A 58-year-old postmenopausal woman developed new-onset vaginal bleeding six weeks after initiating semaglutide, with onset correlating to dose escalation to 0.5 mg weekly. Hemoglobin dropped from 12.9 to 10.8 g/dL. Critically, FSH remained elevated at 68.4 mIU/mL and estradiol stayed suppressed at 3.5 pg/mL — ruling out hormonal reactivation. Malignancy, structural pathology, and coagulopathy were excluded. Bleeding fully resolved within five weeks of discontinuation, yielding a Naranjo score of 6 (probable adverse drug reaction).
The proposed mechanism is metabolically elegant and underappreciated: rapid semaglutide-induced adipose tissue reduction may transiently destabilize peripheral estrogen metabolism — specifically aromatase activity in shrinking fat depots — creating local endometrial fluctuations despite systemically stable hormone levels. Adipose tissue is the primary postmenopausal estrogen source, converting androgens to estrone via aromatase, so abrupt adipose loss could produce unpredictable endometrial estrogen exposure independent of serum measurements.
This is a single case report — the lowest rung of evidence — and causality cannot be firmly established. However, its clinical importance is disproportionate to its size. With GLP-1 agonist prescriptions surging globally, postmenopausal women represent a growing treatment demographic. Clinicians must recognize that semaglutide-associated bleeding demands malignancy-first evaluation; dismissing it as drug-related without workup would be dangerous. This report fills a genuine gap: gynecological adverse effects of GLP-1 agonists have not been systematically characterized, making this an important signal for pharmacovigilance registries.