HCG

Human chorionic gonadotropin (hCG) is a large placental glycoprotein hormone, not a synthetic peptide — a ~36.7 kDa heterodimer of a shared alpha subunit (also in LH, FSH, TSH) and an hCG-specific beta subunit, about a third of its mass carbohydrate, which gives it a long circulating half-life. Pharmaceutical hCG is urinary-derived (Pregnyl, Novarel) or recombinant (choriogonadotropin alfa, Ovidrel) and is an FDA-approved prescription drug for specific reproductive uses. Critically, those approved uses are distinct from the popular "hCG diet" and unsupervised TRT-adjunct uses — the FDA states plainly that hCG is not effective for weight loss.

hCG is a high-affinity agonist at the LH/choriogonadotropin receptor (LHCGR) on testicular Leydig cells and ovarian theca/granulosa cells. By mimicking LH, it drives the Gs-cAMP-PKA pathway that stimulates testosterone synthesis in men and progesterone production / final oocyte maturation in women. In men it can bypass a deficient pituitary signal to stimulate the testes directly and maintain intratesticular testosterone — one cited study found intratesticular testosterone fell only ~7% with low-dose hCG plus testosterone versus ~94% with testosterone alone.

hCG has decades of human use and three FDA-approved indications per the label: prepubertal cryptorchidism, selected male hypogonadotropic hypogonadism, and ovulation induction in pretreated anovulatory women. A substantial andrology literature supports off-label use to preserve or restore spermatogenesis in men on testosterone or recovering from anabolic-steroid use. By contrast, the evidence for weight loss is negative: the FDA label states there is no substantial evidence hCG increases weight loss beyond caloric restriction, and the FDA/FTC acted to remove illegal OTC "homeopathic" hCG weight-loss products.

For approved uses under supervision, hCG has a well-defined profile: injection-site reactions, headache, fatigue, mood changes, edema and gynecomastia (males). Serious but less common risks include ovarian hyperstimulation syndrome and multiple gestation in fertility use, thromboembolism, and precocious-puberty signs in boys treated for cryptorchidism. The larger real-world hazard is the hCG diet, which pairs the hormone with a ~500-calorie regimen (risking gallstones, electrolyte and cardiac problems) for a use the FDA deems ineffective. hCG is WADA-prohibited in male athletes at all times because it raises endogenous testosterone. YMYL note: prescription-only; nothing here is dosing or treatment guidance.