Overview
A placental glycoprotein hormone that mimics luteinizing hormone, approved for ovulation induction, certain male hypogonadism, and historically cryptorchidism.
How it works
HCG is a hormone normally produced by the placenta during pregnancy. Its medical usefulness comes from a quirk of biology: its structure closely resembles luteinizing hormone (LH), one of the body's own signals for making sex hormones. Because of this resemblance, injected HCG can stand in for LH and switch on the same machinery.
In men, that means HCG can prompt the testes to produce testosterone and to keep functioning, which is why it is used in some forms of low testosterone and to support fertility. In women, it is used in fertility treatment to trigger the release of a mature egg at the right moment. It is given by injection because, as a large protein, it would be destroyed in the digestive tract.
HCG is FDA-approved for specific uses, including ovulation induction in fertility programs and certain cases of male hypogonadism and undescended testicles. It is not an effective or approved weight-loss drug despite popular myths, and its use to maintain fertility during testosterone therapy is common but considered off-label. As a hormone-active agent, it should only be used under medical supervision.
Mechanism · Detailed Analysis
Molecular targetHCG binds the LH/CG receptor (LHCGR), a class-A G-protein-coupled receptor expressed on testicular Leydig cells and ovarian theca and granulosa cells. Its alpha subunit is shared with LH, FSH, and TSH, while the beta subunit confers receptor specificity and an unusually long carboxy-terminal peptide.
Signaling & downstream effectsReceptor activation couples primarily to Gs, raising intracellular cAMP and activating protein kinase A, which upregulates steroidogenic enzymes (including the rate-limiting cholesterol side-chain cleavage step via StAR and CYP11A1). In males this drives Leydig-cell testosterone synthesis; in females it promotes androgen substrate for estrogen production, luteinization, and, at the midcycle surge, oocyte maturation and follicular rupture.
PharmacokineticsHCG is administered parenterally (intramuscular or subcutaneous) because oral delivery is precluded by proteolysis. Its O-glycosylated C-terminal extension confers a notably long circulating half-life relative to pituitary LH, prolonging receptor stimulation. Recombinant and urine-derived preparations are both used clinically.
CaveatsAs an LH mimic, HCG can cause supraphysiologic gonadal stimulation; in women a key risk is ovarian hyperstimulation syndrome, and in fertility cycles multiple gestation. It can interfere with hormone and pregnancy assays. The widely marketed 'HCG diet' has no valid evidence base and the hormone is not approved for weight loss. Hormone-modulating effects warrant clinical oversight.
Published EvidenceLoading cited studies from PubMed…
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Educational aggregation of public literature. Not medical advice and not a recommendation to use any compound. Many compounds here are not approved for human use. Consult a licensed clinician.