What it is
Triptorelin is gonadotropin-releasing hormone with one amino acid changed. Natural GnRH has glycine at position 6; triptorelin has D-tryptophan there. That single swap makes the molecule resist the enzymes that break the natural hormone down within minutes, and makes it bind the pituitary's GnRH receptor far more tightly.
The Trelstar label puts a number on the second point: in cultured rat pituitary cells, triptorelin was 100-fold more active than native GnRH at releasing luteinizing hormone, and 20-fold more active at displacing it from its receptor.
It is ten amino acids long, and it is an approved prescription medicine — one of the few entries in this library with current US approvals.
Two approvals, one effect: switching hormones off
Drugs@FDA holds four applications, all marketed (openFDA query, 2026-09-17):
| Product | Application | Sponsor | Strength | First approved |
|---|---|---|---|---|
| TRELSTAR | NDA 020715 | Verity | 3.75 mg per vial | 2000-06-15 |
| TRELSTAR | NDA 021288 | Verity | 11.25 mg per vial | 2001-06-29 |
| TRELSTAR | NDA 022437 | Verity | 22.5 mg per vial | 2010-03-10 |
| TRIPTODUR KIT | NDA 208956 | Azurity | 22.5 mg per vial | 2017-06-29 |
Trelstar is for advanced prostate cancer. The label's pivotal study randomised 277 men to Trelstar 3.75 mg or another approved GnRH agonist, monthly for nine months. On Trelstar, 125 of 137 (91.2%) reached castration-level testosterone — 50 ng/dL or less — by day 29, and 96.2% held that level from day 57 through day 253.
Triptodur is for central precocious puberty in children aged 2 and older. Its evidence is thinner in design: a single-arm, open-label study of 44 children, with no comparison group. Across 12 months, 93% to 98% had LH at prepubertal levels after a stimulation test, and 95% showed no advance in bone age relative to chronological age.
Both uses want the same thing: less sex hormone.
Why a hormone copy suppresses the hormone
The pituitary responds to GnRH only when it arrives in pulses. This is the same fact at the centre of the entry on unmodified GnRH, seen from the other side.
A long-acting analogue that is present all the time does two things in sequence:
- A surge. For the first days to weeks, LH, FSH and testosterone or oestrogen rise above baseline. Trelstar's label calls this tumor flare and warns it can worsen prostate cancer symptoms; Triptodur's label warns of a temporary increase in the signs of puberty in the first 2–4 weeks.
- Shutdown. The receptor desensitises and the axis goes quiet. Trelstar's label measured this: at days 85 and 169, 124 of 126 evaluable men (98.4%) had LH at or below 1.0 IU/L two hours after a repeat injection — the pituitary had stopped answering.
So the label effect of triptorelin is the opposite of what its resemblance to GnRH suggests. That is not a paradox; it is the design.
The dose figures on the labels
As printed on the US labels (read 2026-09-17), and describing those long-acting products only:
| Product | Dose | Interval | Route |
|---|---|---|---|
| Trelstar | 3.75 mg | every 4 weeks | intramuscular, under a physician's supervision |
| Trelstar | 11.25 mg | every 12 weeks | intramuscular |
| Trelstar | 22.5 mg | every 24 weeks | intramuscular |
| Triptodur | 22.5 mg | every 24 weeks | intramuscular, by a healthcare provider only |
Trelstar's label adds that the strengths are not additive: each is a different polymer formulation with its own release rate. The microgranules are poly-lactide-co-glycolide (138–183 mg per vial), which is why a single injection lasts months. None of these figures describes a short-acting vial of triptorelin sold outside the prescription channel, which is a different product with no label.
The use the labels do not cover
Triptorelin also circulates in bodybuilding forums as a way to restart natural testosterone production after an anabolic steroid cycle. The reasoning leans entirely on step 1 above — the surge — and assumes the surge can be had without step 2.
Neither US label covers that use, and neither label's trials studied it. What both labels document in detail is suppression with sustained exposure. A claim built on the drug's side effect in the first weeks is not supported by evidence about its main effect.
Safety, as the labels state it
Trelstar's label lists hypersensitivity including anaphylactic shock and angioedema; tumor flare; metabolic changes — raised blood sugar, diabetes, raised lipids and fatty liver disease; an increased risk of myocardial infarction, sudden cardiac death and stroke in men; convulsions; and severe cutaneous adverse reactions.
Triptodur's label adds psychiatric events in children — emotional lability, crying, irritability, anger and aggression — and pseudotumor cerebri (raised pressure inside the skull), with headache and blurred vision as warning signs.
Where it stands
A well-characterised, currently approved drug with a large literature: PubMed indexes 2,470 triptorelin records, 338 of them randomized controlled trials (E-utilities, 2026-09-17). The approved evidence is about suppression. The online use is about stimulation, and has no label behind it.
Related entries in this library: gonadorelin, the unmodified releasing hormone, explains the pulse rule; the kisspeptin signal sits one step further upstream; hCG is the other hormone discussed for the same post-cycle purpose.
Last checked
2026-09-17. Drugs@FDA records for NDA 020715, 021288, 022437 and 208956 and the current Trelstar and Triptodur labels were read through the openFDA API on that date, as were the PubMed counts.