HCG is a glycoprotein hormone produced by placental tissue during pregnancy. Structurally similar to LH, it binds LH receptors and triggers the same downstream effects.
Mechanism — Binds Leydig cell LH receptors to drive intratesticular testosterone production and maintain testicular volume. On TRT, exogenous testosterone shuts down LH; HCG replaces the signal, preserving testicular function and fertility.
Use case — Adjunct to TRT (200-500 IU 2-3x/week subcutaneous), fertility preservation, post-cycle therapy. Improves mood and libido in some who feel suboptimal on T alone.
Caveats — Can elevate estradiol — monitor and manage. Supply has been restricted in the US for periods. Don't use without lab monitoring; intratesticular T can be too high.