A double-blind, randomized, placebo-controlled trial was conducted to determine the onset of action of ibuprofen 400 mg in the treatment of muscle-contraction headache. Because this represents a non-prescription dosage of this analgesic, we evaluated subjects with a history of recurrent muscle-con-traction headaches that were amenable to over-the-counter analgesic therapy. Headache pain intensity was evaluated on a visual analog scale, and pain relief was measured on a categorical scale 15, 30, 45, 60, 90, and 120 minutes after a single 400-mg dose of ibuprofen or placebo. Efficacy was detected within 15 minutes on the pain intensity rating scale (P<0.05) and within 30 minutes and at all subsequent time points on both the pain intensity and pain relief rating scales (P<0.001). These results indicate an early onset of action of ibuprofen 400 mg in the treatment of muscle-contraction headache.