[Inhibition of nitric oxide synthase has an analgesic effect in chronic pain]

The efficacy of the inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine hydrochloride (L-NMMA), was tested in 16 patients with chronic tension-type chronic headache. The study was designed as a randomized double-blind, crossover trial. Patients were assigned intravenous infusion of 6 mg/kg L-NMMA or placebo on two days separated by at least one week in a randomized order. Headache intensity was measured on a 100 mm visual analogue scale at baseline and at 30 min, 60 min, and 120 min after start of treatment. L-NMMA reduced pain intensity significantly more than placebo: 120 min after start of treatment, the mean pain score was decreased from 49 to 33 with L-NMMA and from 44 to 40 with placebo (p = 0.01). The present study demonstrates that inhibition of NOS has an analgesic effect in chronic tension-type headache.