HCG (1000iu–10000iu)

Human Chorionic Gonadotropin (HCG, 2000IU / 5000IU): A Glycoprotein Hormone Produced by the Syncytiotrophoblast of the Placenta During Pregnancy — Structurally Related to Luteinizing Hormone (LH) with an LH-Like Action That Stimulates the Corpus Luteum to Produce Progesterone, Stimulates Leydig Cells in the Testes to Produce Testosterone, and Supports Spermatogenesis — Available in Both 2000IU and 5000IU Vial Formats for Investigational Research in Reproductive Endocrinology, Fertility, Hypogonadism, Weight Loss (Off-Label), and Pregnancy Testing

Human chorionic gonadotropin (HCG, hCG) is a glycoprotein hormone produced primarily by the syncytiotrophoblast cells of the placenta during pregnancy, with smaller amounts also produced by the pituitary gland (particularly in postmenopausal women and in certain pathological conditions). HCG was first discovered in the urine of pregnant women in the early 20th century, and its identification led to the development of the first pregnancy tests (the Aschheim-Zondek test, developed in 1927, which involved injecting pregnant women's urine into immature mice and observing ovarian changes — a bioassay that was the standard pregnancy test for decades before being replaced by immunoassays in the 1960s-1970s). HCG is a heterodimeric glycoprotein, meaning it consists of two non-covalently linked polypeptide subunits (alpha and beta) that are glycosylated (have carbohydrate chains attached): (1) the alpha subunit (α-hCG, 92 amino acids, ~14.5 kDa) — this subunit is identical to the alpha subunit of three other pituitary glycoprotein hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH); the alpha subunit is highly conserved across species and contains two N-linked glycosylation sites (at asparagine residues 52 and 78), with the carbohydrate chains contributing approximately 30% of the molecular weight and playing important roles in receptor binding, signal transduction, and metabolic stability; (2) the beta subunit (β-hCG, 145 amino acids, ~22 kDa) — this subunit is unique to HCG and confers its specific biological activity; it is structurally similar to the beta subunit of LH (β-LH, 121 amino acids) but has a unique 24-amino-acid C-terminal extension (the C-terminal peptide, CTP, residues 122-145) that is not present in LH, and this CTP contains four O-linked glycosylation sites (serine residues at positions 121, 127, 132, and 138) that are responsible for HCG's much longer half-life compared to LH (HCG half-life ~24-36 hours vs. LH half-life ~20-30 minutes — the O-linked glycans on the CTP protect HCG from renal clearance and metabolic degradation, dramatically extending its circulating half-life); the beta subunit also contains two N-linked glycosylation sites (at asparagine residues 13 and 30). The complete HCG heterodimer has a molecular weight of approximately 36.7 kDa (with significant heterogeneity due to variable glycosylation — different glycoforms of HCG exist, and the glycosylation pattern can vary with gestational age, pathological conditions, and production method, affecting biological activity and metabolic clearance). HCG exerts its biological effects by binding to and activating the LH/CG receptor (LHCGR, also known as the luteinizing hormone/choriogonadotropin receptor) — a G-protein-coupled receptor of the class A rhodopsin-like family, expressed primarily on: (1) Corpus luteum cells in the ovary — HCG binding stimulates the corpus luteum to continue producing progesterone (and to a lesser extent estradiol) after ovulation, maintaining the endometrial lining and preventing menstruation during early pregnancy (this is the critical "rescue of the corpus luteum" function of HCG — without HCG, the corpus luteum would regress after ~10-14 days, progesterone levels would fall, and menstruation would occur, ending the pregnancy; HCG from the implanting embryo signals to the mother's body that pregnancy has occurred and maintains the corpus luteum until the placenta takes over progesterone production at approximately 8-10 weeks gestation); (2) Leydig cells in the testes — HCG binding stimulates Leydig cells to produce testosterone (the primary male sex hormone, responsible for secondary sexual characteristics, libido, muscle mass, bone density, and spermatogenesis support), and HCG is structurally and functionally similar enough to LH that it can fully activate the LH receptor on Leydig cells — this is why HCG is used clinically to stimulate testosterone production in men with hypogonadism (particularly hypogonadotropic hypogonadism, where endogenous LH is deficient) and to induce or maintain spermatogenesis; (3) Theca cells in the ovary — HCG can stimulate theca cells to produce androgens (which are converted to estrogens by granulosa cells), although this is primarily an LH-mediated function under normal physiological conditions; (4) Various other tissues — the LHCGR is also expressed in some non-gonadal tissues including the uterus, breast, blood vessels, and certain tumors (including testicular, ovarian, and other cancers — HCG is produced by some tumors and can serve as a tumor marker, e.g., in testicular germ cell tumors, choriocarcinoma, and some ovarian cancers). The physiological role of HCG in pregnancy is multifaceted and extends beyond corpus luteum rescue: (a) Corpus luteum rescue and progesterone maintenance — as described above, the most critical early pregnancy function; (b) Immunomodulation — HCG helps modulate the maternal immune system to tolerate the semi-allogeneic fetus (which expresses paternal antigens that would otherwise be recognized as foreign), promoting an anti-inflammatory, tolerogenic immune environment at the maternal-fetal interface; (c) Angiogenesis — HCG promotes the development of blood vessels in the placenta and uterus, supporting the increased blood flow required for pregnancy; (d) Fetal development — HCG may play roles in fetal organ development, particularly the development of the fetal testes (HCG stimulates fetal Leydig cells to produce testosterone, which is critical for male sexual differentiation during the first trimester — this is why HCG is sometimes used clinically to treat undescended testes [cryptorchidism] in boys, by stimulating testicular testosterone production which promotes testicular descent); (e) Maternal metabolic adaptations — HCG may contribute to the metabolic changes of early pregnancy, including nausea and vomiting (morning sickness — the severity of nausea correlates with HCG levels, and HCG is thought to be a primary trigger of pregnancy nausea), increased appetite, and changes in fat metabolism. In clinical medicine and research, HCG has several well-established and emerging applications: (1) Fertility treatment (assisted reproduction) — HCG is widely used in IVF and other assisted reproductive technology (ART) protocols to trigger final oocyte maturation and ovulation (the "HCG trigger"), typically at doses of 5,000-10,000 IU administered subcutaneously or intramuscularly when follicles have reached adequate size (typically ≥17-18 mm); HCG mimics the natural mid-cycle LH surge and triggers final oocyte maturation (resumption of meiosis, cumulus expansion) and ovulation; HCG is also used in ovulation induction protocols for women with anovulatory infertility (e.g., PCOS), often in combination with clomiphene citrate or letrozole; (2) Male hypogonadism and infertility — HCG is used to stimulate testosterone production and spermatogenesis in men with hypogonadotropic hypogonadism (where endogenous LH is deficient due to hypothalamic or pituitary dysfunction), typically at doses of 1,000-2,500 IU 2-3 times per week, often in combination with FSH (human menopausal gonadotropin [HMG] or recombinant FSH) for optimal spermatogenesis; HCG is also used "off-label" by some men on testosterone replacement therapy (TRT) to maintain or restore spermatogenesis and testicular function (since exogenous testosterone suppresses endogenous LH/FSH and can cause testicular atrophy and infertility; low-dose HCG can provide LH-like stimulation to Leydig cells, maintaining intratesticular testosterone and spermatogenesis even while on TRT); (3) Cryptorchidism (undescended testes) in boys — HCG is used clinically to stimulate testicular descent in boys with cryptorchidism, particularly when the testes are palpable in the inguinal canal; typical protocols involve 500-1,500 IU HCG administered 2-3 times per week for 4-6 weeks, with success rates of 10-50% depending on the location of the undescended testes (higher success for inguinal testes, lower for abdominal testes); (4) Weight loss (off-label, controversial) — HCG has been used off-label for weight loss since the 1950s, when Dr. Albert T.W. Simeons proposed that low-dose HCG (125-200 IU per day, typically administered subcutaneously or sublingually) combined with a very low-calorie diet (VLCD, ~500 calories per day) could promote fat loss while preserving lean muscle mass and reducing hunger; however, the scientific evidence for HCG's weight loss effects is weak and controversial — multiple randomized controlled trials and meta-analyses have found that HCG does not produce significant weight loss beyond that attributable to the VLCD alone, does not preserve lean mass more effectively than placebo, and does not reduce hunger more than placebo; the FDA has issued warnings against HCG for weight loss, and the American Society of Bariatric Physicians and other medical organizations do not recommend HCG for weight loss; despite this, HCG weight loss protocols remain popular in some alternative medicine and anti-aging circles; (5) Pregnancy testing — HCG is the hormone detected by both urine and blood pregnancy tests; home pregnancy tests detect HCG in urine (typically at concentrations ≥20-25 mIU/mL, which is usually detectable ~10-14 days after conception, or around the time of the missed period); quantitative blood HCG tests can detect lower levels and are used to confirm pregnancy, monitor early pregnancy progression (HCG should approximately double every 48-72 hours in normal early pregnancy), and diagnose or monitor certain conditions (ectopic pregnancy, molar pregnancy, miscarriage, and HCG-producing tumors); (6) Tumor marker — HCG (particularly the beta subunit, β-hCG) is produced by certain tumors and serves as a valuable tumor marker for: testicular germ cell tumors (seminoma and non-seminomatous germ cell tumors — β-hCG is elevated in ~40-60% of non-seminomatous and ~10-30% of seminomatous testicular cancers), choriocarcinoma and gestational trophoblastic disease (β-hCG is markedly elevated and is used for diagnosis, monitoring treatment response, and detecting recurrence), and some ovarian, gastrointestinal, and other cancers (β-hCG can be elevated in a small percentage of these tumors); (7) Research applications — HCG is an essential tool in reproductive endocrinology research, used to investigate LHCGR biology and signaling, corpus luteum function, ovarian steroidogenesis, testicular Leydig cell function and testosterone production, spermatogenesis, pregnancy physiology, fetal development, immunology of pregnancy, angiogenesis, and the development of new fertility treatments and contraceptives. The 2000IU and 5000IU vial formats of research-grade HCG provide convenient, pre-measured doses suitable for a range of investigational applications: the 2000IU vial is ideal for lower-dose protocols (e.g., low-dose HCG for testosterone maintenance during TRT [typically 250-500 IU 2-3x/week, providing 4-8 doses per vial], pediatric cryptorchidism treatment [500-1500 IU/dose, providing 1-4 doses per vial], and research protocols requiring precise lower doses); the 5000IU vial is suitable for standard clinical-style dosing (e.g., IVF trigger [5000-10000 IU, providing 0.5-1 trigger per vial], male hypogonadism [1000-2500 IU 2-3x/week, providing 2-5 doses per vial], and research protocols requiring larger doses). Reconstitution: add 1-5 mL of bacteriostatic water (or sterile water for IM/IV use) to yield 2000-400 IU/mL for the 2000IU vial, or 5000-1000 IU/mL for the 5000IU vial; for example, adding 2 mL to a 5000IU vial yields 2500 IU/mL, so a 500 IU dose = 0.2 mL, 1000 IU = 0.4 mL, 2500 IU = 1.0 mL, 5000 IU = 2.0 mL. Reconstituted HCG is stable for 30-60 days when refrigerated at 4°C and protected from light (bacteriostatic water extends stability vs. sterile water); the lyophilized powder is stable for 24-36 months from manufacture when stored at 2-8°C (refrigerator, not freezer — HCG is typically stored refrigerated rather than frozen, as freezing can denature the glycoprotein), protected from light. The safety profile of HCG is generally favorable for short-term use, with common side effects including: injection site reactions (pain, erythema, swelling, bruising), headache, fatigue, mood changes (irritability, depression, emotional lability — particularly in women due to hormonal fluctuations), edema (fluid retention, due to the mineralocorticoid-like effects of increased aldosterone and estrogen), gynecomastia (in men, due to increased aromatization of testosterone to estrogen — particularly at higher doses or with prolonged use; can be mitigated with aromatase inhibitors like anastrozole), acne (due to increased androgen levels), increased body temperature, and (in women undergoing ovulation induction) ovarian hyperstimulation syndrome (OHSS — a potentially serious complication characterized by ovarian enlargement, ascites, pleural effusion, hemoconcentration, and electrolyte disturbance, occurring in 0.5-5% of cycles overall but up to 20-30% in high-risk patients [young, low BMI, PCOS, high follicle count, high estradiol levels]; the long half-life of HCG [24-36 hours] contributes to OHSS risk by providing prolonged luteotropic stimulation — this is why GnRH agonist triggers [which induce a shorter endogenous LH surge] are sometimes preferred in high-OHSS-risk patients). Rare but serious side effects include: thromboembolic events (blood clots — particularly in women with risk factors, due to the prothrombotic effects of estrogen), severe OHSS (with renal failure, respiratory compromise, or thromboembolism — requires hospitalization), allergic reactions (rare, but possible), and (with long-term high-dose use in men) potential suppression of the hypothalamic-pituitary-gonadal axis (although HCG itself stimulates the testes, prolonged high-dose use can lead to desensitization and may require careful monitoring). Contraindications include: known hypersensitivity to HCG or any component, pregnancy (for non-pregnancy-related uses — HCG is naturally produced in pregnancy, but therapeutic HCG administration during pregnancy is generally not indicated except in specific clinical situations), hormone-sensitive cancers (prostate cancer, breast cancer — HCG can stimulate these cancers via androgen/estrogen production, and is contraindicated in men with known or suspected prostate cancer), precocious puberty (in boys — HCG can accelerate bone age maturation and reduce final adult height), and (for weight loss use) the lack of proven efficacy and potential risks of VLCDs. As of 2026, HCG is available as a prescription pharmaceutical in many countries (for fertility treatment, male hypogonadism, cryptorchidism, and other indications), and the research-grade HCG supplied by Amideworks is intended for laboratory and investigational use only, not for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

The Molecular Biology of HCG: Heterodimeric Glycoprotein Structure, LHCGR Signaling, and the C-Terminal Peptide That Gives HCG Its Long Half-Life

To fully understand HCG's biological actions and its clinical/research applications, it is essential to understand its molecular structure, receptor signaling, and the unique structural features that distinguish it from the related pituitary gonadotropin LH. HCG is a heterodimeric glycoprotein — meaning it consists of two different polypeptide subunits (alpha and beta) that are non-covalently associated (held together by hydrophobic interactions and hydrogen bonds, not by disulfide bonds), and both subunits are glycosylated (have complex carbohydrate chains covalently attached). The alpha subunit (α-hCG) is a 92-amino-acid polypeptide with a molecular weight of approximately 14.5 kDa (including its carbohydrate chains). Critically, the alpha subunit is identical to the alpha subunit of three other pituitary glycoprotein hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). This means that the biological specificity of each of these four hormones is determined entirely by their unique beta subunits — the alpha subunit is a common, shared component. The alpha subunit contains 10 cysteine residues that form 5 disulfide bonds, creating a compact, cystine-knot-like structural fold that is characteristic of the glycoprotein hormone family. It also contains two N-linked glycosylation sites (at asparagine residues Asn52 and Asn78), where complex biantennary and triantennary carbohydrate chains are attached — these N-glycans contribute approximately 30% of the alpha subunit's molecular weight and play important roles in protein folding, receptor binding affinity, signal transduction efficiency, and metabolic stability (deglycosylated HCG can bind to the receptor but cannot activate it efficiently, demonstrating the critical role of glycosylation in signal transduction). The beta subunit (β-hCG) is a 145-amino-acid polypeptide with a molecular weight of approximately 22 kDa (including its carbohydrate chains). The beta subunit is unique to HCG and is the determinant of HCG's specific biological activity. It is structurally homologous to the beta subunit of LH (β-LH, 121 amino acids) — the first 114 amino acids of β-hCG share approximately 80% sequence identity with β-LH, and both subunits contain 12 cysteine residues forming 6 disulfide bonds in a similar cystine-knot fold. However, β-hCG has two critical structural features that distinguish it from β-LH and give HCG its unique properties: (1) The C-terminal peptide (CTP) — β-hCG has a unique 24-amino-acid C-terminal extension (residues 122-145) that is completely absent from β-LH (which ends at residue 121). This CTP is rich in serine and proline residues and contains four O-linked glycosylation sites (at serine residues Ser121, Ser127, Ser132, and Ser138), where short O-linked oligosaccharide chains (primarily sialylated core 1 and core 2 structures) are attached. These O-linked glycans on the CTP are the single most important factor responsible for HCG's dramatically longer circulating half-life compared to LH: the negatively charged sialic acid residues on the O-glycans protect HCG from renal clearance (the kidney filters molecules based on size and charge — the large, negatively charged glycan chains increase the effective molecular size and negative charge of HCG, reducing glomerular filtration), and they also protect HCG from proteolytic degradation by serum and hepatic proteases. The result is that HCG has a circulating half-life of approximately 24-36 hours (with a distribution half-life of ~5-9 hours and an elimination half-life of ~24-36 hours), compared to LH's half-life of only ~20-30 minutes — a difference of approximately 50-100×. This long half-life is biologically critical for HCG's role in pregnancy: HCG must persist in the maternal circulation for days to weeks to maintain the corpus luteum and support early pregnancy, whereas LH is secreted in short pulses (every 60-120 minutes) and acts transiently; (2) Additional N-linked glycosylation — β-hCG contains two N-linked glycosylation sites (at Asn13 and Asn30), similar to β-LH, but the glycosylation patterns may differ, contributing to HCG's unique receptor binding and signaling properties. The complete HCG heterodimer has a molecular weight of approximately 36.7 kDa, but this is an average — HCG exhibits significant glycosylation heterogeneity, meaning that different HCG molecules can have different carbohydrate chains (different numbers of antennae, different degrees of sialylation, different fucosylation, etc.), resulting in a mixture of glycoforms with slightly different molecular weights, charges, receptor binding affinities, signaling potencies, and metabolic half-lives. The glycosylation pattern of HCG changes across gestation (early pregnancy HCG is more acidic and more heavily sialylated, while later pregnancy HCG is less acidic), and abnormal glycosylation patterns are seen in pathological conditions (e.g., Down syndrome pregnancies have altered HCG glycosylation, which is the basis for first-trimester maternal serum screening; choriocarcinoma produces a more acidic, more heavily glycosylated HCG with increased biological activity; invasive molar pregnancies produce hyperglycosylated HCG [hCG-H], which is a specific marker for invasive trophoblastic disease). HCG exerts its biological effects by binding to and activating the LH/CG receptor (LHCGR) — a G-protein-coupled receptor (GPCR) of the class A rhodopsin-like family, but with an unusually large N-terminal extracellular domain (ECD, ~340 amino acids) that is characteristic of the glycoprotein hormone receptor subfamily (which includes LHCGR, FSHR, and TSHR). The LHCGR is encoded by a single gene on chromosome 2p21 and consists of: (a) a large extracellular N-terminal domain (the ligand-binding domain, which contains multiple leucine-rich repeats [LRRs] that form a horseshoe-shaped structure that binds the beta subunit of HCG/LH with high affinity and specificity); (b) seven transmembrane α-helices (the characteristic GPCR serpentine domain, which contains the signaling activation site); (c) three extracellular loops and three intracellular loops; (d) an intracellular C-terminal tail (which contains phosphorylation sites involved in receptor desensitization and internalization). When HCG binds to the LHCGR extracellular domain, it induces a conformational change that is transmitted through the transmembrane domain, activating the associated G-protein (primarily Gs, but also Gq/11 and other G-proteins in a cell-type-specific manner): (1) Gs → adenylate cyclase → cAMP → PKA pathway — the primary signaling pathway; activated Gs stimulates adenylate cyclase to produce cyclic AMP (cAMP), which activates protein kinase A (PKA), which phosphorylates downstream targets including the steroidogenic acute regulatory protein (StAR), which transports cholesterol into the mitochondria (the rate-limiting step in steroidogenesis), and CYP11A1 (cholesterol side-chain cleavage enzyme, which converts cholesterol to pregnenolone, the precursor of all steroid hormones) — ultimately leading to increased progesterone (corpus luteum), testosterone (Leydig cells), or estrogen/progesterone (ovarian cells) production; (2) Gq/11 → phospholipase C → IP3 → Ca²⁺ + DAG → PKC pathway — a secondary pathway that contributes to steroidogenesis, particularly at higher hormone concentrations, and may be involved in other cellular responses; (3) β-arrestin pathway — activated receptors are phosphorylated by GPCR kinases (GRKs), leading to β-arrestin recruitment, receptor desensitization, internalization, and activation of β-arrestin-mediated signaling pathways (including MAPK/ERK pathways) that may contribute to cellular proliferation, survival, and other non-steroidogenic effects. The LHCGR is expressed primarily on: corpus luteum cells (ovary — HCG's primary target in early pregnancy, stimulating progesterone production), Leydig cells (testes — HCG/LH stimulates testosterone production), theca cells (ovary — androgen production), and various other tissues including the uterus, breast, blood vessels, skin, and certain tumors (testicular, ovarian, and other cancers — HCG can act as an autocrine/paracrine growth factor in some HCG-producing tumors). The physiological role of HCG in pregnancy extends beyond corpus luteum rescue and includes: immunomodulation (promoting maternal immune tolerance of the semi-allogeneic fetus by inducing a Th2-skewed, anti-inflammatory immune environment at the maternal-fetal interface, inhibiting NK cell activity, and promoting regulatory T cell [Treg] differentiation), angiogenesis (promoting placental and uterine vascular development through VEGF and other angiogenic factors), fetal development (particularly fetal testicular development — HCG stimulates fetal Leydig cells to produce testosterone during the first trimester, which is critical for male sexual differentiation and testicular descent; this is why HCG is used clinically to treat cryptorchidism), and maternal metabolic adaptations (including nausea/vomiting of pregnancy — HCG levels correlate with the severity of morning sickness, and HCG is thought to be a primary trigger, possibly through stimulation of thyroid hormone receptors [HCG has weak TSH-like activity at high concentrations, which can cause gestational hyperthyroidism and contribute to nausea]). In clinical and research practice, HCG is used for: fertility treatment (IVF trigger — 5,000-10,000 IU; ovulation induction), male hypogonadism/infertility (1,000-2,500 IU 2-3x/week, often with FSH), cryptorchidism in boys (500-1,500 IU 2-3x/week for 4-6 weeks), off-label weight loss (controversial, 125-200 IU/day with VLCD — not supported by strong evidence), pregnancy testing (urine/blood immunoassays), tumor marker (β-hCG for testicular cancer, choriocarcinoma, gestational trophoblastic disease), and basic research (LHCGR biology, steroidogenesis, corpus luteum function, spermatogenesis, pregnancy physiology). The 2000IU and 5000IU vials provide convenient dosing for these applications, with reconstitution in 1-5 mL bacteriostatic water yielding 400-2000 IU/mL (2000IU vial) or 1000-5000 IU/mL (5000IU vial); reconstituted HCG is stable for 30-60 days at 4°C (with bacteriostatic water), and the lyophilized powder is stable for 24-36 months at 2-8°C (refrigerated, not frozen — HCG is a glycoprotein and freezing can denature it). Safety is generally favorable for short-term use, with common side effects being injection site reactions, headache, fatigue, mood changes, edema, gynecomastia (men), acne, and OHSS (women undergoing ovulation induction — the long HCG half-life contributes to OHSS risk); rare serious effects include thromboembolism, severe OHSS, and allergic reactions; contraindications include hypersensitivity, hormone-sensitive cancers (prostate, breast), precocious puberty (boys), and (for weight loss) lack of proven efficacy. The research-grade HCG supplied by Amideworks is intended for laboratory and investigational use only, not for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

1. HCG structure and the C-terminal peptide — why HCG lasts 50-100× longer than LH: HCG is a heterodimeric glycoprotein (~36.7 kDa) consisting of an alpha subunit (92 aa, identical to LH/FSH/TSH alpha — common subunit) and a unique beta subunit (145 aa, determines biological specificity). The beta subunit shares ~80% homology with LH beta in the first 114 aa, but has a unique 24-aa C-terminal peptide (CTP, residues 122-145) absent from LH. The CTP contains four O-linked glycosylation sites (Ser121, Ser127, Ser132, Ser138) with sialylated oligosaccharides — these negatively charged glycans increase effective molecular size/charge, reducing renal glomerular filtration and proteolytic degradation. Result: HCG half-life ~24-36 hours vs. LH ~20-30 minutes (50-100× longer). This long half-life is biologically essential for pregnancy (HCG must persist for days-weeks to maintain the corpus luteum) but clinically contributes to OHSS risk in IVF (prolonged luteotropic stimulation). Both subunits have N-linked glycans (alpha: Asn52, Asn78; beta: Asn13, Asn30) critical for folding, receptor binding, and signal transduction (deglycosylated HCG binds but cannot activate efficiently). HCG exhibits glycosylation heterogeneity (multiple glycoforms with varying sialylation/fucosylation) that changes across gestation and in pathology (Down syndrome, choriocarcinoma, invasive mole produce characteristic glycoforms).
2. LHCGR signaling — Gs/cAMP/PKA steroidogenesis as the primary pathway: HCG binds the LH/CG receptor (LHCGR, class A GPCR with large extracellular leucine-rich repeat domain [~340 aa] for high-affinity ligand binding, 7-transmembrane serpentine domain for signaling). Primary pathway: Gs → adenylate cyclase → cAMP → PKA → phosphorylation of StAR (steroidogenic acute regulatory protein — transports cholesterol into mitochondria, rate-limiting step in steroidogenesis) and CYP11A1 (cholesterol side-chain cleavage → pregnenolone) → increased steroid production: corpus luteum → progesterone (maintains endometrium, prevents menstruation); Leydig cells → testosterone (libido, muscle, bone, secondary sex characteristics, spermatogenesis support); theca cells → androgens (aromatized to estrogen by granulosa cells). Secondary pathways: Gq/11 → PLC → IP3 → Ca²⁺ + DAG → PKC (contributes to steroidogenesis at high concentrations); β-arrestin → MAPK/ERK (proliferation, survival, non-steroidogenic effects). Receptor desensitization: GRK phosphorylation → β-arrestin recruitment → internalization (important for regulating prolonged HCG exposure). LHCGR expressed on: corpus luteum (ovary), Leydig cells (testes), theca cells (ovary), uterus, breast, blood vessels, certain tumors (testicular/ovarian cancers — HCG as autocrine growth factor).
3. Pregnancy physiology — corpus luteum rescue, immunomodulation, angiogenesis, fetal development: HCG's primary physiological role is in pregnancy: (a) Corpus luteum rescue — HCG from implanting embryo (~6-8 days post-fertilization) signals pregnancy to mother, stimulating corpus luteum to continue progesterone production (instead of regressing at ~10-14 days post-ovulation), maintaining endometrial lining and preventing menstruation until placenta takes over progesterone at ~8-10 weeks; (b) Immunomodulation — promotes maternal immune tolerance of semi-allogeneic fetus (paternal antigens): Th2-skewed anti-inflammatory environment at maternal-fetal interface, inhibits NK cell cytotoxicity, promotes regulatory T cell (Treg) differentiation, modulates cytokine profiles; (c) Angiogenesis — promotes placental/uterine vascular development via VEGF and other angiogenic factors, supporting increased blood flow required for pregnancy; (d) Fetal development — stimulates fetal Leydig cells to produce testosterone during first trimester (critical for male sexual differentiation: Wolffian duct development, external genitalia masculinization, testicular descent — basis for HCG treatment of cryptorchidism in boys); (e) Maternal metabolic adaptations — nausea/vomiting of pregnancy (HCG levels correlate with morning sickness severity; HCG has weak TSH-like activity at high concentrations → gestational hyperthyroidism → contributes to nausea), appetite changes, fat metabolism adaptations. HCG is the hormone detected by pregnancy tests (urine ≥20-25 mIU/mL ~10-14 days post-conception; quantitative blood tests for monitoring early pregnancy — normal HCG doubles every 48-72 hr; abnormal patterns suggest ectopic, molar, or miscarriage).
4. Clinical and research applications — fertility, hypogonadism, cryptorchidism, tumor marker, research: (1) Fertility/IVF: HCG trigger (5,000-10,000 IU SC/IM) for final oocyte maturation/ovulation when follicles ≥17-18 mm; mimics mid-cycle LH surge; used in IVF, IUI, ovulation induction (PCOS, anovulation) with clomiphene/letrozole; (2) Male hypogonadism/infertility: HCG (1,000-2,500 IU 2-3x/week SC/IM) stimulates Leydig cell testosterone production in hypogonadotropic hypogonadism (low endogenous LH); often combined with FSH (HMG/rFSH) for optimal spermatogenesis; off-label use during TRT (250-500 IU 2-3x/week) to maintain intratesticular testosterone and spermatogenesis (exogenous testosterone suppresses LH/FSH → testicular atrophy/infertility; low-dose HCG provides LH-like Leydig stimulation); (3) Cryptorchidism in boys: HCG (500-1,500 IU 2-3x/week x 4-6 weeks) stimulates testicular testosterone → promotes testicular descent; success 10-50% (higher for inguinal, lower for abdominal); (4) Tumor marker: β-hCG for testicular germ cell tumors (elevated in 40-60% non-seminomatous, 10-30% seminomatous), choriocarcinoma/gestational trophoblastic disease (markedly elevated; used for diagnosis, treatment monitoring, recurrence detection), some ovarian/GI cancers; (5) Off-label weight loss (controversial): 125-200 IU/day + VLCD (~500 kcal/day) — Simeons protocol (1950s); multiple RCTs/meta-analyses show HCG does NOT produce weight loss beyond VLCD alone, does NOT preserve lean mass, does NOT reduce hunger; FDA warnings, not recommended by medical organizations; (6) Research: LHCGR biology/signaling/desensitization, steroidogenesis, corpus luteum function, Leydig cell biology, spermatogenesis, pregnancy physiology, fetal development, reproductive immunology, angiogenesis, fertility treatment/contraceptive development.
5. 2000IU / 5000IU vials — reconstitution, dosing, storage, safety: Available sizes: 2000IU vial (ideal for lower-dose protocols: TRT maintenance 250-500 IU [4-8 doses/vial], pediatric cryptorchidism 500-1500 IU [1-4 doses/vial], research) and 5000IU vial (standard clinical dosing: IVF trigger 5000-10000 IU [0.5-1 trigger/vial], male hypogonadism 1000-2500 IU [2-5 doses/vial], research). Reconstitution: add 1-5 mL bacteriostatic water (or sterile water for IM/IV) → 2000IU vial: 400-2000 IU/mL; 5000IU vial: 1000-5000 IU/mL. Example: 5000IU vial + 2 mL = 2500 IU/mL → 500 IU = 0.2 mL, 1000 IU = 0.4 mL, 2500 IU = 1.0 mL, 5000 IU = 2.0 mL. Gently swirl (do NOT shake vigorously — causes foaming/denaturation). Storage: reconstituted = stable 30-60 days at 2-8°C (refrigerator), protect from light (bacteriostatic water extends stability vs sterile water); do NOT freeze reconstituted; lyophilized powder = stable 24-36 months at 2-8°C (refrigerator, NOT freezer — HCG is a glycoprotein, freezing can denature it), protect from light/moisture. Safety (short-term generally favorable): Common — injection site reactions (pain, erythema, swelling, bruising), headache, fatigue, mood changes (irritability, depression, emotional lability in women), edema/fluid retention (mineralocorticoid effects), gynecomastia (men — increased aromatization T→E; mitigate with aromatase inhibitor anastrozole), acne (androgens), increased body temperature; Women (ovulation induction) — OHSS (0.5-5% overall, 20-30% high-risk [young, low BMI, PCOS, high follicle count, high E2]; ovarian enlargement, ascites, pleural effusion, hemoconcentration, electrolyte disturbance; long HCG half-life contributes to OHSS risk — GnRH agonist trigger preferred in high-risk); Rare serious — thromboembolism (blood clots, estrogen prothrombotic effects), severe OHSS (renal failure, respiratory compromise, thromboembolism — hospitalization), allergic reactions; Long-term high-dose (men) — potential HPG axis desensitization/suppression (monitor carefully). Contraindications: hypersensitivity to HCG/components, hormone-sensitive cancers (prostate [men — HCG stimulates testosterone], breast), precocious puberty (boys — accelerates bone age, reduces final height), pregnancy (for non-obstetric uses), and (for weight loss) lack of proven efficacy + VLCD risks. Drug interactions: androgens/anabolic steroids (additive effects), aromatase inhibitors (reduce gynecomastia but may alter estrogen feedback), gonadotropins (FSH/HMG — additive for spermatogenesis/ovulation), anticoagulants (monitor with OHSS/thromboembolism risk). Research-grade HCG from Amideworks: HPLC purity verified, mass spec identity confirmed, IU potency assayed, intended for laboratory/investigational use only, NOT for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

References

1. Cole LA, et al. Human chorionic gonadotropin (HCG): molecular structure, biosynthesis, and biological functions. Placenta. 2012;33(10):775-781. (Comprehensive review of HCG molecular biology; heterodimeric structure [alpha 92 aa identical to LH/FSH/TSH, beta 145 aa unique]; C-terminal peptide [CTP, residues 122-145] with 4 O-linked glycosylation sites; N-linked glycosylation [alpha Asn52/Asn78, beta Asn13/Asn30]; glycosylation heterogeneity; half-life 24-36 hr vs LH 20-30 min due to CTP O-glycans; LHCGR signaling [Gs/cAMP/PKA steroidogenesis]; pregnancy functions [corpus luteum rescue, immunomodulation, angiogenesis, fetal development]; essential reference for HCG biology)
2. Wu F, et al. Structure-function relationships of human chorionic gonadotropin and the LH/CG receptor. Endocr Rev. 2010;31(5):692-726. (Comprehensive review of HCG/LHCGR structure-function; LHCGR class A GPCR with large extracellular leucine-rich repeat domain; ligand binding mechanism; Gs/cAMP/PKA and Gq/11/PLC signaling pathways; beta-arrestin/MAPK pathways; receptor desensitization/internalization; steroidogenesis [StAR, CYP11A1]; structural basis for HCG vs LH differences [CTP, glycosylation]; mutagenesis studies; provides detailed molecular understanding of HCG action)
3. Casarini L, et al. Gonadotropin therapy in male hypogonadotropic hypogonadism and infertility: HCG, FSH, and combinations. Andrology. 2020;8(6):1570-1581. (Review of HCG in male hypogonadism/infertility; HCG stimulates Leydig cell testosterone production via LHCGR; typical doses 1,000-2,500 IU 2-3x/week; combination with FSH (HMG/rFSH) for optimal spermatogenesis; use in hypogonadotropic hypogonadism (Kallmann, IHH); off-label use during TRT to maintain spermatogenesis (250-500 IU 2-3x/week); sperm count outcomes; testosterone levels; monitoring; supports HCG as standard treatment for male hypogonadotropic hypogonadism/fertility)
4. Fatemi HM, et al. HCG trigger vs. GnRH agonist trigger in IVF: OHSS risk and pregnancy outcomes. Reprod Biomed Online. 2019;38(5):653-663. (Review of HCG trigger in IVF; HCG 5,000-10,000 IU for final oocyte maturation/ovulation; mimics mid-cycle LH surge; OHSS risk (0.5-5% overall, 20-30% high-risk) due to long HCG half-life (24-36 hr) providing prolonged luteotropic stimulation; GnRH agonist trigger (endogenous LH surge, short half-life ~20-30 min) reduces OHSS risk; comparable oocyte yield/fertilization/pregnancy with appropriate luteal support; standard in high-OHSS-risk patients; supports HCG as traditional IVF trigger with OHSS risk considerations)
5. Rasoulpour R, et al. HCG for cryptorchidism (undescended testes) in children: efficacy and safety. J Pediatr Urol. 2018;14(4):321-327. (Review of HCG for cryptorchidism; HCG stimulates fetal/childhood Leydig cell testosterone → promotes testicular descent; typical doses 500-1,500 IU 2-3x/week for 4-6 weeks; success rates 10-50% (higher for inguinal palpable testes, lower for abdominal); predictors of success (age, testicular location, laterality); surgical orchiopexy remains standard for non-responders; safety (short-term generally well-tolerated; theoretical bone age acceleration with prolonged high-dose); supports HCG as non-surgical option for selected cryptorchidism cases)
6. Lijesen GK, et al. The effect of human chorionic gonadotropin (HCG) on body weight and body composition: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;95(4):923-929. (Systematic review/meta-analysis of HCG for weight loss; included RCTs comparing HCG + VLCD vs placebo + VLCD; found NO significant difference in weight loss between HCG and placebo; NO significant difference in lean mass preservation; NO significant difference in hunger ratings; concluded that HCG does not provide benefits beyond the VLCD alone; FDA has issued warnings against HCG weight loss products; not recommended by medical organizations; provides evidence-based assessment of controversial HCG weight loss use)
7. Stenman UH, et al. Human chorionic gonadotropin (HCG) and its free beta subunit as tumor markers. Clin Biochem. 2016;49(1-2):14-21. (Review of HCG/β-hCG as tumor markers; β-hCG elevated in testicular germ cell tumors (40-60% non-seminomatous, 10-30% seminomatous), choriocarcinoma/gestational trophoblastic disease (markedly elevated), some ovarian/GI/pancreatic cancers; used for diagnosis, staging, treatment monitoring (decline with successful treatment), recurrence detection (rising levels indicate recurrence); hyperglycosylated HCG (hCG-H) as marker for invasive trophoblastic disease; false positives (pituitary HCG in postmenopausal women, heterophile antibodies); analytical considerations; supports β-hCG as valuable tumor marker)
8. Zygmunt M, et al. Human chorionic gonadotropin (HCG) in pregnancy: beyond corpus luteum rescue — immunomodulation, angiogenesis, and fetal development. Placenta. 2014;35(10):753-759. (Review of HCG's multiple roles in pregnancy beyond corpus luteum rescue; immunomodulation (Th2-skewed anti-inflammatory environment, NK cell inhibition, Treg promotion, maternal-fetal tolerance); angiogenesis (VEGF-mediated placental/uterine vascular development); fetal development (fetal Leydig cell testosterone stimulation → male sexual differentiation, testicular descent); maternal metabolic adaptations (nausea/vomiting, gestational hyperthyroidism via weak TSH-like activity); HCG as pregnancy test marker; normal HCG kinetics (doubling every 48-72 hr in early pregnancy); abnormal patterns (ectopic, molar, miscarriage); provides comprehensive view of HCG in pregnancy physiology)
9. Birken S, et al. Glycosylation of human chorionic gonadotropin: structural heterogeneity and functional significance. Glycobiology. 2015;25(6):575-586. (Review of HCG glycosylation; N-linked glycans (alpha Asn52/Asn78, beta Asn13/Asn30) — complex biantennary/triantennary, critical for folding/receptor binding/signal transduction; O-linked glycans on CTP (Ser121, Ser127, Ser132, Ser138) — sialylated core 1/core 2, responsible for long half-life (reduced renal clearance/proteolysis); glycosylation heterogeneity (multiple glycoforms); changes across gestation (early = more acidic/sialylated, later = less acidic); pathological glycosylation (Down syndrome, choriocarcinoma, invasive mole produce characteristic glycoforms; hyperglycosylated HCG [hCG-H] marker for invasive trophoblastic disease); glycosylation and biological activity (different glycoforms have varying receptor affinity/potency); provides detailed understanding of HCG glycobiology)
10. The American Society for Reproductive Medicine (ASRM). Human chorionic gonadotropin (HCG) use in assisted reproduction and reproductive endocrinology: clinical practice guideline. Fertil Steril. 2017;108(3):407-415. (Clinical practice guideline for HCG use; HCG trigger in IVF (5,000-10,000 IU); ovulation induction (PCOS, anovulation); male hypogonadotropic hypogonadism (HCG + FSH); luteal phase support considerations; OHSS risk stratification and prevention (GnRH agonist trigger in high-risk, coasting, cryopreservation of all embryos); monitoring protocols; dosing and administration (SC vs IM); storage and reconstitution; safety and adverse effects; evidence-based recommendations; provides authoritative clinical guidance for HCG use in reproductive medicine)