Piroxicam, a potent inhibitor of prostaglandins, is effective and well-tolerated in the treatment of primary dysmenorrhea. A single 40 mg dose has been shown to rapidly reduce the uterine hypercontractility of primary dysmenorrhea. In clinical trials vs placebo, piroxicam in a dose of 40 mg once daily for two days followed by 20 mg once daily thereafter demonstrated superior efficacy. In more than 1,400 piroxicam-treated menstrual cycles and more than 200 placebo-controlled cycles, a similar incidence of side effects-7% and 8.4% respectively-was observed.