Gonadorelin
GnRH, LHRH, Factrel, Lutrepulse
The hypothalamic hormone itself, with a four minute half-life that makes its popular use alongside testosterone pharmacologically odd.
Human trials
Previously FDA-approved as Factrel for diagnostic use and as Lutrepulse for pulsatile therapy; both were discontinued in the United States. Currently supplied by compounding pharmacies. Pulsatile GnRH remains in clinical use in Europe and elsewhere.
What it is
Gonadorelin is synthetic gonadotropin releasing hormone, the ten amino acid signal the hypothalamus sends to the pituitary to release LH and FSH. It sits one step above everything else in this part of the site: GnRH tells the pituitary to make LH, LH tells the testes to make testosterone, and hCG is a drug that imitates LH further down the same chain.
The pulsatility requirement is not a detail
GnRH only works in pulses. This is one of the more elegant facts in endocrinology and one of the most consequential.
Delivered every 60 to 120 minutes, GnRH sustains gonadotropin release and restores fertility in people whose hypothalamic signal is absent. Delivered continuously, the same molecule desensitises the pituitary and shuts gonadotropin release down. That is not a failure mode, it is a therapy: continuous GnRH agonists are used deliberately to suppress the axis in prostate cancer and endometriosis.
The same compound does opposite things depending on the rhythm of delivery.
Where the evidence actually is
Pulsatile GnRH by pump has good trial support in congenital hypogonadotropic hypogonadism and functional hypothalamic amenorrhoea, including recent comparisons against combined gonadotropin therapy for restoring spermatogenesis. That is real, replicated clinical evidence.
It is also evidence about a pump delivering a dose every ninety minutes, around the clock, for months.
The popular use does not match the evidence
Gonadorelin has become widely used alongside testosterone replacement as an alternative to hCG, largely because it remained available through compounding pharmacies during periods when hCG did not.
The pharmacological problem is straightforward. Its half-life is roughly four minutes. Two or three subcutaneous injections a week produce a handful of brief pituitary stimulations and nothing resembling the pulsatile pattern the trials used. Meanwhile the pituitary in someone on exogenous testosterone is already suppressed, which is the step gonadorelin is trying to act on.
hCG bypasses this entirely by acting at the testes, which is why its evidence for fertility preservation during testosterone therapy is direct and measurable and gonadorelin's is not.
Practical notes
- The delivery method is the therapy. Any claim about gonadorelin that does not specify pulse frequency is not describing the studied intervention.
- It is not a documented substitute for hCG in this context. They act at different levels of the axis, and only one of them has trial data for maintaining intratesticular testosterone during testosterone replacement.
- Availability drove adoption, not evidence. That is worth knowing when weighing the confident protocols written about it.
Side effects and warning signs
Commonly reported
- Injection-site reactions
- Headache
- Nausea
- Flushing
- Paradoxical suppression of gonadotropins if exposure is continuous rather than pulsatile
Stop and get medical help
- Signs of a thromboembolic event, reported with gonadotropin therapy generally
- Testicular shrinkage continuing despite treatment, which suggests the regimen is not achieving what it is meant to
Sources
From the community
Discussion for this compound concentrates in r/Testosterone and r/trt.
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