HCG research monograph — Human Chorionic Gonadotropin as a research peptide hormone

Human Chorionic Gonadotropin (HCG) is a heterodimeric glycoprotein hormone produced primarily by the placental syncytiotrophoblast during pregnancy. It is one of the few compounds in this catalogue that is fully FDA-approved as an injectable pharmaceutical for defined human indications, and has a clinical and research history spanning more than seven decades. Because of its mixed registered-pharmaceutical and contested-cosmetic-use history, the regulatory considerations are unusually important to lay out clearly. This monograph covers the molecular structure, gonadotropin pharmacology, the registered FDA indications, and the regulatory boundaries.

Chemical identity and structure.
HCG is a glycoprotein heterodimer of an α-subunit (92 amino acids, shared with LH, FSH, and TSH) and a β-subunit (145 amino acids, HCG-specific, sharing ~85% identity with LH β-subunit at its N-terminus). The intact molecule is heavily glycosylated; the molecular weight including glycans is approximately 36.7 kDa. The β-subunit's unique C-terminal peptide ("CTP") accounts for its longer half-life vs LH. The pharmaceutical-grade injectable HCG sold in research-vendor catalogues is typically produced either by extraction from the urine of pregnant donors (Novarel and equivalents) or by recombinant DNA technology (Ovidrel).

Mechanism of action.
HCG binds the LH/CG receptor (LHCGR), a seven-transmembrane G-protein-coupled receptor expressed on Leydig cells in the testis, theca and granulosa cells in the ovary, and corpus-luteum cells. LHCGR activation drives cAMP signalling and downstream steroidogenesis — testosterone production in males, progesterone production in females. Because HCG binds the same receptor as LH but with a substantially longer half-life, it functions as a long-acting LH-receptor agonist.

Research applications and the evidence base.
HCG has FDA-approved indications for selected female infertility (induction of ovulation in anovulatory women), male hypogonadotropic hypogonadism, and prepubertal cryptorchidism. Research applications extend into LH-receptor pharmacology, steroidogenesis biochemistry, Leydig-cell biology, and gonadotropin-axis studies in rodent and primate models. There is no FDA-approved indication for weight loss — the FDA has issued repeated warning letters against OTC "homeopathic" HCG weight-loss products as unapproved drugs making unsubstantiated claims.

Regulatory status.
Injectable HCG is prescription-only in the United States and most major jurisdictions. The injectable pharmaceutical formulation is regulated as a drug; HCG urine-test kits for pregnancy detection are regulated as diagnostic devices. The published FDA position is that any OTC HCG weight-loss product is by definition unapproved and misbranded. Researchers using HCG should ensure that their supply chain is appropriately regulated and that the product matches a registered pharmaceutical-grade source.

Research context.
HCG is the canonical long-acting LH-receptor agonist used across reproductive endocrinology research. Researchers studying Leydig-cell steroidogenesis, ovarian follicle biology, or gonadotropin-axis dynamics typically work with pharmaceutical-grade recombinant or urine-derived HCG.

Storage and handling.
Lyophilized HCG vials should be kept refrigerated (2–8 °C) and protected from light. Once reconstituted, the solution is typically used within the package-insert-specified window (usually 30–60 days when refrigerated) and not subjected to freeze-thaw cycles.

Quality and COA considerations.
A meaningful COA should confirm identity via bioassay against an authoritative HCG reference standard, purity and bioactivity (expressed in IU rather than mg — HCG is dosed in international units against the WHO HCG standard), and sterility and endotoxin testing. The IU/mg conversion varies meaningfully between urine-derived and recombinant preparations and should be explicit on the COA.

Research-use note: This monograph is an educational summary of the published research literature on HCG. The compound has FDA-approved indications for selected reproductive-endocrinology conditions; use for weight loss has no FDA approval and is the subject of repeated FDA enforcement actions. Nothing here is medical advice or a usage recommendation.