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approvedHormone Regulation

Triptorelin

Also known as: Trelstar, Decapeptyl, Diphereline, Gonapeptyl, Triptorelin Pamoate

Triptorelin is a synthetic GnRH agonist decapeptide FDA-approved for the palliative treatment of advanced prostate cancer and central precocious puberty. Like other GnRH agonists, it produces an initial stimulatory flare followed by profound suppression of the hypothalamic-pituitary-gonadal axis, achieving medical castration. Available in 1-month, 3-month, and 6-month depot formulations, triptorelin is one of the most widely used GnRH agonists globally. It is also extensively used in Europe and internationally for endometriosis, IVF protocols, and as part of gender-affirming hormone therapy.

3 cited references·5 researched benefits

Quick Answer

Triptorelin (Trelstar) is a GnRH agonist decapeptide that suppresses sex hormones by downregulating pituitary GnRH receptors. FDA-approved for advanced prostate cancer and central precocious puberty, it is available in depot injections lasting 1-6 months. It achieves castrate testosterone levels within 2-4 weeks, making it a standard hormonal therapy for hormone-sensitive prostate cancer and a widely used agent in reproductive endocrinology.

Key Facts

Mechanism
Triptorelin binds to GnRH receptors on pituitary gonadotroph cells with approximately 100 times the potency of native GnRH. It contains a D-tryptophan substitution at position 6 that confers resistance to enzymatic degradation. Initial administration produces a surge of LH, FSH, and downstream sex steroids (the flare effect). Continuous receptor occupancy over 1-3 weeks leads to receptor downregulation and desensitization, resulting in suppression of LH and FSH to castrate levels. In men, testosterone falls below 50 ng/dL (the castrate threshold); in women, estradiol decreases to postmenopausal levels. Depot formulations use polylactide-coglycolide microspheres for sustained release.
Research Status
approved
Half-Life
~3-5 hours (depot formulations provide sustained release over 1-6 months)
Molecular Formula
C₆₄H₈₂N₁₈O₁₃
Primary Use
Hormone Regulation
Table of Contents

Benefits

  • Reduces testosterone to castrate levels in advanced prostate cancer — equivalent efficacy to orchiectomy with large-scale trial evidencestrong
  • Controls central precocious puberty — halts pubertal progression and restores age-appropriate growth patterns in childrenstrong
  • Treats endometriosis-associated pain (widely used internationally) — significant reduction in endometriotic lesions and pelvic pain symptomsstrong
  • Prevents premature LH surge in IVF protocols — used extensively in European ART centers for controlled ovarian stimulationstrong
  • Extended depot formulations (6-month) improve patient compliance and reduce injection frequency compared to monthly formulationsstrong

Dosage Protocols

RouteDosage RangeFrequencyNotes
Intramuscular depot injection (prostate cancer)3.75 mg (1-month), 11.25 mg (3-month), or 22.5 mg (6-month)Per depot intervalTrelstar formulations. Antiandrogen flare protection recommended for first 2-4 weeks. Monitor testosterone levels to confirm castrate suppression.
Intramuscular depot injection (precocious puberty)22.5 mg every 6 months (Triptodur)Every 6 monthsTriptodur is a 6-month depot specifically approved for central precocious puberty in children aged 2 years and older. Dose is not weight-based.
Intramuscular injection (endometriosis, international)3.75 mg monthly or 11.25 mg every 3 monthsMonthly or every 3 months for up to 6 monthsWidely used outside the US (Decapeptyl). Add-back hormonal therapy recommended to mitigate bone loss and vasomotor symptoms.

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Hot flashes — the most frequently reported side effect, occurring in 50-75% of patients due to sex hormone withdrawalcommon
  • Skeletal pain and tumor flare — initial worsening of cancer symptoms during the first 1-2 weeks due to testosterone surge; requires antiandrogen coverserious
  • Decreased bone mineral density — progressive bone loss with prolonged therapy; risk of osteoporosis and fracturesserious
  • Injection site reactions — pain, erythema, and induration at the intramuscular depot injection sitecommon
  • Erectile dysfunction and decreased libido — expected pharmacologic effect of castrate testosterone levelscommon
  • Mood disturbances and depression — reported in 5-10% of patients; may be related to sex hormone suppressioncommon
  • Increased risk of metabolic syndrome and cardiovascular events with long-term androgen deprivation — weight gain, insulin resistance, and lipid changesserious

Frequently Asked Questions

What is the difference between triptorelin and leuprolide?
Both are GnRH agonists with similar mechanisms and efficacy. The main differences are in their amino acid sequences (triptorelin has a D-tryptophan substitution vs. D-leucine in leuprolide), available depot formulations, and geographic usage patterns. Triptorelin is more commonly used in Europe, while leuprolide dominates the US market. Clinical efficacy for prostate cancer suppression is considered equivalent. Triptorelin has a slightly longer half-life (3-5 hours vs. 3 hours) and the Triptodur formulation offers a convenient 6-month dosing interval for precocious puberty.
Does triptorelin cause an initial testosterone flare?
Yes. Like all GnRH agonists, triptorelin initially stimulates LH and testosterone release for approximately 1-2 weeks before receptor downregulation causes suppression. This testosterone flare can temporarily worsen prostate cancer symptoms including bone pain, urinary obstruction, and rarely spinal cord compression. Antiandrogen therapy (e.g., bicalutamide) should be started before or concurrently with the first injection and continued for 2-4 weeks to block the effects of the flare. GnRH antagonists like degarelix avoid this flare entirely.
How quickly does triptorelin achieve castrate testosterone levels?
After the initial flare period, testosterone levels begin declining by the end of week 2 and typically reach castrate levels (below 50 ng/dL) by 3-4 weeks. The 3-month depot formulation maintains castrate levels throughout the dosing interval in over 95% of patients. Testosterone levels should be monitored at 3-6 months to confirm adequate suppression, as a small percentage of patients may experience incomplete suppression or testosterone escape.
Is triptorelin used in gender-affirming care?
Yes. Triptorelin (particularly as Decapeptyl in Europe) is one of the most commonly used puberty blockers in gender-affirming care for transgender adolescents with gender dysphoria. It temporarily suppresses puberty to allow time for psychological assessment and decision-making. The effects are reversible upon discontinuation — puberty resumes if treatment is stopped. Major endocrine societies, including the Endocrine Society, include GnRH agonists like triptorelin in their clinical guidelines for gender-dysphoric youth.
What monitoring is needed during triptorelin therapy?
For prostate cancer: testosterone levels at 1, 3, and 6 months to confirm castrate suppression, PSA monitoring every 3-6 months, and periodic DEXA bone density scans. For precocious puberty: LH, FSH, and sex steroid levels, growth velocity, bone age radiographs, and Tanner staging. For all patients on long-term therapy: metabolic monitoring including fasting glucose, lipids, and HbA1c due to increased metabolic syndrome risk. Bone density monitoring is especially important for treatment durations exceeding 6 months.

References

  1. 1
    GnRH agonists and antagonists in the treatment of prostate cancer(2004)PubMed ↗
  2. 2
    Central precocious puberty: treatment with GnRH agonists including triptorelin and long-term outcome(2009)PubMed ↗
  3. 3
    Triptorelin in the treatment of advanced prostate cancer: a systematic review(2010)PubMed ↗

Latest Research

Last updated: 2026-02-19