hCG
A glycoprotein hormone that acts on the LH receptor — a pituitary bypass, not a pituitary signal.
Endocrine · 7 min read · updated 13 Aug 2026
Research use only. The ranges below are what published studies and community protocols report. They are reference material for laboratory research, not medical advice or a recommendation for human or veterinary use.
The compound
hCG
View- Type
- Peptide Hormone (Glycoprotein)
- CAS
- 9002-61-3
- Formula
- C₁₉₀₅H₃₀₁₃N₆₁₅O₆₁₆S₂₆
- Mass
- ~36,700 g/mol
At a glance
- Class
- Glycoprotein hormone, LH receptor agonist
- Structure
- α subunit (92 aa) + β subunit (145 aa), heavily glycosylated
- Molecular weight
- ~36,700 g/mol
- CAS
- 9002-61-3
- Half-life
- ~24–36 h — far longer than LH's ~20 minutes
- Vial size stocked
- 5000 IU
Human chorionic gonadotropin is a two-subunit glycoprotein produced by the placenta. Its α subunit is identical to that of LH, FSH and TSH; the β subunit is what gives it specificity, and hCG-β is close enough to LH-β that hCG binds and activates the same receptor — the LH/hCG receptor on Leydig cells in the testis and theca cells in the ovary.
The functional difference from LH is duration. LH is secreted in pulses and cleared within about twenty minutes. hCG carries far more sialic acid on its glycan chains, which protects it from hepatic clearance and stretches the half-life to a day or more. One hCG administration therefore produces a sustained stimulus where LH produces a brief one.
That is the key to understanding both its usefulness and its limits: hCG substitutes for the pituitary signal rather than restoring it. It acts downstream of the hypothalamic–pituitary axis, so it stimulates the gonad while the axis above it remains suppressed — or becomes more suppressed, since the resulting sex steroids feed back negatively.
Mechanism in detail
- Leydig cells: LH/hCG receptor activation raises cAMP and drives steroidogenesis, principally the StAR-mediated transport of cholesterol into mitochondria — the rate-limiting step in testosterone synthesis.
- Theca cells: the same receptor drives androgen production that granulosa cells aromatise to oestradiol; a bolus at the right follicular stage triggers ovulation, which is the fertility application.
- Testicular volume: sustained receptor stimulation maintains Leydig and Sertoli cell mass. This is why hCG is used to preserve testicular size and intratesticular testosterone in contexts where the pituitary signal is absent.
- Negative feedback: the sex steroids produced feed back on the hypothalamus and pituitary. hCG does not restore endogenous LH secretion — it replaces its effect.
- Receptor desensitisation: continuous high-dose stimulation downregulates the LH receptor. This is the pharmacological reason intermittent dosing outperforms continuous high dosing.
The three distinct research contexts
- Ovulation trigger — a single large bolus, typically 5,000–10,000 IU, timed to follicular maturity. The 5000 IU vial stocked here is exactly one such dose.
- Testicular maintenance during suppression — small, frequent doses in the 250–500 IU range two or three times weekly, aimed at preserving intratesticular function rather than raising serum testosterone.
- Hypogonadotropic hypogonadism — larger doses, 1,000–3,000 IU two or three times weekly, aiming at replacement-level testosterone from the gonad itself.
Units and the reconstitution that follows
hCG is measured in international units of biological activity, not by mass. A 5000 IU vial is a fixed quantity of activity, and every dose is a fraction of it. Because doses in the maintenance context are 250–500 IU — a twentieth to a tenth of the vial — the fill volume has to be chosen so those small fractions are measurable.
Reconstituting 5000 IU into 3 ml — the most a standard vial holds — gives about 1667 IU/ml, at which 1 unit on a U-100 syringe is roughly 16.7 IU. A 250 IU dose is then 15 units: comfortably measurable. Reconstituting the same vial into 1 ml would make that dose 5 units, where half a unit is 25 IU — far coarser resolution for the same dose.
Storage
- Lyophilised: 2–8 °C. Stable for a long period if kept cold and dry.
- Reconstituted: 2–8 °C and used within about 30 days. Reported stability is good, but the protein degrades faster than a short peptide at any given temperature.
- Never freeze reconstituted hCG, and protect from light throughout.
Cautions
- Increased aromatisation of the additional androgen is the most common consequence of over-dosing, and the reason maintenance protocols use small frequent doses.
- Ovarian hyperstimulation syndrome is the serious risk in the fertility context and is dose- and response-dependent.
- LH receptor desensitisation is real and is caused by exactly the dosing pattern people reach for when results seem slow.
- hCG is on the WADA prohibited list for male athletes.
- Any hCG-based assay in the same model becomes uninterpretable.
References & credit
- 1Coviello AD et al., J Clin Endocrinol Metab 2005 — Low-dose hCG maintains intratesticular testosterone during gonadotropin suppression — the source of the 250–500 IU figures.
- 2Cole LA — Reproductive Biology and Endocrinology 2010 — hCG structure, glycosylation and the basis of its extended half-life.
- 3Depenbusch M et al., Eur J Endocrinol 2002 — hCG in hypogonadotropic hypogonadism.
This article was written in-house. Where a dose range reflects community practice rather than a published trial, the community references we consulted are credited above and the article says which is which.