Looking Beyond the Usual Suspects: A Rare Case of Teriparatide-Induced Gynecomastia.

Teriparatide, an osteoanabolic agent, is a biosynthetic analogue of the 1-34 amino acids of human parathyroid hormone (PTH) used for the treatment of osteoporosis. It is typically well-tolerated; common side effects include headaches, arthralgias, nausea, and dizziness. In this report, we present a case of gynecomastia occurring shortly after initiating teriparatide therapy, associated with nipple sensitivity and breast tenderness. Secondary workup for various causes of gynecomastia was unremarkable. Finally, a decision was made to discontinue teriparatide due to the patient's concerns. The nipple sensitivity started improving shortly afterward, with complete resolution of gynecomastia 4 months later. Although this unusual side effect has been reported as a possibility in postmarketing studies, a chronological report on the occurrence of teriparatide-induced gynecomastia and its complete resolution after discontinuing teriparatide has not yet been published in the literature.