This study aims at evaluating of the Tahiti lemon juice (Citrus latifolia) effects as an alternative and natural treatment to menstrual disorders,1-2 such as dysmenorrhea (strong pain) and menorrhagia (excessive bleeding).3 Flavonoids are the main metabolites found in Citrus species4,5 and taking account their anti-inflammatory activity6 it is expected that the lemon juice mechanism acts inhibiting the inflammatory cascade in the menstrual process. To achieve this purpose a 2D LC–MS/MS was applied to quantify PGE2 and PGF2α, inflammatory mediators, in menstrual fluid.8,9 Two groups of patients were evaluated: control group (CG) and treated with Tahiti lemon juice (LG). Menstrual fluid was collected using menstrual cup collectors. The samples were submitted to centrifugation, dilution, partial precipitation of proteins, and then injected in the online SPE (OASIS HLB column) coupled to UHPLC-ESI-MS/MS (triple quadrupole analyzer) to quantify prostaglandins. And in order to identify the main flavonoids presents in Tahiti lemon juice, a fresh squeezed juice was submitted to centrifugation, off-line SPE (OASIS HLB cartridges) cleanup, and analyzed in UHPLC-ESI-MS/MS (Q-TOF analyzer) and then compared to the standards. The 2D LC-MS/MS method validation was carried out and successfully achieved, according with European criteria.7 The identification of both prostaglandins was based on the ratio analyte/internal standard SRM ions transition, and the concentrations range was found: 6.3 to 91.7 ng mL-1 to PGE2 and 23.7 to 197.7 ng mL-1 to PGF2α. The data show that concentration of PGF2α increases about 60% in the LG, when compared with the CG, while concentration of PGE2 presents a slight decrease (Figure 1). It was observed in the patients of LG a decrease in menstrual bleeding and considering the increase of PGF2α level found in this same group, the hypothesis here suggest that the menstrual bleeding could be controlled by PGF2α vasoconstrictor action,8,9 which blocks the blood passage in the spiral arteries in the uterus wall. And not based on inhibition of the prostaglandins biosynthesis, such expected by the flavonoids anti-inflammatory activity. The lemon juice flavonoids have been identified in comparison to the standards fragmentation and until this moment were found: eriocitrin, hesperidin, rutin and naringin.