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The Medical Use of Marijuana in Neuropathies
Neuropathic pain is the most widely studied symptom for the use of medical cannabis. In the past year, several review articles summarizing the effects of cannabis on pain have been published, but all have included trials of prescription cannabinoids as well as herbal cannabis (1-3). This module discusses clinical trials that have reported the effects of smoked or vaporized cannabis on a variety of neuropathic pain conditions.
Yes. One randomized, double-blinded, placebo controlled single dose crossover study involving 16 patients with painful diabetic peripheral neuropathy has been conducted (4). The study was designed to assess the short-term efficacy and tolerability of inhaled cannabis comparing placebo (0% THC), low (1% THC), medium (4% THC), or high (7% THC) doses administered by vaporization of 400mg of plant material. This was reported as equivalent to 0, 4, 16 and 28mg THC respectively; no CBD was present in the cannabis. Specific significant comparisons were tested using repeated measures ANCOVA and differences were found between placebo versus low, medium and high dose (p = 0.031, 0.04 and <0.001 respectively) and high versus low and versus medium (both p<0.001). There was a significant negative effect of the high dose on two of three tests of cognition.
Yes. One study has evaluated the effect of smoked cannabis on 50 patients with HIV-associated sensory neuropathy (5). Subjects (who all had to have had prior exposure to cannabis, but who were not current users) smoked 900mg of herbal cannabis containing either 0% THC (placebo) or 3.56% THC three times daily over 5 days. This equates to approximately 96mg THC per day; the cannabis contained no CBD. Smoked cannabis reduced daily pain by 34% (median reduction; Inter Quartile Range =-71 to -16) vs 17% (IQR=-29 to 8) with placebo (p =0.03). Greater than 30% reduction in pain was reported by 52% of subjects in the cannabis group, and by 24% of subjects in the placebo group. Adverse events included anxiety, sedation, confusion, dizziness, disorientation, paranoia and nausea.
Smoked cannabis for HIV/AIDS neuropathy was also evaluated in a crossover trial among 28 subjects (6). Subjects smoked herbal cannabis (the precise amount is not specified) containing 0% THC (placebo) up to 8% THC based on maximal tolerated dose (26 subjects went up to 8% THC). Pain relief was significantly greater with cannabis than placebo, with 46% achieving at least 30% pain relief with cannabis versus 18% achieving at least 30% pain relief with placebo. Most side effects were mild and self-limited, but two subjects experienced treatment-limiting toxicities. Smoked cannabis was generally well tolerated and effective when added to concomitant analgesic therapy with medically refractory pain. Side effects included concentration difficulties, fatigue, sleepiness or sedation, increased duration of sleep, reduced salivation, and thirst.