What it is
Gonadorelin is a synthetic form of native gonadotropin-releasing hormone (GnRH), the decapeptide the hypothalamus releases in pulses roughly every 60 to 120 minutes to drive pituitary LH and FSH secretion. It has been an FDA-approved drug since the 1970s-80s, historically marketed as Factrel for diagnostic pituitary function testing and as Lutrepulse, delivered by a dedicated pulsatile infusion pump, for inducing ovulation in women with hypothalamic amenorrhea. Lutrepulse has since been discontinued in the US; the diagnostic use persists.
Native GnRH, and gonadorelin as its synthetic copy, has a plasma half-life of only a few minutes. Its physiological effect depends entirely on pulsatile delivery: continuous, non-pulsatile exposure to GnRH or its agonists does not sustain LH/FSH release and instead downregulates the pituitary receptor, which is the exact mechanism GnRH agonist drugs like triptorelin exploit for suppression rather than stimulation.
How it is actually used off-label now
Outside its original approved uses, gonadorelin is now widely used off-label in testosterone replacement therapy protocols, given by intermittent subcutaneous injection two to three times per week, intended to keep the hypothalamic-pituitary-gonadal axis and testicular function active during exogenous testosterone administration. This specific off-label protocol, periodic subcutaneous gonadorelin during TRT, does not have a dedicated randomized, placebo-controlled trial establishing its efficacy for preserving fertility or testicular size in the sources reviewed for this entry; the rationale is drawn from GnRH physiology rather than a trial of this specific regimen.
This is a meaningful pharmacological mismatch worth stating plainly: the hormone’s entire mechanism depends on a pulse roughly every one to two hours, and a subcutaneous injection two or three times a week does not reproduce that pattern. Whether an intermittent, widely spaced injection meaningfully activates the same pathway a physiological GnRH pulse generator does is not established by a trial designed to test it.
What is not known
Whether gonadorelin given two to three times weekly by subcutaneous injection, the common off-label TRT-adjunct protocol, preserves fertility or testicular function as intended. No dedicated randomized trial of this specific regimen was located.
Long-term outcomes, including sperm parameters and testicular volume, from this off-label use pattern specifically, as distinct from the original approved pulsatile-pump indication.