Androgens, Anabolic Steroids & Antiandrogens

Introduction & classification

• Androgens — substances that cause development and maintenance of male secondary sex characters; testosterone is the principal natural androgen in both sexes, synthesised by testicular Leydig (interstitial) cells (~5–12 mg/day in the adult male, ~95% testicular + ~5% adrenal).
• Anabolic steroids — synthetic androgens engineered for supposedly higher anabolic and lower androgenic activity — but the dissociation is minimal in humans, so "for all practical purposes, they are androgens."
• Scope of the topic — four families — androgens/anabolic steroids (agonists), antiandrogens (AR antagonists, synthesis inhibitors, 5α-reductase inhibitors), drugs for erectile dysfunction (PDE5 inhibitors, intracavernosal agents) and male contraceptives.
• Natural androgens — testosterone; dihydrotestosterone (DHT); weak adrenal androgens DHEA, DHEA-sulfate and androstenedione (potency ~1/20–1/30 of testosterone, active only after peripheral conversion).
• Synthetic androgens — testosterone esters (propionate, enanthate, cypionate, undecanoate — injectable depot); 17α-alkylated androgens (methyltestosterone, fluoxymesterone, oxandrolone, stanozolol, danazol — orally active but hepatotoxic); mesterolone (oral, less gonadotropin feedback).
• Anabolic steroids & SARMs — nandrolone, oxymetholone, stanozolol, methandienone, oxandrolone; designer "stealth" steroids (THG, norbolethone) evade doping detection. Selective androgen receptor modulators (SARMs) are tissue-selective non-steroidal AR ligands — human-tested but none yet approved.
• Antiandrogens — secretion inhibitors (GnRH analogues, ketoconazole, abiraterone); AR antagonists (flutamide, bicalutamide, nilutamide, enzalutamide, apalutamide, darolutamide, cyproterone, spironolactone); 5α-reductase inhibitors (finasteride, dutasteride).