Fibrocystic breast disease is the most common benign breast disease in women, and it is necessary to investigate the most effective treatment method to reduce its symptoms. Therefore, the study was conducted to investigate the effect of melatonin supplementation on clinical symptoms and paraclinical outcomes in women diagnosed with fibrocystic breast disease. Investigating the Effects of melatonin supplementation on clinical symptoms and paraclinical outcomes in women diagnosed with fibrocystic breast disease. The present study is a controlled intervention-placebo treatment conducted on women suffering from fibrocystic breast disease aged 18-40. This interventional study was conducted on 66 patients (33 in the intervention group and 33 in the control group). Melatonin supplement of 3 mg was administered to the intervention group and a placebo to the control group for 12 weeks. Patient information, symptoms, and paraclinical outcomes were recorded at the beginning of the study before the intervention and 12 weeks after the intervention. After collecting the data, we analyzed it using SPSS version 16 software and appropriate statistical tests. The findings of this study showed that melatonin administration in patients with fibrocystic breast disease reduced anxiety, depression, improved sleep quality, increased TAC (Total Antioxidant Capacity), and decreased MDA (Malondialdehyde). However, both study groups did not have statistically significant differences in the average pain and hs-CRP before and after the intervention. According to the findings of the study and the identification of the positive effect of melatonin on laboratory indicators and symptoms in patients with fibrocystic breast disease, it is recommended to prescribe melatonin in addition to standard treatment to witness a better and faster recovery, and in this way, the quality of life of patients can be increased.