Studies have shown that cannabinoids have limited benefit in the management of acute pain but may be efficacious in controlling spasticity and neuropathic pain. Moreover, newer cannabinoids may have fewer psychotropic effects. Karst and colleagues assessed the efficacy and safety of 1′, 1′Dimethylheptyl-Δ8-tetrahydrocannabinol-11-oic acid (CT-3), a synthetic analog of tetrahydrocannabinol, in the treatment of chronic neuropathic pain.

The study included 21 patients 29 to 65 years of age who had a clinical presentation and examination consistent with chronic neuropathic pain with hyperalgesia and allodynia. The five-week trial was a randomized, double-blind, placebo-controlled, crossover study. Weeks 1 and 4 were baseline weeks, weeks 2 and 5 were intervention weeks, and week 3 was a washout period. Patients were randomized to receive CT-3 or placebo, and pain was measured using a visual analog scale and a verbal rating scale in the morning and the afternoon of each treatment day.

Of the 21 patients, 10 initially received CT-3 and 11 received placebo; after crossover, this relationship was reversed. Results of the testing conducted in the morning (three hours after intake of the study drug) showed significant reduction in pain scores and a strong tendency toward significant pain reduction as measured by mean differences in visual analog scale and verbal rating scale over time. The afternoon results (eight hours after morning intake of the study drug) demonstrated less marked effects. The most common reported adverse effects were tiredness and dry mouth, but patients also had decreased concentration, dizziness, more pain, and sweating.

This study shows that CT-3, given in daily dosages of 40 and 80 mg, is more effective than placebo in the treatment of neuropathic pain, with greater pain-reducing effects at three hours after intake than at eight hours. The amount of pain reduction is greater in patients with lower baseline pain levels. This finding is consistent with the observation that mild pain is easier to reduce than severe pain.