Research-use information only. This page summarises published laboratory and clinical literature on human chorionic gonadotropin. It is not medical advice, and the material supplied by Peptides Lab UK is for laboratory research use only, not for human or veterinary use.
HCG (human chorionic gonadotropin) is a glycoprotein hormone composed of an alpha subunit shared with LH, FSH and TSH, and a beta subunit unique to HCG. Because its beta subunit binds the same receptor as luteinising hormone, HCG acts as an LH analogue — which is the property that makes it a reference tool in reproductive endocrinology research. This page is the central HCG reference for UK researchers.
What HCG is
HCG is produced by the syncytiotrophoblast following implantation, and its physiological role is to sustain the corpus luteum so that progesterone production continues through early pregnancy. Structurally it is a heterodimer: a 92-amino-acid alpha subunit common to the glycoprotein hormone family, and a 145-amino-acid beta subunit that determines receptor specificity.
The beta subunit carries a C-terminal peptide extension not present on LH. That extension is heavily glycosylated and substantially slows renal clearance, which is why the reported circulating half-life of HCG is considerably longer than that of LH — a difference that matters when interpreting study design.
How HCG is described to work
HCG binds the LH/choriogonadotropin receptor (LHCGR), a G-protein-coupled receptor expressed on Leydig cells in the testis and on theca and granulosa cells in the ovary. Receptor activation raises intracellular cAMP and drives steroidogenesis through the StAR protein and the downstream enzymatic cascade.
- In male models — LHCGR activation on Leydig cells stimulates testosterone production. Because the signal acts directly at the gonad, it bypasses the hypothalamic-pituitary component of the axis.
- In female models — HCG is used in the literature as an ovulation trigger, substituting for the endogenous LH surge because of its receptor cross-reactivity and longer half-life.
For the wider receptor context, see our reference on peptides in reproductive biology research.
HCG compared to related compounds
HCG is frequently confused with compounds that act at different points in the same axis. The distinction matters:
- HCG vs Gonadorelin — gonadorelin is a GnRH analogue acting at the pituitary, stimulating endogenous LH and FSH release. HCG bypasses the pituitary entirely and acts at the gonad. See gonadorelin acetate.
- HCG vs Kisspeptin-10 — kisspeptin acts further upstream still, at KISS1R on GnRH neurons, driving the pulse generator. See kisspeptin-10.
- HCG vs HMG — human menopausal gonadotropin supplies FSH and LH activity together, whereas HCG supplies LH-like activity alone. See HMG.
In short: kisspeptin acts on the hypothalamus, gonadorelin on the pituitary, HCG on the gonad. Study designs that conflate them are not comparable.
Dosage as described in the research literature
Published protocols describe HCG in international units rather than milligrams, reflecting its measurement by bioactivity rather than mass. Reported research ranges vary widely by species, model and endpoint, and the literature does not converge on a single figure. Reconstitution is with bacteriostatic water, and because HCG is a glycoprotein rather than a short peptide it is more sensitive to handling than most of the research-peptide catalogue.
These figures describe research documentation only and are not instructions for human use. For general preparation mechanics see our peptide reconstitution calculator.
Storage and stability
Lyophilised HCG is stored at 2–8°C or below; reconstituted solution is refrigerated and has a materially shorter usable window. Glycoprotein hormones are more vulnerable to loss of bioactivity through freeze-thaw cycling and agitation than small peptides, so aliquoting after reconstitution is standard practice in study protocols. Loss of bioactivity is not visible in the vial — which is why batch-level Certificate of Analysis data matters more here than for simpler sequences.
Safety signals in the research record
- Ovarian hyperstimulation is the most consistently documented risk in the clinical literature where HCG is used as an ovulation trigger.
- Receptor desensitisation — sustained LHCGR stimulation is reported to downregulate receptor responsiveness, a central consideration in protocol design.
- Assay interference — HCG is the analyte in standard pregnancy testing, and its presence confounds those assays.
The UK regulatory position
HCG is a prescription-only medicine in the UK when supplied for human use. Peptides Lab UK supplies HCG for laboratory research only, correctly labelled, and not for human or veterinary administration. Because HCG is measured by bioactivity rather than mass, and because glycoprotein integrity is not visually assessable, insist on batch-specific Certificate of Analysis documentation and third-party verification. Our full quality-standards SOP sets out the HPLC, mass spectrometry and endotoxin testing applied to every batch.
Frequently asked questions
What is HCG?
Human chorionic gonadotropin, a glycoprotein hormone made of an alpha subunit shared with LH, FSH and TSH, and a unique beta subunit. It binds the LH receptor, which is why it functions as an LH analogue in research settings.
How does HCG work?
It binds LHCGR on Leydig cells in the testis and theca and granulosa cells in the ovary, raising intracellular cAMP and driving steroidogenesis. It acts directly at the gonad rather than through the pituitary.
What is the difference between HCG and gonadorelin?
Gonadorelin is a GnRH analogue acting at the pituitary to stimulate endogenous LH and FSH release. HCG bypasses the pituitary and acts directly at the gonadal LH receptor. They occupy different positions in the same axis and are not interchangeable.
Why is HCG measured in IU rather than mg?
Because it is a glycoprotein whose activity depends on glycosylation state as well as amino acid sequence, potency is standardised by bioactivity rather than mass.
How should HCG be stored?
Lyophilised material at 2–8°C or below; reconstituted solution refrigerated with a materially shorter usable window. Glycoproteins lose bioactivity through freeze-thaw cycling and agitation, so aliquoting is standard.
Is HCG legal in the UK?
HCG is a prescription-only medicine for human use in the UK. Supply for laboratory research, correctly labelled and not for human administration, is a separate lawful category.
Disclaimer: this content is for educational and research purposes only. HCG supplied by Peptides Lab UK is not intended for human or veterinary use.
