Complementary medicine use and costs in patients with breast cancer who experienced treatment-related side effects: A cross-sectional survey in Korea.

•Treatment-related side effects affect the patients’ life in many ways.•This study aims to investigate the economic impact of treatment-related side effects.•Patients reported substantial economic burden of using complementary medicine and productivity loss due to treatment-related side effects.•Strategies for guiding patients to receive evidence-based and cost-effective complementary medicine are needed.