HCG (Human Chorionic Gonadotropin)

Human chorionic gonadotropin (HCG) is a heterodimeric glycoprotein sharing a common alpha subunit with LH, FSH, and TSH, paired with a unique beta subunit bearing a 24-amino-acid C-terminal extension not present in LH. This extension prolongs serum half-life to 24-36 hours, compared with approximately 60 minutes for LH, producing a sustained biological signal from a single injection.

HCG binds the luteinizing hormone/choriogonadotropin receptor (LHCGR), a G protein-coupled receptor expressed on testicular Leydig cells and ovarian theca and granulosa cells. Binding activates adenylyl cyclase via Gαs, raising intracellular cyclic AMP (cAMP), which activates protein kinase A (PKA) and downstream phosphorylation of ERK1/2 and the transcription factor CREB. Both the PKA and MEK/ERK pathways are obligatory for steroidogenesis; pharmacological inhibition of either suppresses testosterone production.

The key downstream effector is steroidogenic acute regulatory protein (STARD1), which transports cholesterol across the inner mitochondrial membrane — the rate-limiting step in steroid synthesis — initiating the enzymatic cascade from cholesterol to pregnenolone and ultimately to testosterone.

HCG is approximately 10-fold more potent than LH in cAMP stimulation (EC50 approximately 18.6 pM versus 192 pM for LH), yet net testosterone output converges at saturating doses in Leydig cells, indicating downstream signal equivalence.

In the ovary, HCG mimics the midcycle LH surge, triggering final oocyte maturation and ovulation approximately 36-40 hours after administration, which is the basis of its use as a trigger agent in assisted reproduction.

HCG is FDA-approved for three indications: prepubertal cryptorchidism not due to anatomical obstruction, hypogonadotropic hypogonadism (HH) in males, and induction of ovulation in anovulatory women.

In male HH, Sahib et al. (Cureus, 2023; n=51) compared hCG monotherapy, hCG plus human menopausal gonadotropin (hMG), and a sequential regimen. Maximum testosterone was 413.6 ± 58.7 ng/dL with hCG alone versus 710.4 ± 102.7 ng/dL with combination therapy (p=0.031). Spermatogenesis rates of 25-33% across groups showed no significant intergroup difference (p=0.882). Broader literature indicates that combined hCG plus recombinant FSH achieves spermatogenesis in approximately 84% of IHH patients and sperm concentrations above 1.5 x 10^6/mL in 69.1%, versus roughly 40% with hCG monotherapy.

Roth et al. (Journal of Clinical Endocrinology and Metabolism, 2010; PMID 20484472; n=37 men with induced gonadotropin deficiency) demonstrated a dose-dependent rise in intratesticular testosterone from 77 nmol/L (no hCG) to 923 nmol/L with 125 IU subcutaneously every other day (P<0.001). In a related study, 500 IU hCG every other day co-administered with testosterone enanthate (200 mg/week) maintained intratesticular testosterone 26% above baseline, while testosterone alone caused 94% suppression.

Agarwal et al. (Global Pediatric Health, 2020; PMID 35187206; n=52 adolescent HH males) found hCG produced significantly greater mean testicular volume than testosterone therapy (8.25 vs 3.4 mL, P<0.001), with no significant differences in penile length, growth velocity, or serum testosterone, suggesting hCG may be preferable when preserving testicular development and future fertility is a priority.

Rainer et al. (Cureus, 2022; n=28 men with prior TRT) found hCG monotherapy (1,000-2,000 IU/week) reduced hematocrit from 45.27% to 44.16% (p<0.05), with no thromboembolic events over approximately 11 months. Seventy-one percent of symptomatic patients reported improvement in erectile function and energy.

For weight loss, a meta-analysis by Lijesen et al. (DARE, 1995; 14 RCTs; n=556) found that 12 of 14 trials showed no greater weight reduction with hCG than with placebo or caloric restriction alone. The FDA has not approved hCG for weight loss, and its use for this purpose is not supported by evidence.

Typical dosage: 250-500 IU (multiple weekly).

FDA-approved parenteral regimens (Pregnyl and equivalent formulations, administered by injection):

• Prepubertal cryptorchidism (children aged 4-9): 4,000 USP units intramuscularly three times weekly for 3 weeks; or 5,000 USP units every second day for 4 injections; or 500-1,000 USP units given as 15 injections over 6 weeks; or 500 USP units three times weekly for 4-6 weeks, repeated at 1,000 USP units if the first course is unsuccessful.

• Hypogonadotropic hypogonadism in males: 500-1,000 USP units intramuscularly three times weekly for 3 weeks, then twice weekly for 3 weeks; alternatively, 4,000 USP units three times weekly for 6-9 months, followed by 2,000 USP units three times weekly for a further 3 months.

• Ovulation induction: 5,000-10,000 USP units intramuscularly given one day after the last FSH dose. In IVF protocols, doses may be reduced to 3,300-5,000 IU in predicted high responders to reduce ovarian hyperstimulation syndrome risk without compromising oocyte yield.

• Off-label for fertility preservation during testosterone replacement therapy: 250-500 IU subcutaneously every other day, derived from clinical research by Roth et al. and Coviello et al. For fertility restoration following TRT cessation, 3,000 IU every other day for three or more months, sometimes combined with recombinant FSH or a SERM, has been reported in clinical practice but lacks dedicated RCT data.

This information is provided for educational purposes only and does not constitute medical advice. All dosage, formulation, and monitoring decisions must be made by a qualified and licensed physician.

No compound-specific stability data has been identified for this peptide. The general lyophilized-peptide handling framework applies — see Storage & handling for temperature, reconstitution diluent, and beyond-use dating principles.

The best-supported combination is hCG with recombinant FSH or hMG for male IHH when hCG monotherapy fails to induce adequate spermatogenesis after 6-12 months, particularly in men with baseline testicular volume below 4 mL. Adding FSH raises spermatogenesis rates from approximately 40% with hCG alone to approximately 84% with combined therapy, and this approach is endorsed in clinical endocrinology practice.

Co-administration of low-dose hCG with exogenous testosterone during TRT is supported by published clinical research for maintaining intratesticular testosterone and preventing testicular atrophy and azoospermia; 250-500 IU subcutaneously every other day is the dose derived from this research.

Combination with aromatase inhibitors such as anastrozole to control hCG-driven estradiol elevation is widely used in clinical practice. Evidence for this specific combination is observational and anecdotal rather than from controlled trials.

Combination with selective estrogen receptor modulators (clomiphene citrate, tamoxifen) has been reported for post-anabolic-steroid recovery and functional HH. A systematic review found that SERM plus hCG produced higher testosterone levels than hCG alone, though controlled data specific to this combined off-label use are limited. Community use of hCG with SERMs during or after anabolic steroid cycles is largely anecdotal.

HCG (Human Chorionic Gonadotropin) is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

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Reported side effects: Possible estrogen increase, injection site reactions

In males, the primary adverse effect is dose-dependent estradiol elevation from aromatization of hCG-stimulated testosterone, which can cause gynecomastia, fluid retention, and mood changes. Gynecomastia risk appears higher when hCG is combined with exogenous testosterone. Precocious puberty may occur in prepubertal boys, manifesting as deepened voice, pubic hair growth, and increased acne, representing a predictable pharmacological effect rather than an idiosyncratic reaction.

A retrospective study (Rainer et al., 2022; n=28) found hCG monotherapy associated with a reduction in hematocrit from 45.27% to 44.16% (p<0.05) and no thromboembolic or cardiovascular events over approximately 11 months, suggesting a potentially more favorable erythrocytosis profile compared with direct testosterone administration.

In women undergoing ovulation induction or IVF, ovarian hyperstimulation syndrome (OHSS) is the most serious risk, ranging from mild abdominal discomfort and ovarian cyst formation to life-threatening ascites, pleural effusion, and arterial or venous thromboembolism. OHSS may begin within 24 hours of hCG and typically peaks at 7-10 days. High-responder patients are at greatest risk; sliding-scale dosing and GnRH agonist trigger protocols are used to mitigate this. Additional fertility-treatment risks include multiple gestation, adnexal torsion, ectopic pregnancy, and ovarian cyst rupture.

Rare systemic effects include hypersensitivity reactions and anaphylaxis.

Absolute contraindications include androgen-dependent neoplasms such as prostate carcinoma, precocious puberty, and prior hypersensitivity to any hCG preparation. Caution is warranted in patients with cardiac or renal disease, epilepsy, migraine, or asthma, where androgen-mediated sodium retention may exacerbate edema. Use for weight loss is unsupported by evidence and potentially harmful in individuals with androgen-sensitive conditions.