HCG

Human chorionic gonadotropin, HCG for short, is built from two subunits. The alpha chain is shared with LH, FSH and TSH; only the beta chain makes the molecule HCG and sets its biological effect. The placenta's syncytiotrophoblast produces the glycoprotein hormone during pregnancy.

For research on the hypothalamic-pituitary-gonadal axis, HCG matters for one simple reason: it binds the same receptor as LH but, with a half-life of around 24 to 36 hours, stays in the blood far longer than LH with its few hours. That makes it the tool for modelling LH signalling over longer periods.

At the receptor:

• In the Leydig cells of the testis, binding sets steroid synthesis in motion and testosterone production rises.
• In the theca cells of the ovary, oestrogen production is stimulated.
• A 2012 cell study showed that LH and HCG signal differently through the shared receptor: HCG drove cAMP formation about five times more strongly, whereas LH favoured the ERK and AKT pathways.

Human data: in 29 healthy men, testosterone enanthate cut intratesticular testosterone by 94 percent; adding low-dose HCG kept the value normal, scaling with the HCG dose. A retrospective look at 26 men on testosterone replacement with accompanying HCG found stable semen parameters for over a year and no azoospermia. A 2010 review sorts the hormone into four variants with separate tasks: the free beta subunit as well as regular, hyperglycosylated and pituitary HCG.

We list HCG strictly as a research compound; this text is context, not a guide to use.

HCG is well characterised, but being a gonadotropin it reaches straight into a hormone axis. That sets its risk profile apart from peptides acting locally in tissue:

• Oestrogenic effects: more testosterone also means more aromatisation to oestradiol. Water retention and irritation of breast tissue are described in the literature.
• Axis shift: in preclinical models, sustained stimulation of the LH receptor can alter the body's own regulation; the long half-life makes this more pronounced.
• Injection site: mild redness, pressure or a brief irritation are among the most frequent observations.
• Long-term data: for extended use outside clinical trials there are no robust human data; the profile rests on short-term clinical data and animal models.

This summary is no substitute for medical advice.

• LH and hCG action on the same receptor results in quantitatively and qualitatively different intracellular signalling - 2012 cell study: HCG drives cAMP, LH leans towards ERK and AKT.
• Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppression - randomised 2005 study in 29 healthy men.
• Concomitant intramuscular human chorionic gonadotropin preserves spermatogenesis in men undergoing testosterone replacement therapy - retrospective analysis of 26 men from 2013.
• Biological functions of hCG and hCG-related molecules - 2010 review of the hormone's four variants.