To assess the efficacy of two different doses of a Psidii guajavae folium extract in the management of primary dysmenorrhea. A double-blinded randomized clinical trial was conducted in 197 women with primary dysmenorrhea. Four intervention groups were defined: two extract doses (3 and 6 mg/day); ibuprofen (1200 mg/day); placebo (3mg/day). Participants were followed-up individually for 4 months. The main outcome variable was abdominal pain intensity measured according to a visual analogue scale (VAS). The average age of participants was 19 years; menarche occurred around age 12 years. Participants had menstrual cycles of 28 or 29 days, with menstruation lasting 5 days and mean of pain intensity of 8.2 on the VAS. During each successive treatment cycle, participants experienced a lower pain intensity score. Multiple regression analysis, after adjusting each cycle for baseline pain, treatment compliance and other variables, showed that the group receiving 6 mg/day extract had significantly reduced pain intensity (p