Aim. To assess the efficacy and safety of using the homeopathic drug Mastopol for the relief of mastalgia in women with infertility, including those associated with endometriosis, as well as to study the drug tolerability and adherence to the treatment, as well as to determine its antiproliferative and analgesic effects in patients of the study cohort. Study design: open-label, randomized, non-comparative, observational study. Material and methods. 79 infertile women with mastalgia (67 with cyclic mastalgia and 12 with acyclic mastalgia) were examined and treated with Mastopol. Mastopol was prescribed 1 tablet 3 times a day sublingually. The course of treatment was 8 weeks. The efficacy of mastalgia relief was assessed using a Visual Analogue Scale (VAS). Treatment outcomes were considered good if pain severity by the VAS decreased by 4 or more points from the baseline levels at the end of Mastopol treatment course. Results. One Mastopol treatment course provided good treatment outcomes in 76,2% of patients with cyclic mastalgia and in 33,3% of patients with acyclic mastalgia. There were no adverse reactions or complications in patients treated with Mastopol. Conclusions. Mastopol has established itself as a quite effective and safe drug in patients of the study cohort; if there is an insufficient effect, Mastopol can supplement traditional pharmacological agents recorded in the current clinical guidelines. © 2021 Federal Informational-Analytical Center of the Defense Industry. All rights reserved.