The utility of intravenous prochlorperazine (PCZ) in the treatment of nausea, vomiting, and headache may be limited by the akathisia that occurs frequently with the recommended 2-min infusion rate. We tested the hypothesis that decreasing the rate of PCZ infusion to 15 min reduces the incidence of akathisia at 1 hour. This double-blinded, randomized, controlled trial was conducted in the Emergency Department of an academic tertiary-care medical center with an annual census of 95,000 emergency patient visits. We enrolled a convenience sample of adult patients who received 10 mg i.v. PCZ for the treatment of nausea, vomiting, or headache. Subjects were randomized to receive either a 2-min infusion of PCZ (10 mg) followed by a 15-min infusion of saline, or a 2-min infusion of saline followed by a 15-min infusion of prochlorperazine. The incidence of akathisia at 1 hour was measured by using explicit diagnostic criteria. One hundred sixty patients were randomly enrolled into two groups, which were comparable with respect to age, gender, weight, and complaint. Akathisia developed in 31 of 84 patients (36.9%) who received the 2-min infusion of PCZ and in 18 of 76 patients (23.7%) who received the 15-min infusion of PCZ (p = 0.07), a 36% (95% CI, -5% to 61%) relative reduction. The delta from pre-infusion to postinfusion scores between the two groups was not significant (p = 0.19). We conclude that slowing the rate of PCZ infusion does not decrease akathisia.