Snapshot A 31-year-old man presents to his primary care physician for the evaluation of infertility. He and his wife have been trying to become pregnant for over a year. His wife was extensively evaluated, which showed no reason on her end for their inability to conceive. Upon further questioning, the patient reports decreased spontaneous erections, breast discomfort, and a reduced need to shave. On physical examination, the patient has a eunuchoid body habitus, gynecomastia, and small testes. On laboratory testing, there is a elevated follicle-stimulating hormone (FSH) and luteinizing hormone (LH) with a low testosterone level. The patient is prescribed testosterone replacement therapy after testing his hematocrit and prostate-specific antigen (PSA) level. (Klinefelter syndrome) Introduction Mechanism of action testosterone has 3 modes of action (based on its structure or its derivatives) login to view 5 more bullets Clinical use testosterone should only be administered in a man who is hypogonadal primary hypogonadism login to view 2 more bullets secondary hypogonadism login to view 5 more bullets anabolic steroid abuse login to view 17 more bullets Adverse effects masculinization in females prostate disorders (e.g., benign prostatic hyperplasia) worsening of sleep apnea erythrocytosis testicular atrophy in males premature closure of epiphyseal plates in adolescents worsening of lipid profile login to view 1 more bullet hepatic adenoma login to view 2 more bullets