor symptoms after using cannabis. It's hard to know what to make of that kind of demonstration, but any Parkinson's disease patient would find it compelling. I suggest that although the subject requires lots of additional investigation, the general lack of toxicity of cannabis makes cautious personal experimentation a reasonable thing to do in this situation. Although there is no established protocol for using CBD in Parkinson's disease, there has been no indication of adverse effects and it is a very well tolerated substance in the body. People commonly take daily amounts anywhere from 2mg to 200mg, but there is little or no scientific information relating specific doses to any specific effects - as I said, it is still largely folk-medicine. Much of the reported benefit of medicinal cannabis in Parkinson's disease has involved preparations containing THC also, and my own review of the subject inclines me to agree with that approach.
CBD is a very important compound in both the brain and the rest of the body. The main function of Endocannabinoid system is to regulate and balance all the other cellular processes, which makes all the processes clearer. And when deficiencies occur in the system, CBD can be used to treat them.
In Parkinson’s, the substantia nigra loses from 50-80% of its neurons before symptoms occur. This is thanks to an evolutionary trick your brain picked up somewhere in the last 3 million years called plasticity. Plasticity is the ability of neurons to rewire themselves in the case of damage or disease. CBD and phytocannabinoid-rich mixtures are powerful in promoting neuroplasticity by augmenting (adding to) the activity of the endocannabinoid system. The endocannabinoid anandamide is a key player in the rerouting of neural pathways.