The Effect of Fennel on Pain Relief in Primary Dysmenorrhea: A Systematic Review of Clinical Trials

Background and aims: Fennel is often advocated for primary dysmenorrhea. Whether this herb has areal effect on pain relief is still a matter of debate in medicine. Therefore, this study was conducted toevaluate the effect of fennel on primary dysmenorrhea.Methods: This systematic review was conducted on clinical trials (non-randomized, randomized,historical study with concurrent control) published in PubMed (MEDLINE), Web of Science, Scopus,Cochrane Central Register of Controlled Trials (CENTRAL), ProQuest, and Persian databases (Magiran,IranMedex, SID, Irandoc) regarding the effect of fennel on pain intensity in primary dysmenorrhea from1990 to 2019. Nine studies met all inclusion criteria. Any clinical trials on young women with primarydysmenorrhea were included in the study. Studies that used fennel plus other products investigatedfennel effect on premenstrual syndrome (PMS) and bleeding; studies without a control group andnonclinical trials were excluded. In all studies, participants were young female university or highschool students. All of them had moderate to severe primary dysmenorrhea.Results: In all of the studies except for one, fennel had been more effective than placebo in pain relief(P < 0.01). Non-steroidal drugs had the same result as fennel for pain relief. However, in one study,the difference between non-steroidal anti-inflammatory drugs (NSAIDs) and fennel in pain relief wasobserved. Only one study reported increasing vaginal bleeding after fennel consumption in somecases.Conclusion: Collectively, these studies favored fennel over NSAID, other herbal drugs, and placebo.But more investigation is needed to draw a firm conclusion.Registration: PROSPERO - 42015023725