Background: Sumatriptan nasal spray may be particularly useful for patients whose nausea and vomiting preclude them from using oral migraine medication or for patients who prefer not to use an injectable migraine medication. The objective of this study was to evaluate in two clinical studies the efficacy and tolerability of the intranasal form of sumatriptan in the acute treatment of a single migraine attack. International Headache Society-diagnosed adult migraineurs in two randomized, double-blind, parallel-group, multicenter studies (n = 409 and 436) used sumatriptan nasal spray 20 mg, 10 mg, or placebo (2:1:1) for the acute treatment of a single migraine attack at home. Predose and at predetermined postdose intervals, patients recorded headache severity (none, mild, moderate, severe); time to meaningful relief; clinical disability (none, mildly impaired, severely impaired, bed rest required); presence/absence of nausea, photophobia, and phonophobia; and the occurrence of adverse events. Two hours postdose in the two studies, moderate or severe baseline pain was reduced to mild or none in 62 to 63% of patients treated with sumatriptan 20 mg, 43 to 54% of patients treated with sumatriptan 10 mg, and 29 to 35% of placebo-treated patients (p < 0.05 20 mg versus placebo for both studies and 10 mg versus placebo for study 1). Onset of relief relative to placebo began as early as 15 minutes postdose(sumatriptan 20 mg, study 2). Clinical disability at 2 hours postdose was reported as mildly impaired or normal in 72 to 74% of patients treated with sumatriptan 20 mg, 56 to 68% of patients treated with sumatriptan 10 mg, and 47 to 58% of placebo-treated patients (p < 0.05 20 mg versus placebo for both studies). Similar efficacy rates were observed for nausea, photophobia, and phonophobia. The most common adverse event in the active treatment groups was disturbance of taste (bad, bitter, or unpleasant taste). Aside from this event, the pattern and incidence of adverse events did not differ among treatment groups. From these results we determined that sumatriptan nasal spray is a rapidly effective, well-tolerated migraine treatment. The 20-mg dose was effective in treating the entire migraine symptom complex, and the 10-mg dose was less consistently effective.