What Is HCG? The Pregnancy Hormone Explained
Hormonal, Growth Hormone & Body Composition Research
HCG (human chorionic gonadotropin) is a glycoprotein hormone, a protein with sugar chains attached, made by the placenta in pregnancy, and it acts on the reproductive system through the same receptor as luteinising hormone (LH), the pituitary signal that drives the ovaries and testes. It is the hormone pregnancy tests detect, its scientific history runs back to the pregnancy tests of the 1920s, and its action is described on its US prescribing information as virtually identical to that of LH. Vistara Labs supplies it as an HCG 5,000 IU lyophilised vial.
Findings
- HCG is built from two subunits: an alpha subunit of 93 amino acids shared with LH, FSH and TSH, and a beta subunit of 145 amino acids unique to HCG.
- Eight carbohydrate side chains make up about 30% of its molecular weight (2017).
- It binds the LH/choriogonadotropin receptor, stimulating testosterone production in the testes and progesterone production in the ovary.
- Early in pregnancy, blood levels double about every 1.5-2 days, which is why it became the basis of pregnancy testing (2017).
- After injection, purified HCG clears in two phases, with a slower phase of 24-33 hours (2017).
View product →What is HCG?
HCG is a polypeptide hormone produced by the human placenta, made of an alpha and a beta subunit (Novarel prescribing information, DailyMed). It is produced mainly by the syncytiotrophoblast, the outer layer of cells that forms the placenta’s contact with the mother’s blood. The alpha subunit has 93 amino acids (14.5 kDa) and the beta subunit 145 amino acids (22.2 kDa), and eight carbohydrate side chains account for about 30% of the molecule’s weight (Nwabuobi et al., Int J Mol Sci, 2017).
That makes HCG much larger and more complex than the short peptides in most research catalogues. It is often called the “HCG peptide”, and our HCG Peptide: What It Is, Why It Is Measured in IU, and Its Clinical History article explains the naming and the units in depth.
A family of related hormones
HCG belongs to the glycoprotein hormone family. Its alpha subunit is essentially identical to the alpha subunits of the pituitary hormones LH, follicle-stimulating hormone (FSH) and thyroid-stimulating hormone (TSH); the beta subunits differ and give each hormone its specific job (Novarel prescribing information). HCG also exists in several forms: regular HCG, sulfated HCG and hyperglycosylated HCG, which carries extra sugar chains (Nwabuobi et al., 2017).
Where it came from
HCG entered science through pregnancy testing. In 1927-1928, the German scientists Selmar Aschheim and Bernhard Zondek developed the first biological pregnancy test, which detected HCG in urine by its effect on the ovaries of immature mice or rats. Animal tests of this kind were used from the 1920s to the 1960s, before antibody-based tests replaced them; every modern pregnancy test still works by detecting HCG in urine or blood (Lis, Antibodies, 2023). Clinical HCG has long been extracted from pregnancy urine: the Novarel product, for example, is a water-soluble glycoprotein derived from human pregnancy urine and supplied as a lyophilised powder (Novarel prescribing information).
How HCG works
HCG binds the luteinising hormone/choriogonadotropin receptor (LHCGR), the same receptor that LH uses (Nwabuobi et al., 2017). Its prescribing information describes its action as virtually identical to that of pituitary LH, with a small degree of FSH activity as well (Novarel prescribing information). Through that receptor it:
- Stimulates the testes. HCG acts on Leydig cells, the testosterone-producing cells between the sperm-forming tubules, to make androgens.
- Stimulates the ovary. It acts on the corpus luteum, the structure left after ovulation, to make progesterone, and can substitute for the mid-cycle LH surge that triggers ovulation.
- Maintains early pregnancy. As LH falls in early pregnancy, placental HCG keeps the corpus luteum working, sustaining oestrogen and progesterone and preventing menstruation.
All three actions are set out in the US prescribing information (Novarel prescribing information). Because HCG acts directly on the gonads, it sits one step further down the hormone chain than kisspeptin, which works at the hypothalamus; the contrast is covered in Kisspeptin vs HCG and What Is Kisspeptin?
How long it stays in circulation
When purified HCG is injected, it clears in two phases: a rapid phase of about 5-6 hours and a slower phase of about 24-33 hours. Natural HCG after a full-term pregnancy clears in three phases, of about 3.6, 18 and 53 hours (Nwabuobi et al., 2017). Those figures are far longer than the minutes-long half-lives of many small peptides.
What the research has shown
A marker of pregnancy
The best-documented role of HCG is in early pregnancy. In IVF cycles, the beta subunit has been detected as early as the transfer of eight-cell embryos, two days after fertilisation, and in a viable pregnancy serum levels rise exponentially, doubling within about 1.5-2 days (Nwabuobi et al., 2017). That predictable rise is what makes HCG measurement useful for confirming and monitoring pregnancy.
A tumour marker
HCG is also used to diagnose and follow certain cancers. For gestational trophoblastic disease, a group of tumours arising from placental tissue, HCG is described as the most sensitive tumour marker available, and its hyperglycosylated form has been linked to the growth and invasion of placental and germ cell tumours (Nwabuobi et al., 2017). The same review lists uses ranging from diagnosing and monitoring pregnancy to cancer surveillance.
Approved clinical uses
HCG has a long record as a prescription medicine. The US prescribing information lists three indications: prepubertal cryptorchidism (undescended testes) not due to an anatomical blockage, selected cases of hypogonadotropic hypogonadism in males (low testosterone caused by a pituitary shortfall), and induction of ovulation in women whose anovulation is not due to primary ovarian failure (Novarel prescribing information). In cryptorchidism, the label notes that HCG may also help predict whether surgery will be needed later. How HCG compares with clomiphene, a drug that acts higher in the hormone chain, is covered in HCG vs Clomid.
HCG at a glance
| Question | Answer |
|---|---|
| Type | Glycoprotein hormone, two subunits |
| Made by | Placenta (syncytiotrophoblast) |
| Receptor | LH/choriogonadotropin receptor |
| Clearance | Two phases after injection; slow phase 24-33 h |
| Measured in | International units of activity |
Forms Vistara Labs stocks
HCG comes as a 5,000 IU lyophilised vial. Like other gonadotropins it is labelled in units of biological activity rather than milligrams. The concentration arithmetic is in how much bacteriostatic water for an HCG 5000 IU vial, certificates of analysis are on the lab reports page, and ordering details are in Buy HCG in Canada.
HCG is supplied by Vistara Labs for laboratory research use only. The clinical history above is described as published fact, not as guidance.
Frequently asked questions
What is HCG?
HCG, or human chorionic gonadotropin, is a glycoprotein hormone made by the placenta. It has an alpha subunit shared with LH, FSH and TSH and a unique beta subunit, and it acts through the same receptor as luteinising hormone.
What does HCG do in the body?
In early pregnancy it keeps the corpus luteum producing progesterone and oestrogen after LH falls. Through the LH receptor it also stimulates testosterone production by Leydig cells in the testes and progesterone production in the ovary.
Is HCG a peptide?
Strictly, HCG is a glycoprotein: two protein subunits of 93 and 145 amino acids with eight sugar chains making up about 30% of its weight. It is often called the HCG peptide, but it is much larger than most research peptides.
Why is HCG measured in IU?
HCG is labelled by its biological activity in units rather than by weight, as the US prescribing information does with USP Units. Our clinical history article explains the background to the units in detail.
What has research shown about HCG?
Research established HCG as the hormone that maintains early pregnancy, the basis of every modern pregnancy test since the Aschheim-Zondek test of 1927-1928, the most sensitive marker for gestational trophoblastic disease, and an approved medicine with three listed indications in the United States.
Product details from vistaralabs.ca, October 2026. Sources: Nwabuobi C et al. hCG: biological functions and clinical applications. Int J Mol Sci. 2017. PMID 28937611. Novarel (chorionic gonadotropin for injection) prescribing information, DailyMed. Lis K. From cereal grains to immunochemistry: what role have antibodies played in the history of the home pregnancy test. Antibodies. 2023. PMID 37753970.
More on this: Hormonal, Growth Hormone & Body Composition Research.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
References
hCG has an extensive controlled human research literature; it is a glycoprotein hormone rather than a short research peptide.
- Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppressionRandomised trial; 29 normal men on testosterone enanthate randomised to placebo or varying hCG doses.
- A double-blind, placebo-controlled, randomized clinical trial of recombinant human chorionic gonadotropin on muscle strength and physical function and activity in older men with partial age-related androgen deficiencyDouble-blind, placebo-controlled randomised trial in older men with partial age-related androgen deficiency.
Links open the study record on PubMed so the source can be checked directly. Listing a study is not a claim that its findings apply to any other use, product or route of administration. Research use only.
