Antiemetics are commonly prescribed as prophylaxis for nausea and vomiting when opiate analgesics are prescribed in the emergency department. This prospective, randomized, double-blind, placebo-controlled trial assessed the incidence of nausea and vomiting after morphine and pethidine (meperidine) analgesia, and the effect of metoclopramide on this incidence. Intravenous morphine or pethidine analgesia was administered with metoclopramide or placebo to 122 opiate-naïve patients with acute severe pain. Seven patients (5.7%) experienced nausea, three in the metoclopramide group and four in the placebo group. One patient (0.8%) had vomiting. The frequency of other side effects was higher in the metoclopramide group (7.9% versus 3.4%). None of these differences reached statistical significance. The low incidence of nausea and vomiting after opiate analgesia, and higher incidence of side effects with metoclopramide, are consistent with controlled data in the literature. Prophylactic metoclopramide should not be used routinely in ED patients receiving parenteral morphine or pethidine analgesia.