Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 0 0 2026 08 29 1669 1669 Milad Masaeli Anesthesiology and Critical Care Research Center, Isfahan University of Medical Sciences, Isfahan, Iran. & Department of Anesthesiology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. & Water and Electrolyte Research Center, Isfahan University of Medical Sciences, Isfahan, Iran. Kajal Mirzaee Tabar Student of Research Committee, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Meisam Abshenas Jami Kurdistan University of Medical Science, Sanandaj, Iran. 2026 06 18 2026 07 04 Background: Postoperative nausea and vomiting (PONV) are common after cesarean delivery under spinal anesthesia and may impair maternal recovery and early postoperative comfort. Dexamethasone is an established antiemetic, but the optimal prophylactic dose in obstetric patients remains unclear. This study evaluated the dose–response effect of intravenous dexamethasone compared with paracetamol and placebo for the prevention of PONV after cesarean delivery. Methods: In this randomized triple-blind clinical trial, 239 parturients undergoing cesarean delivery under spinal anesthesia were allocated to five groups: placebo, paracetamol 1 g, dexamethasone 2 mg, dexamethasone 4 mg, and dexamethasone 6 mg. The primary outcome was the incidence of PONV during the first six postoperative hours. Secondary outcomes included PONV severity, treatment effect expressed as odds ratios, and dose–response trend across dexamethasone groups. Results: The incidence of PONV was highest in the placebo group at 70%. PONV occurred in 55% of patients receiving paracetamol, 40% receiving dexamethasone 2 mg, 25% receiving dexamethasone 4 mg, and 12% receiving dexamethasone 6 mg. Compared with placebo, paracetamol reduced the odds of PONV, although the effect was smaller than that observed with dexamethasone. Dexamethasone showed a significant dose-dependent reduction in both incidence and severity of PONV. The strongest effect was observed with dexamethasone 6 mg, which was associated with the lowest PONV incidence and no cases of severe vomiting. Conclusion: Intravenous dexamethasone significantly reduced the incidence and severity of PONV after cesarean delivery under spinal anesthesia in a dose-dependent manner. Dexamethasone 4 mg appears to offer an effective balance between antiemetic efficacy and limited steroid exposure, while 6 mg provides the greatest reduction in PONV. Paracetamol showed a smaller antiemetic effect and may be more appropriate as an analgesic adjunct than as a primary antiemetic. https://aacc.tums.ac.ir/index.php/aacc/article/view/1669