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The Medical Use of Marijuana in Parkinson's Disease
CB1 receptors are densely expressed in the basal ganglia and cortical areas affected in Parkinson's disease (Venderova et al., 2005, Brotchie et al., 2005). Because of this, there is a rationale for usage of THC in the disorder. Also, CBD has been assessed as a potential therapeutic agent for Parkinson’s disease because of its possible neuroprotective attributes (Fernandez-Ruiz et al., 2011). This module will review the available clinical evidence for the use of cannabis in the treatment of Parkinson’s disease and the associated symptoms of Parkinson's disease.
The pioneering neurologist Sir William Gowers described use of an oral cannabis extract preparation for Parkinson's disease in the late 19th century (Gowers, 1888) observing that it might (p. 1012), "quiet the tremor for a time." More interesting was his attestation to its benefit after chronic usage (p. 1013):
In one case, tremor had commenced in the right arm and leg an hour after a railway accident, and extended, three months later into the left arm. Two years subsequently there was constant lateral movement at the wrist joints, but no tremor of the fingers. A great improvement occurred on Indian hemp, and a year later the tremor had almost ceased, being occasional only.
In the modern era, a female patient with Parkinsonian tremor who had failed conventional treatment claimed several hours of relief after smoking cannabis of unspecified composition on three different occasions (Frankel et al., 1990). However, when she and four other treatment-resistant patients with tremor were administered prepared cannabis containing 1 gram of 2.9% THC, no benefit was observed on tremor in any of them in comparison to diazepam, levodopa/carbidopa or apomorphine.
A cannabis extract ("Cannador") in capsules of 2.5 mg of THC and 1.25 mg of CBD was employed to assess dyskinesia associated with Parkinson disease (Carroll et al., 2004). The design was a randomized placebo-controlled crossover trial in 19 patients with each phase lasting four weeks with a two-week intervening washout period. Doses were expressed in mg/kg rather than absolute doses, but a majority of subjects did not attain the "target dose" which would seemingly have been in the range of 15-20 mg of THC. The median dose in this study was THC = 0.17 mg/kg/d. Seventeen patients completed the trial, but no significant benefits nor liabilities on dyskinesia or other PD signs were observed using various objective measures. It was stated that adverse events were not clearly different from placebo despite loss of two subjects and failure to fully escalate dosage to targets.