The objectives of this study were to determine the dose response and safety of the oral analgesic cizolirtine citrate (E-4018) in patients with postoperative pain after third molar extraction. This was a placebo-controlled, double-blind, randomised, parallel-group study. Doses of E-4018 were 50 mg, 100 mg, or 150 mg. The primary outcome measure of efficacy was patient assessment of pain severity, determined from serial visual analogue scales (VAS) over a four-hour investigation period. Other efficacy measures included the number of patients taking escape analgesic and the time before it was taken, and an overall assessment of pain relief on a four-point categorical scale. There was no significant difference between any of the E-4018 treatment groups and placebo in terms of the AUC for VAS pain scores over time. The percentages of patients who took paracetamol within five hours of their dose were 100%, 95%, 78% and 82% for the placebo, 50 mg, 100 mg and 150 mg E-4018 groups, respectively. The time to first use of paracetamol was significantly different for the 100 mg and 150 mg E-4018 groups compared to placebo. There were 17 adverse events, of which five were possibly related to the study medication (one in the placebo group and four in the 150 mg E-4018 group). We conclude that there was a dose-related trend in the percentage of patients requiring paracetamol within five hours of their study medication, and in the percentage of patients that recorded the treatment as providing good or excellent treatment of pain. There was, however, no firm evidence of a dose-related analgesic effect over the dose range of Cizolirtine chosen for this study. E-4018 was well tolerated in all patients.