BACKGROUND: Recently, the US Food and Drug Administration approved a new oral selective estrogen receptor downregulator for breast cancer, namely, elacestrant (Orserdu). This study aimed to analyze the signals of adverse events (AEs) within the introduction of elacestrant to the market using the FDA Adverse Event Reporting System (FAERS) database. METHODS: Reports on the AEs of elacestrant after its marketing were obtained from the FAERS database. Disproportionality was analyzed using the reporting odds ratio to calculate the magnitude of the risk of the target drug and the AE combination, and the proportional reporting ratio to quantify the strength of the association between the drug and the AEs. RESULTS: A total of 3132 reports on elacestrant-related AEs were obtained, with disease progression, drug ineffectiveness, product dose omission, arthralgia, asthenia, increased tumor marker levels, and bone pain (Number of reported cases (a) ≥ 3 and lower limit of 95% confidence interval >
1) being the high-frequency events not mentioned on the drug label. The top three total frequencies at the system organ class level comprised general disorders and administration site conditions, gastrointestinal disorders, and musculoskeletal and connective tissue disorders. CONCLUSIONS: FAERS data analyses were conducted to evaluate the safety of post-marketing clinical use of elacestrant and to ensure that physicians identify the risk factors for the AEs of this drug.