['To assess the effectiveness of diphenhydramine hydrochloride (Benadryl) in the treatment of patients with idiopathic truncal dystonia.', 'Before-and-after trial.', 'University referral center.', 'Five consecutive patients with idiopathic truncal dystonia who were poorly treated with conventional pharmacotherapies. No patients were withdrawn from the trial for adverse side effects.', 'Treatments with diphenhydramine hydrochloride (50 mg intravenously or up to 500 mg/kg orally). Follow-up for up to 20 months.', 'Dystonia evaluation.', 'Diphenhydramine therapy was associated with minimal side effects, and it was most effective in treating patients with dystonia who experienced lightning jerks. Treatment with intravenous diphenhydramine may have a predictive value on a future response to oral therapy.'] Is diphenhydramine effective in the treatment of idiopathic dystonia?