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Overview
What is HCG (Human Chorionic Gonadotropin)?
Human Chorionic Gonadotropin (HCG) is a glycoprotein hormone naturally produced by the placenta during pregnancy. It consists of two subunits: an alpha subunit identical to other pituitary hormones (LH, FSH, TSH) and a unique beta subunit that confers HCG's specific biological activity. Pharmaceutical HCG is derived from the urine of pregnant women or produced recombinantly. It binds to and activates LH receptors, making it valuable for treating hypogonadism, infertility, and cryptorchidism. In TRT protocols, HCG is commonly used to maintain testicular function, preserve fertility, and prevent testicular atrophy.
Key Benefits
Maintains testicular function during TRT, preserves fertility, prevents testicular atrophy, stimulates endogenous testosterone production, induces ovulation in women, treats cryptorchidism in children
Mechanism of Action
HCG binds to LH receptors on Leydig cells in the testes, stimulating testosterone and estrogen biosynthesis. In women, it acts on ovarian theca cells to stimulate progesterone production and triggers final oocyte maturation. Half-life is approximately 24-36 hours with peak levels 6-12 hours post-injection. Bioavailability is 40-50% via subcutaneous or intramuscular routes.
Molecular Information
Weight
36,700 Da (36.7 kDa)
Length
237 amino acids total (alpha: 92 aa + beta: 145 aa)
Type
Heterodimeric glycoprotein with two non-covalently linked subunits
Amino Acid Sequence:
Alpha subunit (92 aa): identical to LH, FSH, and TSH alpha subunits. Beta subunit (145 aa): unique to HCG with 24 aa C-terminal extension not found in LH. Heavy glycosylation (~30% carbohydrate content)
* Extensive N-linked and O-linked glycosylation. The glycan chains extend half-life and influence receptor binding. Urinary-derived (e.g., Pregnyl) vs recombinant (e.g., Ovidrel) forms differ in glycosylation patterns
Research Indications
Cryptorchidism (Undescended Testes)
FDA-approved for prepubertal cryptorchidism not due to anatomical obstruction. Dosing: 1000-5000 IU 2-3 times weekly for 3-4 weeks. Success rate ~25% as monotherapy
Hypogonadotropic Hypogonadism (Males)
FDA-approved for secondary hypogonadism to stimulate testosterone production. Often combined with FSH for spermatogenesis induction. Dosing: 1000-2000 IU 2-3 times weekly
Ovulation Induction (Females)
FDA-approved as trigger for final follicular maturation and ovulation in assisted reproduction. Single dose of 5000-10,000 IU (or 250 mcg recombinant) when lead follicle reaches 18-20mm
Research Protocols
Disclaimer
These are commonly discussed research protocols and not medical advice. Consult a healthcare provider before use.
Timing
Administer HCG 2-3 times weekly, evenly spaced. For TRT, many inject HCG on days between testosterone injections. Consistency of schedule is more important than specific timing.
Peptide Interactions
How to Reconstitute
Important
Always use bacteriostatic water (BAC). Sterile technique is essential.
Remove HCG vial and diluent from packaging
Clean the rubber stoppers of both vials with alcohol swabs
Draw the diluent (typically 1-2 mL provided) into syringe
Slowly inject diluent into HCG vial, aiming at the vial wall
Gently swirl to dissolve - do not shake vigorously
Allow to sit until completely dissolved and solution is clear
Calculate concentration: e.g., 5000 IU in 2 mL = 2500 IU/mL
Label vial with reconstitution date and concentration
Store reconstituted HCG in refrigerator at 2-8°C
Use within 30-60 days (depending on diluent and product)
Quality Indicators
White lyophilized powder
Should appear as white to off-white powder or cake in sealed vial
Clear, colorless reconstituted solution
After reconstitution with provided diluent, solution should be completely clear
Pharmaceutical-grade product with proper labeling
Brands: Pregnyl, Novarel (urinary), Ovidrel (recombinant). Should have clear expiration date and lot number
Proper cold chain for recombinant products
Recombinant HCG (Ovidrel) requires refrigeration throughout shipping and storage
Generic/compounding pharmacy products
Quality varies. Ensure compounding pharmacy is accredited and product is properly stored
Cloudy, discolored, or particles visible
Any turbidity, yellow/brown color, or floating particles indicates degradation
Vial seal compromised or product past expiration
Never use HCG if seal is broken or after expiration date
What to Expect
- Day 1-3: No immediate noticeable effects; HCG is working at cellular level
- Week 1-2: Testosterone increase detectable on labs; possible improved mood/energy if previously deficient
- Week 2-4: Testicular fullness/size improvement noticeable; improved sense of well-being
- Week 4-8: Stable testosterone levels; fertility parameters beginning to improve
- Month 2-3: Sperm count improvements if used for fertility; sustained testicular function
- Long-term: Maintained testicular size and function with ongoing use; fertility preserved
- Note: Effects depend heavily on context (TRT adjunct vs monotherapy vs fertility protocol)
Side Effects & Safety
- FDA-approved for specific indications - discuss off-label use with physician
- May cause or worsen gynecomastia due to increased estrogen - monitor and manage with AI if needed
- High doses can cause excessive testosterone and estrogen - start low, titrate based on labs
- Can cause headaches, irritability, and mood swings, especially initially
- Risk of ovarian hyperstimulation syndrome (OHSS) in women - requires careful monitoring
- Contraindicated in hormone-sensitive cancers (prostate, breast)
- Antibody formation possible with long-term use, potentially reducing efficacy
- May cause fluid retention and edema
- Precocious puberty risk in pediatric patients if used inappropriately
- Thromboembolism risk may be elevated - caution in patients with history of clots
References
Spermatogenesis Induction with HCG/FSH (2018)
Combined HCG and FSH therapy induces spermatogenesis in 70-90% of men with hypogonadotropic hypogonadism. HCG stimulates testosterone production while FSH supports spermatogenesis.
View Study (opens in new tab) →Ovulation Induction Success Rates (2017)
HCG trigger for ovulation induction achieves pregnancy rates of 15-25% per cycle in clomiphene/letrozole protocols and higher in gonadotropin stimulation cycles.
View Study (opens in new tab) →Cryptorchidism Treatment Meta-Analysis (2014)
Meta-analysis of HCG for cryptorchidism showing ~25% success rate for hormonal treatment. Surgery remains more effective but HCG/GnRH may have role in bilateral cases or combined therapy.
View Study (opens in new tab) →Quick Start Guide
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