Overview
Human chorionic gonadotropin (HCG) is a naturally occurring glycoprotein hormone produced by the placenta during pregnancy. Structurally, HCG consists of an α-subunit (identical to LH, FSH, and TSH) and a unique β-subunit that confers its specific biological activity. With a molecular weight of approximately 36,700 Da, HCG is one of the largest peptide/protein therapeutics in clinical use.
HCG's primary biological function is to maintain the corpus luteum during early pregnancy, ensuring continued progesterone production until the placenta assumes steroidogenic function around week 8–10. In therapeutic applications, HCG mimics luteinizing hormone (LH) due to their shared α-subunit and similar receptor binding, making it invaluable for fertility treatment in both sexes.
In men, HCG stimulates Leydig cells to produce testosterone and maintains spermatogenesis, making it an essential adjunct to testosterone replacement therapy (TRT) where endogenous gonadotropin suppression would otherwise cause testicular atrophy and infertility. In women, HCG is used as an ovulation trigger in assisted reproduction protocols.
HCG's use in 'HCG diet' protocols (combining HCG with very-low-calorie diets) has been widely discredited. Multiple controlled studies and meta-analyses found no benefit of HCG over placebo for weight loss, and the FDA has issued warnings against homeopathic HCG weight loss products.
Quick facts
- Mechanism
- LH-mimetic glycoprotein stimulating gonadal steroidogenesis
- Primary use
- Fertility Treatment & Testosterone Support
- Evidence
- high
- FDA
- Approved
- Route
- Intramuscular or subcutaneous injection
- Typical results
- Fertility: ovulation induction within 24–48 hours; TRT support: maintained testicular function within 2–4 weeks
Chemical information
HCG (Glycoprotein) is a hormonal compound with a molecular weight of ~36,700 Da. Its structural characteristics underpin its biological activity in hormonal signaling and endocrine function.
How HCG works
HCG binds to the luteinizing hormone/choriogonadotropin receptor (LHCGR), a G protein-coupled receptor expressed on Leydig cells (testes), granulosa/theca cells (ovaries), and corpus luteum. Receptor binding activates adenylyl cyclase → cAMP → PKA signaling, which upregulates StAR protein (steroidogenic acute regulatory protein) to facilitate cholesterol transport into mitochondria, the rate-limiting step in steroid hormone biosynthesis.
In Leydig cells, LHCGR activation by HCG stimulates the entire steroidogenic cascade: cholesterol → pregnenolone → progesterone → 17α-hydroxyprogesterone → androstenedione → testosterone. HCG's longer half-life compared to endogenous LH (24–36 hours vs. 20 minutes) provides more sustained stimulation, enabling twice-weekly or even weekly dosing protocols for TRT support.
In women undergoing assisted reproduction, HCG administration triggers the final maturation of ovarian follicles (mimicking the natural LH surge) and induces ovulation approximately 36 hours after injection. This predictable timing allows precise scheduling of intrauterine insemination or oocyte retrieval for IVF. HCG also supports the luteal phase by maintaining progesterone production from the corpus luteum.
During TRT, exogenous testosterone suppresses hypothalamic GnRH and pituitary LH/FSH secretion through negative feedback, leading to testicular atrophy and azoospermia. HCG provides direct Leydig cell stimulation independent of the HPG axis, maintaining intratesticular testosterone (ITT) levels at 50–80% of baseline even during TRT, preserving testicular size and residual spermatogenesis.
- LHCGR activation: Binds LH/CG receptor with high affinity on gonadal cells
- StAR protein upregulation: Increases mitochondrial cholesterol transport for steroidogenesis
- Testosterone production: Directly stimulates Leydig cell testosterone synthesis
- Ovulation induction: Triggers final follicular maturation and oocyte release
- Testicular maintenance: Preserves testicular volume and spermatogenesis during TRT
Pharmacokinetics
| Parameter | Value | Significance |
|---|---|---|
| Molecular Weight | ~36,700 Da | Large glycoprotein; not orally bioavailable |
| Half-life | 24–36 hours | Much longer than LH (~20 min), enabling twice-weekly dosing |
| Peak Levels | 6–12 hours post-injection | Gradual absorption from injection site |
| Duration of Effect | 5–7 days | Steroidogenic effects persist beyond plasma elimination |
Dosing & administration
HCG dosing varies by indication and individual factors. Refer to the official prescribing information for approved indications.
Any use should be conducted under qualified medical supervision with appropriate monitoring of safety markers.
Side effects & safety
Safety data for HCG is established for approved indications via clinical trials. Long-term effects in humans remain incompletely characterized.
Common
- • FDA-approved for fertility treatment in both men and women
- • Maintains testicular function during testosterone replacement therapy
- • Preserves spermatogenesis and fertility potential during TRT
- • Predictable ovulation induction for IVF timing
- • Long clinical track record with well-characterized safety profile
- • Available in recombinant (Ovidrel) and urinary-derived (Pregnyl) forms
Serious / potential risks
- • Ovarian hyperstimulation syndrome (OHSS) in women
- • Headache and irritability
- • Gynecomastia from elevated estradiol (via aromatization)
- • Injection site pain and swelling
- • Water retention and bloating
- • Multiple pregnancy risk when used for ovulation induction
Drug interactions
| Medication | Interaction | Recommendation |
|---|---|---|
| Testosterone (TRT) | Synergistic/complementary | Standard combination; HCG preserves testicular function during TRT |
| Aromatase inhibitors (Anastrozole) | Reduces HCG-induced estradiol | Often co-prescribed to manage estrogen from HCG-stimulated testosterone |
| Clomiphene citrate | Alternative HPG axis approach | Different mechanism (SERM vs direct LH mimetic); generally not combined |
| GnRH agonists (Lupron) | Opposing effects | GnRH agonists suppress gonadotropins; HCG bypasses this suppression |
Storage & handling
Lyophilized (powder)
- • Store at -20°C to 4°C (freezer or refrigerator)
- • Protect from light and moisture
- • Stable for 12–24 months when stored properly
- • Keep in original sealed container until reconstitution
Reconstituted solution
- • Refrigerate at 2–8°C after reconstitution
- • Use bacteriostatic water for multi-dose reconstitution
- • Typical stability: 14–28 days refrigerated
- • Do not freeze reconstituted solution
Cost & availability
| Source | Cost | Notes |
|---|---|---|
| Research suppliers | Varies widely | Quality and purity vary significantly between sources |
| Compounding pharmacies | Prescription required | Higher quality assurance and purity testing |
The bottom line
HCG is a hormonal compound with research interest in fertility, testosterone, lh mimetic. While preclinical evidence is encouraging, it has received FDA approval for specific indications. Any use should be under qualified medical supervision.
Best for
- • Researchers studying hormonal signaling and endocrine function
- • Individuals interested in fertility under medical guidance
Not for
- • Self-administration without medical supervision
- • Pregnant or breastfeeding individuals
- • Individuals with contraindicated conditions
Related compounds
Frequently asked questions
References
- [1] Coviello AD, Matsumoto AM, Bremner WJ, et al.. Low-dose human chorionic gonadotropin maintains intratesticular testosterone in normal men with testosterone-induced gonadotropin suppression. J Clin Endocrinol Metab (2005). doi: 10.1210/jc.2004-0802 PMID: 15562016
- [2] Katz DJ, Nabulsi O, Tal R, Mulhall JP.. Outcomes of clomiphene citrate treatment in young hypogonadal men. BJU Int (2012). doi: 10.1111/j.1464-410X.2011.10702.x PMID: 22085203
- [3] Lijesen GK, Theeuwen I, Assendelft WJ, Van Der Wal G.. The effect of human chorionic gonadotropin (HCG) in the treatment of obesity. Br J Clin Pharmacol (1995). doi: 10.1111/j.1365-2125.1995.tb04535.x PMID: 8562309
- [4] Stenman UH, Tiitinen A, Alfthan H, Valmu L.. The classification, functions and clinical use of different isoforms of HCG. Hum Reprod Update (2006). doi: 10.1093/humupd/dml029 PMID: 16775193