Human Chorionic Gonadotropin (hCG)

hCG is a heterodimer built on the same alpha subunit as LH, FSH and TSH, paired with a beta subunit resembling LH beta but carrying an extra carboxy-terminal extension of about two dozen residues with four O-linked sugar chains. That tail is the whole pharmacological story: it slows clearance so much that hCG persists for tens of hours where LH is cleared in tens of minutes. Both act at the same receptor, LHCGR, on Leydig cells, theca cells and the corpus luteum, so hCG is best understood as a long-acting LH.

In early pregnancy hCG roughly doubles every two days before peaking near the end of the first trimester. Its approved uses follow from LH-like activity: triggering final oocyte maturation in assisted reproduction, stimulating testosterone production in hypogonadotropic hypogonadism, and prepubertal cryptorchidism. Because it acts on the gonad rather than the pituitary, hCG maintains intratesticular testosterone where exogenous testosterone suppresses it, and for the same reason WADA prohibits it in male athletes at all times.

The useful distinction is where in the axis a drug acts. hCG drives the gonad directly and does nothing to restore hypothalamic or pituitary function, so it substitutes for a missing signal rather than repairing the loop. It also registers on any pregnancy test.

The most persistent misuse has nothing to do with reproduction. hCG has been sold for weight loss since the 1950s; randomised trials found no effect on weight or hunger beyond the very-low-calorie diet it was paired with, the FDA has long required labelling stating that effectiveness for weight loss has not been demonstrated, and the FDA and FTC acted against homeopathic hCG drops in 2011, yet the protocol still circulates. A quieter error reads an hCG concentration as interchangeable with LH; the receptor is shared, the exposure over time is not.