Author Affiliations: Department of Medicine, Division of Endocrinology, University of Texas, Southwestern Medical Center, Dallas; and Dallas Veterans Affairs Medical Center, Dallas, Texas.
Testosterone has a variety of well-known effects including bone accrual, building and maintaining muscle mass, and promoting erectile function and libido.1 Of the 5 mg of testosterone manufactured daily by the testes, about 6% to 8% is metabolized by 5α-reductase to make 0.3 mg of dihydrotestosterone (DHT).2 Local conversion of testosterone to DHT by 5α-reductase in the skin and prostate can create locally high concentrations of the potent androgen DHT. Dihydrotestosterone stimulates prostate growth and may promote scalp hair loss. 5α-Reductase inhibition is the principal treatment for benign prostatic hypertrophy but the ramifications of treatment with drugs that inhibit this enzyme on the effects of androgen on the many tissues it influences is incompletely understood.
Gruntmanis U. The Role of 5α-Reductase Inhibition in Men Receiving Testosterone Replacement Therapy. JAMA. 2012;307(9):968-970. doi:10.1001/jama.2012.259