Marijuana for Painful Peripheral Neuropathy?

In 1999, an Institute of Medicine report concluded that the natural products contained in marijuana (cannabinoids) might be useful for managing pain and spasticity. Now, investigators have conducted a randomized, double-blind, placebo-controlled trial to determine whether smoked marijuana has therapeutic value specifically in HIV-infected patients with painful peripheral neuropathy.

Using a uniform puff procedure, 50 patients smoked marijuana three times daily for 5 days at an inpatient general clinical research center (GCRC) in California. Those assigned to the treatment group smoked active marijuana (grown by the federal government and not very potent by street standards), whereas those assigned to the placebo group smoked marijuana with the cannabinoids removed. The trial incorporated many clever design elements to control for potential confounding, including eligibility criteria that required a history of prior marijuana exposure but did not allow for current substance abuse, a 2-day lead-in phase in the confines of the GCRC, observation of smoking sessions by study staff, and no visitors permitted during the 7-day GCRC stay. All patients rated their chronic neuropathic pain on a daily basis before, during, and after the smoking phase of the study. In addition, 30 patients underwent experimental tests, both before and after smoking, that involved exposing their forearms to heat for 1 minute; these tests allowed for an assessment of marijuana’s effects on acute pain.

At baseline, the groups had similar median daily pain ratings. By the end of the smoking phase, about half of the marijuana group, compared with one quarter of the placebo group, had a clinically significant reduction in chronic pain (defined a priori as >30%). The median daily reduction in chronic pain was 34% in the marijuana group and 17% in the placebo group. During most of the experimental tests, the marijuana group experienced a significantly smaller area of pain than did the placebo group. Sedation, anxiety, disorientation, confusion, and dizziness were all significantly more common in the marijuana group.