Background: Menthol is the most important active material in mint and different mechanisms have been suggested for the way mint functions, most of which emphasize its analgesic effect owing to the presence of a group of temporary protein receptors. This study investigates the efficacy of peppermint capsule in the treatment of primary dysmenorrhea, in comparison with Mefenamic Acid and placebo. Materials and Methods: This was a prospective, double-blinded, crossover study and was conducted on 127 girl students studying in Hamadan University of Medical Sciences who had experienced primary dysmenorrhea. Each participant was asked to take one of the drugs including Mefenamic Acid and Mint, starting from the first menstruation for 3 days. At the end of each period, a questionnaire was used to gather information; through the volunteer herself, pain intensity was recorded according to visual analog scale (VAS), duration of pain according to COX questionnaire, and bleeding amount according to pictorial blood loss assessment chart (PBAC) chart (Hygham). Results: Average pain intensity and duration of pain were significantly lower after intake of Mefenamic Acid and Mint (P < 0.05). Average bleeding was significantly lower in those taking Mefenamic Acid capsule than in those taking peppermint extract (P < 0.05). Nausea and diarrhea were lower in the mint group than in Mefenamic Acid group. But analgesic usage was lower in Mefenamic Acid group than in peppermint group (P < 0.05). Conclusions: While the bleeding amount did not significantly change, pain and its severity and all the clinical signs and symptoms decreased after taking peppermint extract. Because the side effect of herbal drugs is lower than other medicinal drugs, using mint is advised for treating dysmenorrhea symptoms.