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Background and Importance Calcitonin gene-related peptide (CGRP) antagonists represent a major advance in the preventive treatment of chronic migraine, particularly for patients who have not responded to conventional therapies. Atogepant, an oral CGRP receptor antagonist, has demonstrated good efficacy and tolerability in clinical trials. However, as a recently marketed drug, its safety profile in real-world use remains under continuous evaluation. To date, menstrual disorders have rarely been described as adverse drug reactions (ADRs) related to CGRP antagonists. Reporting such unexpected events is essential to expand current knowledge and ensure safer use of these agents in women of reproductive age.Aim and Objectives To describe a case of prolonged menstrual bleeding associated with the use of atogepant in a patient treated for chronic migraineMaterial and Methods This descriptive case report was identified through the Outpatient Pharmaceutical Care Unit of a tertiary hospital. The suspected ADR was notified to the Pharmacovigilance System for Medicines for Human Use (PVS-H). Causality was assessed using the Naranjo algorithm. Clinical data were obtained from medical records and patient interviews.Results A 32-year-old woman, non-smoker and without relevant medical history, was followed by the Neurology Department for chronic migraine since 2021. After failure of amitriptyline, flunarizine, topiramate, and botulinum toxin, atogepant 60 mg daily was initiated in August 2024. Three months later, migraine frequency had improved, but the patient reported continuous menstrual bleeding since treatment onset. No concomitant medications or lifestyle changes were identified. Atogepant was discontinued in November 2024, and bleeding resolved within days. The event was classified as a probable ADR according to Naranjo’s scale and reported to PVS-H. Subsequent treatment with fremanezumab caused mild local reaction, and erenumab was later introduced with good efficacy and safety.Conclusion and Relevance Spontaneous reporting of suspected ADRs is crucial to detect and assess rare or previously unreported effects of new therapies. This case highlights a potential association between atogepant and prolonged menstrual bleeding, underlining the importance of post-marketing pharmacovigilance to better define the safety of CGRP antagonists.Conflict of Interest No conflict of interest