Mechanism · Research Data · Protocols · Compound Information
Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone naturally produced by the placenta during pregnancy, where it supports maintenance of the corpus luteum and early gestational progesterone output. Unlike most peptides discussed on this site, hCG is not an investigational research compound — it is a long-established, licensed medicine with a decades-long clinical history and several genuinely approved indications.
It is important to separate three distinct categories of hCG use, because they carry very different levels of evidence: (1) approved medicinal indications — fertility treatment, ovulation induction, hypogonadotropic hypogonadism, and cryptorchidism, all supported by extensive clinical data and regulatory approval; (2) off-label adjunctive use in testosterone replacement therapy (TRT) protocols, where low-dose hCG is used to preserve testicular size and endogenous function — a rational, published but comparatively smaller evidence base; and (3) the historic "hCG diet" for weight loss, which is not supported by quality clinical evidence and has drawn direct regulatory pushback. This guide addresses all three transparently.
| Evidence Type | Status |
|---|---|
| Regulatory Approval (fertility / hypogonadism / cryptorchidism) | ✔ Approved medicine (e.g. Pregnyl, Ovidrel, Novarel) |
| Human RCTs — fertility / IVF trigger | ✔ Extensive, decades of data |
| Human studies — TRT-adjuvant testicular preservation | ✔ Published but smaller evidence base (off-label use) |
| Human evidence — weight loss ("hCG diet") | ✗ Not supported; regulatory action taken against marketing claims |
| Animal / In Vitro Studies | ✔ Extensive historic physiology research |
hCG shares a near-identical alpha subunit with luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). Its unique beta subunit confers specificity for the LH/hCG receptor (LHCGR), a G-protein coupled receptor. In the testis, hCG binds LHCGR on Leydig cells, stimulating testosterone production in the same manner as endogenous LH. In the ovary, a surge of hCG (or LH) triggers final oocyte maturation and ovulation via action on theca and granulosa cells. A key pharmacological distinction from endogenous LH is hCG's considerably longer circulating half-life, which is clinically exploited — a single hCG injection can sustain LH-receptor stimulation far longer than a natural LH pulse.
hCG has been used for decades as a "trigger shot" in assisted reproduction to induce final follicular maturation and ovulation ahead of oocyte retrieval or timed intercourse. This is one of the most extensively studied applications of any hormone in reproductive medicine. A major area of ongoing comparative research examines hCG trigger versus GnRH agonist trigger, particularly regarding the risk of ovarian hyperstimulation syndrome (OHSS) — GnRH agonist triggers are generally associated with lower OHSS risk in high-responder patients, a finding replicated across multiple reviews (e.g. work summarised by Humaidan P et al.).
In men with hypogonadotropic hypogonadism (low LH/FSH signalling from the pituitary or hypothalamus), hCG is used clinically to stimulate Leydig cell testosterone production and support spermatogenesis, often alongside FSH-containing preparations. This is a well-established, licensed indication.
Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal (HPG) axis, reducing endogenous LH and FSH output, which in turn reduces testicular volume and intratesticular testosterone, impacting fertility potential. Some TRT protocols incorporate low-dose hCG off-label specifically to maintain LHCGR stimulation independent of the suppressed pituitary signal. Published research, including work by Hsieh TC et al. and Coward RM et al., has examined hCG co-administration as a strategy to preserve intratesticular testosterone and spermatogenic potential during testosterone therapy. This application has a rational endocrine basis and a growing but still comparatively limited published literature relative to the core fertility indications, and is not itself a licensed indication for hCG.
hCG has historically been used in attempts to stimulate testicular descent in boys with cryptorchidism (undescended testicle). Surgical orchidopexy is now generally regarded as first-line management, with hCG playing a more limited, historically significant role.
Since the 1950s, hCG has been marketed for weight loss combined with very-low-calorie diets (the "hCG diet"). This use is not supported by quality clinical evidence — controlled trials have not demonstrated that hCG itself produces weight loss beyond what the accompanying caloric restriction alone would achieve. Regulatory bodies, including the FDA, have taken enforcement action against hCG weight-loss product marketing, and over-the-counter "homeopathic hCG" weight-loss products have been required to carry disclaimers stating that hCG has not been demonstrated to be effective for weight loss. This use case is included here for completeness and to be explicit that it is not evidence-supported.
| Study / Source | Focus | Key Finding |
|---|---|---|
| Hsieh TC et al. 2013, Journal of Urology | Low-dose hCG in men on TRT | Concomitant low-dose hCG helped maintain intratesticular testosterone during testosterone replacement therapy |
| Coward RM et al. / Wenker EP et al., Journal of Sexual Medicine / Journal of Urology | Fertility preservation during testosterone therapy | hCG-based combination therapy associated with recovery/support of spermatogenesis around testosterone use |
| Humaidan P et al., Human Reproduction / Human Reproduction Update | hCG vs GnRH agonist trigger in IVF | GnRH agonist trigger associated with lower OHSS risk than hCG trigger in high-responder patients |
| Choi J & Smitz J 2014, Molecular and Cellular Endocrinology | Review of hCG physiology and receptor biology | Characterised hCG-LHCGR signalling and clinical applications across reproductive contexts |
| FDA/FTC regulatory record | hCG weight-loss product marketing | Enforcement action and mandated disclaimers stating no demonstrated weight-loss efficacy |
⚠️ Stack combinations listed for research reference only. Not safety or efficacy guidance.
experimental research protocols only — not dosing recommendations.
| Context | Protocol Feature Studied |
|---|---|
| IVF trigger | Single trigger dose timed prior to oocyte retrieval, compared against GnRH agonist trigger timing in published protocols |
| Male hypogonadotropic hypogonadism | Intramuscular or subcutaneous dosing regimens combined with gonadotropin co-therapy in clinical literature |
| TRT-adjuvant (off-label) | Low-dose, intermittent dosing studied alongside testosterone therapy in published cohort research |
OHSS is a well-documented, sometimes serious complication specifically associated with hCG-triggered ovulation induction and is a major driver of the ongoing research comparing hCG trigger against GnRH agonist trigger protocols.
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