Given the importance of heavy menstrual bleeding (HMB), we investigated the effect of plantain syrup on HMB. This randomized clinical trial was performed on 68 women with HMB who were referred to the traditional medicine clinics of Mashhad University of Medical Sciences. The intervention group received placebo capsule and plantain syrup, whereas the control group received mefenamic acid capsule and placebo syrup in the first 5 days of menstruation for three menstruation cycles. Patients were asked to complete pictorial blood assessment chart one cycle before the intervention and three intervention cycles. Hemoglobin was measured at the beginning and at the end of the study. The results showed that the bleeding duration and severity diminished in both groups. No significant difference was observed between two groups in severity of bleeding after intervention (Cohen's d = .24), but duration of bleeding in mefenamic acid group was reduced significantly in comparison with plantain group (Cohen's d = .57). Although mean hemoglobin alterations in mefenamic acid group had a significant difference before and after the intervention, there was no significant difference between the two groups in mean hemoglobin alterations postintervention. Plantain syrup could be suggested as a complementary treatment for HMB, but further studies are required.