Dysmenorrhea is among the most common gynecological complaints. There are several mechanisms which initiate dysmenorrhea. Therefore, different compounds can be employed to control its symptoms. NSAIDs such as ibuprofen are highly used in modern medicine to relieve the pain in short-term therapy. This method is not acceptable for long-term therapy due to side effects. Our previous data showed that FENNEL essential oil (FEO) could reduce the frequency and intensity of contraction of rat uterus in isolated organ models. Furthermore, the use of FEO is strongly recommended in traditional medicine for the relief of dysmenorrhea symptoms. Clinical study of FEO in primary dysmenorrhea showed that the essence reduces pain and some of following sequelae side effects noticeably.