Human Chorionic Gonadotropin (hCG)

Human chorionic gonadotropin is a glycoprotein hormone naturally produced by the placenta during pregnancy. Its biological role in pregnancy is to maintain the corpus luteum's progesterone production during the first trimester, supporting the uterine environment until placental progesterone production takes over. It is the hormone detected by pregnancy tests — present in pregnancy urine and blood at concentrations far exceeding non-pregnant baseline.^[1]

HCG is structurally similar to luteinizing hormone (LH) — the two share an alpha subunit and have substantially overlapping beta subunits. This structural similarity translates to functional identity at the receptor level: HCG binds and activates the LH receptor with high affinity, producing the same downstream biology that LH does. The key difference is duration of action — HCG has a much longer half-life (~36 hours vs LH's 20-30 minutes), making it useful as a pharmacological LH agonist where sustained receptor activation is needed.

Pharmaceutical HCG is produced through two routes: extraction from the urine of pregnant women (the traditional source, sold as Pregnyl, Novarel, and similar) and recombinant production (Ovidrel/Ovitrelle). Both are clinically equivalent for most indications, though the recombinant form has reduced lot-to-lot variability and no theoretical contamination concerns from the urinary source.

HCG's mechanism is straightforward — it is an LH receptor agonist with extended duration of action. Activation of LH receptors produces effects that depend on where those receptors are located:

• In testicular Leydig cells — LH receptor activation stimulates testosterone production. This is the basis of HCG's TRT-adjunct, fertility, and post-cycle therapy applications in men.
• In ovarian theca cells — LH receptor activation stimulates ovarian steroidogenesis and is part of the cascade triggering ovulation. This is the basis of HCG's use as an ovulation trigger in IVF and ovulation induction.
• In ovarian granulosa cells — LH receptor activation is also involved in oocyte maturation, which is why HCG specifically triggers the final maturation step needed for retrieval in assisted reproduction.

The receptor pharmacology is well-characterized and reasonably predictable. The therapeutic effects flow from the same biology that endogenous LH produces — HCG is essentially pharmacological LH with longer duration.

The peer-reviewed literature on HCG is summarized below across two tiers: human research (the highest standard), and preclinical / emerging research (animal models and early-stage human work).

This table summarizes commonly discussed claims and how the published evidence weighs in. The aim is clarity — supported claims, claims that look promising but need more data, and claims that outrun the science.

HCG is administered by subcutaneous or intramuscular injection. It comes as a lyophilized powder requiring reconstitution before use, with bacteriostatic water as the standard diluent. Once reconstituted, it requires refrigeration and is typically stable for 30-60 days depending on preservative content.

For TRT-adjunct testicular preservation: the most common community and clinical protocol is 250-500 IU subcutaneously, two to three times per week, run continuously alongside testosterone therapy. Lower doses (250 IU twice weekly) often produce adequate testicular volume preservation; higher doses may produce more estrogenic side effects without proportionally greater benefit.

For post-cycle therapy: protocols vary but typically run HCG for 2-4 weeks at higher doses (1000-2500 IU every other day) immediately following the end of the suppressive cycle, then transition to SERMs (clomiphene or tamoxifen) for HPG axis restart. The specific protocol depends on the prior cycle, individual response, and clinician judgment.

For fertility induction (men with hypogonadotropic hypogonadism): typical doses are 1000-3000 IU two to three times per week, often combined with FSH or hMG (menotropins) to support spermatogenesis. Treatment duration is typically months.

For ovulation induction / IVF trigger: a single dose of 5,000-10,000 IU (or 250 mcg recombinant) is administered to trigger ovulation roughly 36-40 hours later.

HCG should not be used by anyone for whom estrogen elevation, increased blood viscosity, or anabolic steroid restoration would be clinically problematic without medical supervision.

HCG is one of the most clinically established peptide hormones, with decades of use in fertility, reproductive endocrine, and (off-label) TRT-adjunct and PCT contexts. The mechanism is well-characterized (long-acting LH receptor agonism), the indications are well-validated for the approved uses, and the TRT-adjunct application has substantial mechanistic and clinical-experience support. The HCG diet for weight loss is unsupported by controlled evidence and persists despite that.

For users on TRT considering HCG for testicular preservation and fertility maintenance, the clinical case is solid and the protocols are well-established. For users in PCT contexts, HCG has a standard role within the broader recovery protocol. For users encountering HCG in weight-loss marketing, the controlled-trial evidence does not support specific HCG effects beyond the caloric restriction the protocol enforces. As with most peptide hormones with grey-market availability, source quality matters substantially — pharmaceutical-grade HCG from established channels is meaningfully different from variable-quality compounded or research-grade product.