HCG
HormonalPreclinicalAlso known as: Human Chorionic Gonadotropin
Human chorionic gonadotropin (hCG) is a 237-amino-acid glycoprotein hormone produced naturally during pregnancy by trophoblast cells of the developing embryo, beginning as early as 6-8 days after conception and peaking between weeks 8-11 of gestation at concentrations of 50,000-300,000 mIU/mL maternal serum. The hormone is a heterodimer consisting of two distinct subunits: an alpha subunit (92 amino acids, 14.5 kDa, shared with LH, FSH, and TSH) and a unique beta subunit (145 amino acids, 22 kDa, which gives hCG its biological specificity and is the basis for pregnancy tests).
Overview
At A Glance
hCG signals primarily through the LH/CG receptor (LHCGR), a G-protein-coupled receptor expressed densely on: - Leydig cells in the testis (testosterone and estradiol production) - Theca cells of the ovary (androgen production) - Granulosa cells of mature follicles (estrogen produ…
Mechanism of Action
hCG signals primarily through the LH/CG receptor (LHCGR), a G-protein-coupled receptor expressed densely on:
- Leydig cells in the testis (testosterone and estradiol production)
- Theca cells of the ovary (androgen production)
- Granulosa cells of mature follicles (estrogen production and ovulation triggering)
- Corpus luteum (progesterone production to support early pregnancy)
- Smaller populations on uterine tissue, placental tissue, and certain immune cells
LHCGR Signaling Cascade: LHCGR is predominantly coupled to Gαs, so hCG binding activates adenylyl cyclase, increases intracellular cAMP, activates protein kinase A, and triggers:
- Upregulation of steroidogenic enzymes (StAR, CYP17A1, CYP11A1, 3β-HSD) in gonadal cells
- Cholesterol transport into mitochondria for steroid synthesis
- Rapid increases in testosterone (men) or estrogen/progesterone (women) production
- At higher doses, secondary activation of phospholipase C and intracellular calcium mobilization
Testicular Effects in Men:
- Leydig cell stimulation: the primary action. hCG at physiological doses (500-3,000 IU) produces strong testosterone responses in men with intact Leydig cells. Testosterone elevation is detectable within hours and peaks 48-72 hours post-injection.
- Preservation of testicular size: direct Leydig cell stimulation prevents the atrophy that occurs when LH is suppressed. This is the primary rationale for TRT co-administration.
- Spermatogenesis support: Sertoli cells produce the high intratesticular testosterone needed for spermatogenesis. hCG-driven Leydig cell testosterone production supports this local process, though FSH is also required for full spermatogenesis restoration. For men on TRT attempting to restore fertility, hCG + FSH (or hMG for combined LH/FSH activity) is often used.
- Intratesticular estradiol production: hCG-stimulated aromatization in Leydig cells produces local estradiol that is important for normal testicular function.
Ovarian Effects in Women:
- Ovulation triggering: at peak follicular maturation, a large hCG dose (5,000-10,000 IU IM/SC) substitutes for the endogenous LH surge, triggering oocyte maturation and ovulation within 34-42 hours. This is the standard "trigger shot" used in IVF and timed intercourse cycles.
- Luteal phase support: lower-dose hCG after ovulation supports the corpus luteum and progesterone production, supporting early pregnancy establishment.
- Controlled ovarian hyperstimulation: hCG can substitute for LH in dual-trigger protocols alongside GnRH agonists.
Pharmacokinetics:
- Half-life: 24-36 hours (much longer than LH's 20-30 min half-life)
- Peak plasma concentration: 6-12 hours after intramuscular or subcutaneous injection
- Biological effect duration: 5-7 days from a single dose
- Clearance: primarily renal, with some hepatic metabolism
- Bioavailability SC ≈ IM (both well-absorbed from injection sites)
- No oral bioavailability (like all large glycoprotein hormones)
Source Types:
- Urinary-derived hCG (u-hCG): extracted from pregnant women's urine. Historically dominant supply. Brand names include Pregnyl, Novarel, Profasi (where still available). Some lot-to-lot variability in purity.
- Recombinant hCG (r-hCG): produced in CHO cells; brand names Ovidrel (US) and Ovitrelle (elsewhere). Higher cost but more consistent quality and purity.
- Compounded hCG: produced by compounding pharmacies from bulk hCG powder. Used commonly for TRT support and weight-loss contexts. Quality varies widely by pharmacy.
Pregnancy-Specific Mechanisms (not relevant for male use but relevant biology):
- Supports corpus luteum in early pregnancy
- Maintains progesterone production until placenta takes over (weeks 8-10)
- Immunomodulatory effects supporting pregnancy tolerance
- Various non-classical effects on uterine environment
Immunogenicity: Some users develop anti-hCG antibodies with prolonged use, potentially reducing efficacy over time. Urinary-derived hCG appears slightly more immunogenic than recombinant. Cycling hCG use (breaks between courses) may reduce this risk.
Desensitization: Continuous high-dose hCG can downregulate LHCGR expression on Leydig cells over weeks to months. This is one reason cycling or moderate-dose continuous hCG is preferred over prolonged high-dose use. Classic dosing patterns (500-1,500 IU 2-3x weekly) are selected to avoid substantial receptor desensitization while maintaining efficacy.
What hCG Does NOT Do:
- Does not activate hypothalamic or pituitary axis (unlike Kisspeptin-10 or GnRH/gonadorelin)
- Does not restart suppressed endogenous LH production (it substitutes for rather than restores LH signaling)
- Does not directly restore FSH signaling (spermatogenesis may require adjunctive FSH)
- Does not produce clinically meaningful weight loss or appetite changes at any dose tested
Overview
Human chorionic gonadotropin (hCG) is a 237-amino-acid glycoprotein hormone produced naturally during pregnancy by trophoblast cells of the developing embryo, beginning as early as 6-8 days after conception and peaking between weeks 8-11 of gestation at concentrations of 50,000-300,000 mIU/mL maternal serum. The hormone is a heterodimer consisting of two distinct subunits: an alpha subunit (92 amino acids, 14.5 kDa, shared with LH, FSH, and TSH) and a unique beta subunit (145 amino acids, 22 kDa, which gives hCG its biological specificity and is the basis for pregnancy tests). Discovered and first isolated in the 1920s by researchers including Bernhard Zondek and Selmar Aschheim, hCG has become one of the most clinically important hormones in reproductive medicine — both as a diagnostic marker (pregnancy testing, tumor marker for gestational trophoblastic disease and some germ cell tumors) and as a therapeutic agent (ovulation induction, luteal phase support in IVF, induction of Leydig cell testosterone production in hypogonadotropic hypogonadism, and preservation of testicular size and fertility during exogenous androgen use).
The critical pharmacological insight about hCG is that it binds to and activates the luteinizing hormone (LH) receptor with high affinity — essentially, hCG is a long-acting LH mimetic. LH and hCG share the identical alpha subunit, and their beta subunits are highly homologous; this structural similarity means that hCG can substitute functionally for LH at the receptor level. The key pharmacokinetic difference is half-life: endogenous LH has a plasma half-life of 20-30 minutes due to rapid clearance and pulsatile secretion, while hCG has a half-life of 24-36 hours because its unique C-terminal peptide extension (CTP) and higher glycosylation protect it from rapid clearance. This long half-life makes hCG an excellent tool for sustained LH-receptor stimulation — a single injection can maintain biologically significant LH-receptor activation for 3-7 days, compared to LH's minutes-long effect (Cole, 2010).
In current clinical practice, hCG has three primary approved uses: (1) ovulation induction in women undergoing fertility treatment (often substituting for the endogenous LH surge); (2) treatment of hypogonadotropic hypogonadism in men, where it directly stimulates testicular Leydig cells to produce testosterone (bypassing the absent or insufficient endogenous LH); (3) pediatric use in cryptorchidism to promote testicular descent. In the bodybuilding and testosterone-replacement-therapy communities, hCG is widely used off-label for a different but related purpose: preserving testicular size and function during exogenous androgen use. When men inject testosterone or anabolic steroids, the body senses the elevated androgen and suppresses endogenous LH through hypothalamic-pituitary negative feedback; this causes the testes to stop producing their own testosterone and can lead to testicular atrophy and fertility impairment. Low-dose hCG (typically 500-1,500 IU 2-3x weekly) directly stimulates the testes to continue producing testosterone regardless of the suppressed LH signal, preserving testicular size and function during TRT or cycles (Hsieh et al., 2013).
The landscape of hCG use shifted significantly in the 2010s and 2020s. First, the FDA approved several forms of recombinant LH (Luveris, rLH) that achieve similar Leydig-cell stimulation without hCG's longer half-life and higher dosing requirements, though these remain significantly more expensive. Second, concerns about product sourcing and quality emerged — urinary-derived hCG (which has dominated supply historically) has had occasional contamination issues, while recombinant hCG (brand names Ovidrel/Ovitrelle) offers more consistent quality at higher cost. Third, the hCG diet — a weight-loss fad dating to Albert Simeons's 1954 publication — has been thoroughly debunked by multiple rigorous trials, and the FDA has issued warnings against hCG for weight loss. Any weight loss on the hCG diet is due to the severe 500-kcal dietary restriction, not hCG itself, which has no demonstrable effect on appetite or metabolism. Despite clear evidence of inefficacy, compounded hCG for weight loss remains a persistent grey-market product (Lijesen et al., 1995 Cochrane).
This entry focuses primarily on the men's health and fertility applications of hCG, which are the most common off-label uses in peptide communities. Cross-references include Gonadorelin (GnRH, upstream of LH/hCG in the reproductive axis), Kisspeptin-10 (further upstream, driving GnRH release), Enclomiphene (SERM that restores axis through different mechanism), and Sermorelin (distinct GH axis, frequently layered in recovery protocols). For women's fertility applications, hCG is integral to IVF and ovulation induction protocols administered under reproductive endocrinology supervision.
Chemical Information
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Interactions
Contraindications
Absolute contraindications:
- Hormone-dependent cancers (prostate cancer in men, estrogen-dependent breast cancer) — hCG drives androgen and estrogen production that can fuel these malignancies
- Known hypersensitivity to hCG preparations
- Pregnancy (for women using for non-obstetric purposes; appropriate obstetric use is different)
- Uncontrolled thromboembolic disease (recent DVT, PE)
- Precocious puberty (pediatric context)
- Active hyperthyroidism (hCG has very weak TSH-like activity that may compound)
- Gonadotropin-secreting pituitary tumors
Strong relative contraindications:
- History of hormone-sensitive cancers, even in remission, without oncology clearance
- Significant gynecomastia that would worsen with additional estradiol exposure
- Severe uncontrolled hypertension
- Recent cardiovascular event (MI, stroke within 6 months)
- Severe obesity with sleep apnea (erythrocytosis risk increased with concurrent TRT; hCG contributes)
- Active significant polycythemia (hematocrit >54)
- Severe hepatic or renal impairment (altered clearance)
- Ovarian hyperstimulation risk factors in women (PCOS, high AMH, prior OHSS)
- Active mood or psychiatric disorders affected by hormonal fluctuation
Drug interactions:
- Exogenous LH or rLH (Luveris): redundant at the receptor; choose one
- GnRH agonists at suppressive doses (leuprolide/Lupron for prostate cancer): pharmacologically opposed
- Aromatase inhibitors (anastrozole, letrozole): complementary management of estradiol; not contraindicated but must be carefully titrated
- SERMs (clomiphene, tamoxifen, enclomiphene): complementary in post-cycle protocols
- Corticosteroids: may blunt response; monitor
- Warfarin or other anticoagulants: estrogen elevation can affect coagulation parameters; monitor INR more frequently if significant estradiol changes
Stop using if:
- Any cardiovascular event (chest pain, new arrhythmia, stroke symptoms)
- Signs of thromboembolism (unexplained leg swelling, shortness of breath, chest pain)
- Rapidly progressive gynecomastia despite aromatase inhibitor
- Severe allergic reaction
- New prostate symptoms (significant PSA rise, concerning DRE)
- Precocious puberty signs in any pediatric user
- Ovarian hyperstimulation symptoms in women (severe abdominal pain, rapid weight gain, shortness of breath)
- Pregnancy (in non-obstetric users)
- Active cancer diagnosis
Monitoring:
For men's use:
- Baseline: total and free testosterone, estradiol (sensitive LC-MS/MS assay), SHBG, LH, FSH, CBC, PSA, complete metabolic panel
- 4-6 weeks after starting: testosterone, estradiol, hematocrit
- 3-6 months: full panel repeat
- Annually thereafter: continued monitoring for lipids, PSA, hematocrit, complete hormones
For women's use:
- Requires reproductive endocrinology supervision with specific protocols for each cycle
- Ultrasound monitoring in ovulation induction contexts
- hCG quantification for pregnancy confirmation and monitoring
Special Considerations:
- Prostate cancer surveillance: hCG doesn't change surveillance intervals but should be discussed with oncology/urology if significant PSA changes occur
- Fertility documentation: if fertility is the goal, semen analysis every 3 months during restoration protocols
- Cardiovascular risk: manage as for TRT — blood pressure, lipid profile, hematocrit, cardiovascular symptoms
- Bone density: in long-term use in hypogonadal men, DEXA scan at baseline and every 2-3 years supports bone health monitoring
Pregnancy-Specific Considerations:
- Exogenous hCG causes positive pregnancy tests for days to weeks after injection
- Couples trying to conceive need to plan pregnancy testing accordingly
- hCG during pregnancy (for obstetric indications only, under specialist supervision) is different from off-label use
Medical Supervision:
hCG benefits from clinician supervision particularly for:
- Long-term TRT + hCG combinations
- Fertility restoration protocols
- Complex post-cycle recovery
- Users with cardiovascular, prostate, or metabolic comorbidities
- Anyone using hCG monotherapy for chronic hypogonadism management
Men's health clinics, urology practices with TRT expertise, and endocrinology practices are appropriate supervision sources. Reproductive endocrinology for fertility-specific use.
Research Disclaimer
This interaction data is compiled from published research and community reports. It may not be exhaustive. Always consult a healthcare professional before combining compounds.
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Frequently Asked Questions
Why do men on TRT add hCG?
When men inject testosterone, their brain senses the elevated androgen and shuts down the endogenous LH signal that normally tells their testes to produce testosterone. Without LH stimulation, the testes shrink (testicular atrophy) and stop producing their own testosterone and sperm. hCG mimics LH at the testicular receptor, so it directly stimulates the testes to keep producing testosterone and supporting spermatogenesis regardless of the suppressed endogenous LH. Co-administering low-dose hCG (typically 500 IU 2x weekly) with TRT preserves testicular size, maintains some endogenous testosterone production, and preserves fertility potential. It's become the standard of care for men on TRT who want to maintain these functions.
Does hCG cause gynecomastia?
Yes — hCG commonly elevates estradiol more than equivalent doses of exogenous testosterone do, because hCG specifically activates testicular aromatase to produce local estradiol. This is a predictable pharmacological effect rather than a random adverse reaction. Managing it: (1) keep hCG doses moderate (500 IU 2-3x weekly usually optimal); (2) monitor estradiol with sensitive assay 24-48 hours after hCG dose; (3) add low-dose anastrozole (0.5 mg 1-2x weekly) if estradiol rises excessively with symptoms; (4) don't crush estradiol — target 30-50 pg/mL, not zero. Early signs to watch for: nipple sensitivity, mild breast tissue feeling, puffy appearance under nipple. If gynecomastia becomes established and painful, tamoxifen or raloxifene can help; rarely surgery is needed.
How is hCG different from Gonadorelin or Kisspeptin-10?
They act at different points in the HPG axis. Kisspeptin-10 acts at the hypothalamus to drive GnRH release. Gonadorelin is synthetic GnRH, acting at the pituitary to drive LH/FSH release. hCG acts at the gonads directly, substituting for LH at the Leydig cell receptor. If the hypothalamus is the problem, kisspeptin is upstream; if the pituitary is the problem, gonadorelin; if you just want direct testicular stimulation (as in TRT co-administration), hCG. In post-cycle recovery, these can be combined layered approach. In TRT co-administration, hCG is the standard because the hypothalamic-pituitary axis is intentionally suppressed by exogenous testosterone and upstream stimulation is futile — direct gonadal stimulation is the only viable approach.
Can hCG help with weight loss?
No. The hCG diet has been thoroughly debunked. Multiple high-quality randomized trials have shown that hCG injections plus the 500-kcal diet produce exactly the same weight loss as placebo injections plus the 500-kcal diet — all weight loss is attributable to the severe caloric restriction, not hCG. hCG has no effect on appetite, metabolism, or fat distribution. The FDA has issued warnings against hCG for weight loss since 2011, and the American Medical Association and other organizations have repeatedly stated there is no scientific support. If you want effective weight loss with peptides, look at GLP-1-class drugs like Tirzepatide, Retatrutide, or Semaglutide — those work through completely different mechanisms and produce 15-25% weight loss in rigorous trials. hCG does not.
Can I restore my fertility after years on TRT using hCG?
Usually yes, but it takes time and typically requires adding FSH. TRT suppresses both LH (testosterone production) and FSH (direct spermatogenesis). hCG alone restores Leydig testosterone production and often restores spermatogenesis partially, but for full fertility restoration most men need hCG + FSH (hMG or recombinant FSH). Typical protocol: stop TRT, hCG 2,000-3,000 IU 3x weekly + FSH 75-150 IU 3x weekly, continue 3-12 months. Semen analysis every 3 months. Success rates: 60-80% achieve some sperm in ejaculate within 6-12 months; 40-70% achieve fertility. Work with a reproductive urologist or endocrinologist for best outcomes. Don't try this solo — fertility work benefits enormously from specialist guidance.
What doses of hCG are safe long-term?
For TRT fertility preservation: 500-1,000 IU 2-3x weekly for years has a good safety record in clinical practice. For hypogonadotropic hypogonadism monotherapy: 1,000-2,000 IU 2-3x weekly long-term is also well tolerated. Higher doses (2,500-3,000 IU multiple times weekly) are typically reserved for fertility restoration and used shorter-term (months rather than years). Very high doses (4,000+ IU per injection) should be avoided chronically — minimal added benefit, more estradiol elevation, greater desensitization risk. Cycling (8-12 weeks on, 2-4 weeks off) may reduce immunogenicity over multi-year use but isn't strictly necessary. Regular labs and clinical monitoring support long-term safe use.
Will hCG affect my PSA or prostate?
hCG doesn't directly affect prostate tissue, but the testosterone it produces does — same considerations as TRT. Expected: mild PSA rise (usually 0.2-0.5 ng/mL) when testosterone normalizes from hypogonadal levels. Concerning: rapid PSA rise (>0.75 ng/mL in a year), new-onset urinary symptoms, or PSA crossing typical age-related thresholds. Men on hCG or TRT should have baseline PSA, repeat at 3-6 months, then annually. Men with known prostate cancer risk factors (family history, African descent, age >50) should have more intensive monitoring. hCG use doesn't prevent prostate cancer screening recommendations — continue age-appropriate surveillance. Active prostate cancer is an absolute contraindication to hCG use (as it is to TRT).
How do I know if my compounded hCG is good quality?
Several signals: (1) Source from reputable compounding pharmacies with established reputations and licensed compounding (ask your prescriber about compounder credentials); (2) Label should clearly show concentration, compounding date, beyond-use date, and lot number; (3) Lyophilized powder should be a clean white cake, not discolored or clumpy; (4) Reconstituted solution should be clear and colorless; (5) Biological verification: expected dose should produce expected testosterone response within 48-72 hours — if your 500 IU dose produces no testosterone elevation at all, product quality may be poor. For consistent protocols, stick with one pharmacy or brand to avoid variability confusing dose-response. Pharmaceutical brands (Pregnyl, Novarel, Ovidrel) eliminate compounding variability entirely.
Can I use hCG without exogenous testosterone?
Yes, and for some men this is the preferred approach. hCG monotherapy (typically 1,500-2,500 IU 2-3x weekly) can normalize testosterone in men with intact Leydig cells and secondary (pituitary-origin) hypogonadism. Advantages: preserves endogenous fertility potential, maintains testicular size, may feel more 'natural' subjectively. Disadvantages: requires more injections than TRT-only, estradiol management is more active, product cost may be higher. hCG monotherapy doesn't work for primary hypogonadism (where Leydig cells are damaged or absent — as in Klinefelter syndrome, post-orchiectomy, post-chemotherapy destruction of testicular tissue). For secondary hypogonadism (low T from pituitary/hypothalamic dysfunction), hCG monotherapy is a reasonable alternative to TRT, particularly for men prioritizing fertility preservation.
What happens if I stop hCG suddenly?
Nothing dramatic or dangerous. hCG doesn't create physical dependence or withdrawal. If you stop hCG: (1) if you're on TRT concurrently, your testicles will gradually atrophy again over 2-4 weeks as they lose the direct stimulation; testosterone levels from TRT remain stable; (2) if hCG is your only source of testosterone stimulation, your testosterone will gradually decline over 2-3 weeks as the hCG clears and no endogenous LH replaces it. If you're using hCG during post-cycle recovery, stopping prematurely may result in incomplete axis restoration — longer protocols tend to produce better recovery outcomes. If you're stopping due to side effects, the hormonal effects (testosterone, estradiol) normalize within 1-3 weeks. Always taper rather than stop abruptly for longer protocols; taper can be over 2-4 weeks.
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