Purpose Post-operative nausea and vomiting (PONV) is considered as one of the most disturbing sequels of surgeries under general anesthesia, which if not controlled appropriately increases post-operative morbidity, nursing burden, and general healthcare costs. In this study, we compared granisetron with its brand Kytril Ò and also with metoclopramide regarding PONV management. Methods A total of 180 obstetrics and gynecology patients who underwent surgeries under general anesthesia participated in this prospective study at the Dr. Shariati Teaching Hospital, Tehran, Iran. The patients were randomly assigned to single-dose generic granisetron (40 mcg/kg), Kytril Ò (40 mcg/kg), or metoclopramide (0.2 mg/kg) at the end of the surgery. Two episodes of emetic symptoms (nausea and vomiting) were recorded by a gynecologist who had no knowledge of which treatment each patient had received. This gynecologist observed the patients at three different intervals: 0-6, 6-12, and 12-18 h post-surgery. Results One hundred and thirty-seven patients (76.1 %) underwent hysterectomy and 40 patients (22.2 %) underwent myomectomy. Each group consisted of 60 patients (33 %). The incidence of vomiting in the first 6, 12, and 18 h post-surgery was 22, 15.2, and 13.3 % for granisetron; 18.6, 10, and 8.3 % for Kytril; and 22, 11.9, and 5 % for generic metoclopramide, respectively. There was no significant difference in the incidence of PONV with any of these agents. Conclusions All three anti-nausea and vomiting agents, granisetron, its brand (Kytril), and generic metoclopramide, have a similar effect to manage PONV in obstetrics and gynecological surgeries. Trial registration This trial is registered with www.irct.ir, number IRCT201010134927N1.