Hello and thank you for the great question,
Several preclinical studies demonstrated that modulating the endocannabinoid system may be useful in treating some motor symptoms of Parkinson’s disease. Unfortunately though, results from clinical studies have been inconclusive and conflicting.
However, "an open-label observational study assessing the clinical effect of cannabis on motor and non-motor symptoms of PD revealed significant improvement after treatment in tremor (P < 0.001), rigidity(P = 0.004), and bradykinesia (P < 0.001)."
Also, typical neuropathological features of Parkinson’s include degeneration of dopaminergic neurons; and several studies suggest that cannabis has antioxidant, anti-inflammatory and other properties that could be neuroprotective — which may explain some of the positive results some studies have show regarding cannabis and Parkinson’s.
And although the research regarding cannabis and motor symptoms of PD has been conflicting, cannabis has been shown to mitigate many of the non-motor symptoms which accompany Parkinson’s, such as insomnia, pain, anxiety and depression.
Altogether, for most, I consider cannabis as a valuable adjunctive medicine for the treatment of Parkinson’s, which should improve the quality of life for most patients afflicted with Parkinson’s disease and may even slow the progression of the disease and reduce motor symptoms.