Triptorelin
A long-acting GnRH agonist given every one, three or six months
Triptorelin shuts down sex-hormone production the way other GnRH agonists do, but its depot formulations stretch dosing to as long as six months. Approved for advanced prostate cancer, it is also used in central precocious puberty and in breast cancer.
What is it?
Continuous GnRH stimulation desensitises the pituitary, so LH and FSH fall and with them testosterone or oestrogen. Triptorelin, a synthetic decapeptide GnRH agonist, is built for duration: the Trelstar label offers 3.75 mg every four weeks, 11.25 mg every twelve and 22.5 mg every twenty-four, each as a single intramuscular injection into either buttock, and warns that the strengths are not additive and must be chosen for the intended interval. Like every agonist it first raises testosterone, and the label warns that prostate cancer symptoms such as bone pain, urinary obstruction or nerve compression can briefly worsen in the first weeks.
In advanced prostate cancer it was compared directly with leuprolide in 284 men. Triptorelin lowered testosterone more slowly, so fewer men were at castrate levels on day 29 (91.2% against 99.3%), but by day 57 the rates were equal (97.7% against 97.1%), maintenance from day 29 to day 253 was equivalent, and nine-month survival, a secondary endpoint, was higher on triptorelin (97.0% against 90.5%). A later comparison of three agonists in 125 men found all three reached the usual castration thresholds, but triptorelin gave the lowest mean testosterone and the highest rate below 10 ng/dL (93.2%, against 86.4% for leuprolide and 54.2% for goserelin).
In premenopausal breast cancer it is the ovarian-suppression half of the treatment. The HOBOE phase 3 trial gave all women triptorelin and compared what was added: at a median 9.2 years, letrozole with or without zoledronic acid improved disease-free survival over tamoxifen (hazard ratios 0.58 and 0.69), with no significant difference in overall survival.
In children with central precocious puberty, trials have tested how long an injection can hold. A six-month formulation in 66 Chinese children suppressed LH in all of them at month 6 and in 98.5% at month 12, with growth velocity slowing from 9.8 to about 5 cm a year and breast development stable or reduced in most girls. A three-month 11.25 mg formulation in 37 children suppressed the LH response in 83.8% at three months and 86.5% at six.
In endometriosis, a three-month formulation was non-inferior to the one-month form in Chinese women, with over 98% chemically castrated at week 12 and similar relief of pelvic pain. In IVF, a long triptorelin protocol was the reference against which the antagonist ganirelix was tested: triptorelin ran 26 days against 9, ongoing pregnancy per attempt was 33.9% against 31.0%, and local skin reactions were twice as common (24.1% against 11.9%).
After an intramuscular injection, triptorelin peaks within one to three hours and does not accumulate over nine to twelve months of treatment; given intravenously its half-lives are about 6 minutes, 45 minutes and 3 hours. It is unlikely to involve liver CYP450 enzymes, no formal interaction studies have been done, and the label advises against drugs that raise prolactin, which reduces pituitary GnRH receptors. Its warnings follow from castration: metabolic changes, cardiovascular disease, QT prolongation, convulsions, severe skin reactions and harm in pregnancy.
Mechanism of Action
Triptorelin is a GnRH agonist: after an initial surge, continuous stimulation desensitises the pituitary and LH, FSH and sex hormones fall.
Initial flare
Testosterone rises first, which is why the label warns of tumour flare in the first weeks.
Then suppression
Desensitised pituitary output brings testosterone to castrate levels, equal to leuprolide by day 57 in the head-to-head trial.
Depot duration
Peaks 1 to 3 hours after injection and does not accumulate over 9 to 12 months, with formulations lasting 4, 12 or 24 weeks (label).
Published Research
The studies behind triptorelin, read from their PubMed abstracts: prostate cancer comparisons, breast cancer, precocious puberty, endometriosis and IVF.
Against leuprolide in 284 men
Castrate testosterone at day 29 was 91.2% on triptorelin against 99.3% on leuprolide, equal by day 57 (97.7% against 97.1%); maintenance was equivalent and nine-month survival 97.0% against 90.5%.
Three agonists compared, 125 men
All reached castration at 50 or 20 ng/dL; triptorelin gave the lowest mean testosterone and the highest rate below 10 ng/dL (93.2%, against 86.4% leuprolide and 54.2% goserelin).
Ten years on, in breast cancer
At a median 9.2 years, letrozole plus zoledronic acid (HR 0.58) and letrozole alone (HR 0.69) improved disease-free survival over tamoxifen, all with triptorelin; overall survival did not differ significantly.
A six-month injection in children
In 66 children, LH was suppressed in all at month 6 and in 98.5% at month 12; growth velocity fell from 9.82 to 5.17 cm/year and sex hormones stayed at prepubertal levels.
The three-month formulation
In 37 children with central precocious puberty, 11.25 mg every three months suppressed the LH response in 83.8% at three months and 86.5% at six, with mild to moderate adverse events.
Two formulations in endometriosis
The three-month pamoate formulation was non-inferior to the one-month acetate form: over 98% of women were chemically castrated at week 12, with similar pain relief.
Against a GnRH antagonist in IVF
Against 236 women on ganirelix, the 119 on a long triptorelin protocol had a 26-day versus 9-day regimen, ongoing pregnancy of 33.9% against 31.0% per attempt, and more local skin reactions (24.1% against 11.9%).
Dosing Data
Trelstar is a single intramuscular injection into the buttock at an interval set by the strength.
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Side Effects & Contraindications
Reported Side Effects
From the Trelstar prescribing information (DailyMed set b1b84d62, version 20, effective June 30, 2026) and the trials.
Contraindications & Cautions
From the label.
Legal Status
Approved and in long-standing use.
Frequently Asked Questions
?How often is triptorelin given?
The label offers 3.75 mg every four weeks, 11.25 mg every twelve or 22.5 mg every twenty-four, by intramuscular injection, with the strengths not interchangeable.
?What is it approved for in the US?
Advanced prostate cancer under Trelstar; a separate product is approved for central precocious puberty.
?Does it work for precocious puberty?
Trials of three-month and six-month formulations found effects maintained through the dosing interval, with no child stopping for side effects in the six-month trial.
?What does it do in breast cancer?
It suppresses ovarian function in premenopausal women; the HOBOE trial's ten-year update compared what is added to it, favouring letrozole over tamoxifen on disease-free survival.
?How does it compare with leuprolide?
In a 284-man trial it reached castrate testosterone more slowly but matched leuprolide from day 57 on; a smaller study found it lowered testosterone furthest of three agonists.
?Why can symptoms get worse at first?
Like all GnRH agonists it briefly raises testosterone before suppressing it, and the label warns this can worsen bone pain or urinary symptoms in the first weeks.
?Does it interact with other drugs?
No formal studies exist; the label advises against drugs that raise prolactin, and triptorelin is unlikely to involve liver CYP450 enzymes.
?Is it used in endometriosis or IVF?
Outside the US label, yes: a three-month form matched the monthly one in endometriosis, and long triptorelin protocols were the reference in IVF antagonist trials.
References
- [fda-pi] Trelstar (triptorelin pamoate) prescribing information, sections 1 and 2 (DailyMed SPL version 20, effective June 30, 2026; read October 1, 2026).
- [pubmed] Heyns CF, et al. "Comparative efficacy of triptorelin pamoate and leuprolide acetate in men with advanced prostate cancer." BJU Int, 2003;92(3):226-31. PMID: 12887472.
- [pubmed] Shim M, et al. "Effectiveness of three different luteinizing hormone-releasing hormone agonists in the chemical castration of patients with prostate cancer: Goserelin versus triptorelin versus leuprolide." Investig Clin Urol, 2019;60(4):244-250. PMID: 31294133.
- [pubmed] Gravina A, et al. "Ten-year update of HOBOE phase III trial comparing triptorelin plus either tamoxifen or letrozole or zoledronic acid + letrozole in premenopausal hormone receptor-positive early breast cancer patients." ESMO Open, 2025;10(1):104085. PMID: 39754976.
- [pubmed] Yu X, et al. "A Phase 3, Open-Label, Single-Arm Trial of the Efficacy and Safety of Triptorelin 6-Month Formulation in Chinese Children with Central Precocious Puberty." Adv Ther, 2024;41(12):4537-4556. PMID: 39412628.
- [pubmed] Zenaty D, et al. "A 6-Month Trial of the Efficacy and Safety of Triptorelin Pamoate (11.25 mg) Every 3 Months in Children with Precocious Puberty: A Retrospective Comparison with Triptorelin Acetate." Horm Res Paediatr, 2016;86(3):188-195. PMID: 27603324.
- [pubmed] Li X, et al. "Assessment of Two Formulations of Triptorelin in Chinese Patients with Endometriosis: A Phase 3, Randomized Controlled Trial." Adv Ther, 2022;39(10):4663-4677. PMID: 35947347.
- [pubmed] "Comparable clinical outcome using the GnRH antagonist ganirelix or a long protocol of the GnRH agonist triptorelin for the prevention of premature LH surges in women undergoing ovarian stimulation." Hum Reprod, 2001;16(4):644-51. PMID: 11278211.
- [pubmed] Klotz L, et al. "The efficacy and safety of degarelix: a 12-month, comparative, randomized, open-label, parallel-group phase III study in patients with prostate cancer." BJU Int, 2008;102(11):1531-8. PMID: 19035858.
- [fda-pi] Triptodur (triptorelin) Prescribing Information. Azurity Pharmaceuticals.
Sources & Citations
Studies were read from their PubMed records (October 6, 2026); the labels and Drugs@FDA are listed below with their read dates.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.