BACKGROUND Pain is among the most cited negative effects of orthodontic treatment. Non-steroidal anti-inflammatory drugs seem to be an effective option for minimizing this but can have adverse effects on tooth movement owing to their ability to block prostaglandin synthesis. Acetaminophen has been suggested as the analgesic of choice during orthodontic treatment as it showed no effect on orthodontic tooth movement in previous animal studies. The purpose of this study was to compare the effects of ibuprofen and acetaminophen on the prostaglandin E2 (PGE2) levels of the gingival crevicular fluid (GCF) during orthodontic tooth movement in human subjects. METHODS A total of 42 patients (mean age 18±4.5 years) were randomly divided into three equal groups: ibuprofen, acetaminophen, and control groups. Maxillary canines were distalized with 150 g of force delivered by NiTi coil springs. GCF samples were obtained before (baseline) and after spring activation at 24, 48, and 168 h. The PGE2 content of the GCF was determined using enzyme-linked immunosorbent assay. RESULTS PGE2 levels in all groups increased significantly by 24 and 48 h of force application and decreased to baseline levels by 168 h. No significant difference was found between the acetaminophen and control groups at any time point. There was a significant decrease in PGE2 levels in the ibuprofen group at 24 and 48 h when compared to the other two groups. CONCLUSIONS Acetaminophen showed no significant effect on prostaglandin synthesis and may be the safe choice compared to ibuprofen for relieving pain associated with orthodontic tooth movement.