Background. - Mechanical compression of the trigeminal root by an artery is thought to cause trigeminal neuralgia. The 5- HT1B/1D receptor agonist may inhibit neurogenic inflammation and vasodilation near the irritated trigeminal root. Objective. - To examine the effectiveness of a 5- HT 1B/1D receptor agonist, sumatriptan, on a paroxysmal pain in trigeminal neuralgia. Methods. - Twenty- four patients with trigeminal neuralgia refractory to previous treatment were randomized to receive subcutaneously either 3 mg (1 mL) of sumatriptan or 1 mL of saline placebo. Following a 7- day period, patients crossed over to receive the alternative treatment. Paroxysmal pain triggered by touching or moving the face was assessed with VAS before and 15 minutes after the treatment. Patients used a descriptive scale to pain- grade outcome, and asked to note whether the pain returned and how long after therapy it recurred. Results. - Subcutaneous sumatriptan, but not placebo, significantly decreased VAS from 8.3 ± 2.1 to 2.4 ± 3.0 cm (mean ± SD). The number of patients who described their pain as moderately or slightly better was 20 in the sumatriptan group and 1 in the placebo group. The effect of subcutaneous sumatriptan persisted for a median period of 7.9 hours (range: 1- 20 hours). Conclusions. - Subcutaneous sumatriptan produced prompt analgesia without serious adverse reactions in patients with trigeminal neuralgia refractory to previous treatment. Background. - Mechanical compression of the trigeminal root by an artery is thought to cause trigeminal neuralgia. The 5- HT1B / 1D receptor agonist may inhibit neurogenic inflammation and vasodilation near the irritated trigeminal root. Objective To investigate the effectiveness of a 5- HT 1B / 1D receptor agonist, sumatriptan, on a paroxysmal pain in trigeminal neuralgia. Methods. - Twenty-four patients with trigeminal neuralgia refractory to previous treatment were randomized to receive subcutaneously either 3 mg (1 mL) of sumatriptan or 1 mL of saline placebo. Following a 7- day period, patients crossed over to receive the alternative treatment. Paroxysmal pain triggered by touching or moving the face was assessed with VAS before and 15 minutes after the treatment. Patients used a descriptive scale to pain- grade outcome, and asked to note whether the pain returned and how long after therapy it recurred. Results - Subcutaneous sumatriptan, but not placebo, significantly decreased VAS from 8.3 ± 2.1 to 2.4 ± 3.0 cm (mean ± SD) The number of patients who described their pain as moderately or slightly better was 20 in the sumatriptan group and 1 in the placebo group. The effect of subcutaneous sumatriptan persisted for a median Conclusions. - Subcutaneous sumatriptan produced prompt analgesia without serious adverse reactions in patients with trigeminal neuralgia refractory to previous treatment.