Gonadorelin and hCG are compared because men on testosterone therapy are told one can stand in for the other: both are used to keep the testes working while external testosterone switches off the body's own signal. They act at different points on the same hormone axis, they have very different regulatory records, and only one of them has ever been published in the setting where the comparison is being made. This page sets the two records side by side. It is a table, not a verdict — there is no "better" here, and a decision about either belongs with a urologist or endocrinologist. The full dose records are on our gonadorelin dosage page and hCG dosage page; the hCG adverse-event record is on our hCG side-effects page. How brands appear on this site is on our disclosure page.
Where each one acts
The chain runs hypothalamus → pituitary → testis. The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses; the pituitary answers with luteinising hormone (LH), which drives testosterone production in the testis, and follicle-stimulating hormone (FSH), which supports sperm production. External testosterone suppresses the top of that chain through feedback, so LH and FSH fall and the testes, deprived of their signal, make less testosterone of their own and less sperm.
Gonadorelin is synthetic GnRH — the natural ten-amino-acid sequence. It acts at the pituitary, so its effect depends on the pituitary being able to respond. It also depends on timing: pulsatile GnRH stimulates LH and FSH release, while a continuous stimulus at the same receptor desensitises it and shuts that release down, which is the basis of the whole GnRH-agonist class used to suppress sex hormones.
hCG is a placental glycoprotein that binds the same receptor on the testis as LH. It bypasses the hypothalamus and pituitary entirely, so it works whatever the feedback is doing upstream — but it supplies only the LH-like signal, not FSH.
The comparison
| Gonadorelin | hCG | |
|---|---|---|
| What it is | GnRH, a 10-amino-acid peptide | Chorionic gonadotropin, a two-chain glycoprotein |
| Acts on | The pituitary (releases LH and FSH) | The testis (LH receptor), directly |
| Current US human label | None — Factrel and Lutrepulse both discontinued; the five current labels are for cattle | Yes — Pregnyl, Novarel, generic chorionic gonadotropin, and recombinant Ovidrel (a fertility label) |
| Labelled male use | — | "Selected cases of hypogonadotropic hypogonadism in males" |
| Dose shape in the human record | 1–20 µg per pulse, every 90–120 minutes, by pump | Hundreds to thousands of units, a few times a week, by injection |
| How long it lasts | Back to baseline within 60 min (IV) or over 120 min (SC) after 5 µg (Handelsman 1984) | Elimination half-life 29 ± 6 h (Ovidrel label, SC) |
| Published alongside testosterone therapy | No study found | One retrospective series, 26 men (Hsieh 2013) |
| Compounding | Not affected by the 2020 biologics transition | Lost the 503A/503B exemptions on 2020-03-23 as a licensed biological product |
The one head-to-head trial
Gong and colleagues (J Clin Endocrinol Metab 2015;100(7):2793-9) treated boys aged 10 to 16 with hypogonadotropic hypogonadism — a condition in which the hypothalamic or pituitary signal is missing from birth. Twelve received 8 to 10 µg of GnRH under the skin every 90 minutes by pump; 22 received intramuscular hCG, starting at 1,000 units twice a week and rising to 2,000 units every other day, for 12 to 14 months. The GnRH group ended with larger testes. Both groups gained testosterone and penile length, with no significant difference between them, and the authors reported no significant difference in side effects.
Three limits keep that result from answering the adult question. The patients were adolescents with a congenital disorder, not men whose axis was switched off by testosterone. The abstract describes no randomisation or blinding, and the trial was small. And the gonadorelin arm used a pump delivering a pulse every 90 minutes around the clock — the delivery the whole GnRH literature uses because the interval decides whether the effect is stimulation or suppression. A once- or twice-daily injection is a different exposure pattern, and no study compared it with hCG.
What exists alongside testosterone therapy
For hCG, a small record. Hsieh and colleagues (J Urol 2013;189(2):647-50) reviewed 26 men, mean age 35.9, on testosterone gel or weekly injections plus 500 units of hCG every other day. Over a mean follow-up of 6.2 months, semen parameters did not change, no man became azoospermic, and nine partners became pregnant. It was retrospective, uncontrolled and from one practice, and the authors' own conclusion is hedged — hCG "appears to maintain semen parameters". It is still the kind of evidence the gonadorelin side of the table does not have.
For gonadorelin, none. A PubMed search on 2026-09-27 combining gonadorelin or pulsatile GnRH with testosterone therapy and testicular or spermatogenesis outcomes returned ten records. They are studies of congenital hypogonadism with a GnRH pump, a gene report, a renal-failure review, feedback physiology and three rhesus-monkey studies; none gave gonadorelin to men receiving testosterone. The whole gonadorelin literature indexed under that name runs to 296 records. The mechanism also leaves a real question open rather than a presumption either way: testosterone suppresses the pituitary through feedback, and gonadorelin works by stimulating that same pituitary, in pulses, over minutes. Whether intermittent injections overcome that suppression enough to matter is untested.
Why the market moved
hCG's regulatory record changed in 2020 and gonadorelin's did not. On 2020-03-23, hCG and a handful of other protein products transitioned from drug approvals to biologics licences, and FDA's notice to compounders states that from that date they "will not be eligible for the exemptions for compounded drugs under sections 503A and 503B". Branded and generic hCG remained available on prescription; compounded hCG did not. Gonadorelin, a ten-residue peptide, stayed outside that change. The record documents the regulatory move; it says nothing about which molecule works better, and the substitution that followed was a supply decision, not the result of a trial. How compounding status works more generally is on our 503A vs 503B page.
What each label, and the lack of one, says
hCG's labels are old and candid. Pregnyl's dosage section introduces its regimens with "the following regimens have been advocated by various authorities", and for males with hypogonadotropic hypogonadism lists schedules starting at 500 to 1,000 units three times a week. Pregnyl's label also opens its indications with a warning in capitals that hCG "has not been demonstrated to be effective adjunctive therapy in the treatment of obesity" — the remnant of a different market.
Gonadorelin has no current human label to say anything. The five current US labels are veterinary — one, Cystorelin, states in its warnings section "Not for use in humans" —, and the discontinued human products left no current label behind. Any figure offered for gonadorelin with testosterone therapy is a clinic or protocol figure with no label, trial or indexed study behind it; where the published pulse figures come from is set out on the dosage page.
What the record does not contain
A randomised comparison of the two in adult men; any study of gonadorelin given alongside testosterone; any study of once- or twice-daily gonadorelin injections against the pump; any data on FSH-dependent outcomes with hCG alone on testosterone beyond one small series; and any published analysis of what research-market or compounded gonadorelin vials contain. Both are fertility and hormone questions with individual answers: anyone weighing either, or planning fertility while on testosterone, should take it to a urologist or endocrinologist.
Sources and dates
Read 2026-09-27: Gong et al. 2015 and Hsieh et al. 2013 abstracts (PubMed efetch); a PubMed esearch for gonadorelin/pulsatile GnRH with testosterone therapy and testicular outcomes (10 records, titles read) and for gonadorelin in title/abstract (296); the Pregnyl label (effective 2025-12-02) indications and dosage sections and the Ovidrel label (effective 2023-12-26) pharmacokinetics table, via the openFDA label endpoint. Gonadorelin product statuses, veterinary labels and the Handelsman 1984 route comparison are as read and cited on our gonadorelin dosage page (2026-09-21); the 2020 compounding notice as read for our hCG side-effects page (2026-09-26). Corrections go to the contact page.