D-Methionine is a stereoisomer of an essential proteinogenic sulfur-containing amino-acid L-methionine. D-methionine is an antioxidant, it demonstrated protective effects on cisplatin-induced anorexia and renal injury, and protected normal cells from radiation-induced cell death and from radiation-induced mucosal injury. In animal models, it protected against hearing loss induced by cisplatin, carboplatin, aminoglycosides, or noise exposure. A phase 3 clinical trial of D-methionine for prevention of hearing loss was conducted by the US Army, the study was terminated and no results were reported.