What Is Triptorelin?

1. What is triptorelin, and how does the flare-then-shutdown mechanism work?

Natural GnRH is a decapeptide (10 amino acids) that enzymes rapidly cleave at position 6. Triptorelin keeps the 10-amino-acid backbone of natural GnRH but substitutes D-tryptophan for L-glycine at position 6. According to the Trelstar prescribing information, the pamoate salt has an empirical formula of C64H82N18O13 · C23H16O6 and a molecular weight of 1,699.9 g/mol. For background on why peptides require injection, see the peptide overview.

In preclinical studies summarized in the Trelstar label, triptorelin was 100-fold more active than native GnRH at stimulating LH release from rat pituitary cells in culture and 20-fold more active at displacing radiolabeled GnRH from pituitary receptors. In animal tests, triptorelin pamoate had 13-fold higher LH-releasing activity and 21-fold higher FSH-releasing activity than native GnRH.

Because the pituitary needs intermittent pulses to stay sensitive, continuous stimulation unfolds in two stages:

• Initial flare (Days 1 to 14). Right after the first injection, triptorelin stimulates pituitary GnRH receptors, driving a sharp rise in LH and FSH. In men, serum testosterone climbs above baseline, peaking on Day 4 after the 3.75 mg depot and on Days 2 to 3 after the 11.25 mg and 22.5 mg depots (Trelstar label). In girls and women, estradiol rises briefly, which can cause temporary pubertal signs or vaginal spotting (Triptodur label).
• Receptor downregulation and shutdown (Weeks 2 to 4 onward). Constant receptor occupation desensitizes pituitary gonadotroph cells and reduces receptor synthesis. LH and FSH fall, and by Weeks 2 to 4 serum testosterone in men drops into the surgical castration range—50 ng/dL (1.735 nmol/L) or below—where it stays for as long as depot treatment continues (Trelstar label; Merseburger and Hupe, 2016).

A population pharmacokinetic/pharmacodynamic model of 8 healthy volunteers and 74 prostate cancer patients estimated a receptor dissociation constant of 0.931 ng/mL and showed that holding serum triptorelin at or above 0.0609 ng/mL kept 95% of men castrated (Romero et al., 2012).

2. What indications, brands and doses are approved?

Long-acting triptorelin depots incorporate the peptide into biodegradable microgranules of poly(D,L-lactide-co-glycolide), or PLGA (Trelstar label; Triptodur label). Each US product is mixed with 2 mL of sterile water and injected intramuscularly into the buttock by a clinician.

The Trelstar label notes that the three strengths contain different PLGA amounts (138 mg, 120 mg and 183 mg) and release drug at different rates. Strengths are not additive, and the reconstituted suspension must be injected within less than 2 minutes to avoid thickening.

European and UK approvals: Decapeptyl SR

In the UK and European Union, Ipsen markets sustained-release triptorelin as Decapeptyl SR (and in some countries as Pamorelin, Diphereline or Gonapeptyl) with broader indications across strengths:

Daily 0.1 mg subcutaneous injections are also used in Europe for pituitary downregulation during in-vitro fertilization (IVF) cycles.

3. Pharmacokinetics: how long does triptorelin stay in the body?

After a 0.5 mg intravenous bolus in 6 healthy young men (aged 20 to 22 years), triptorelin followed a three-compartment model with half-lives of about 6 minutes, 45 minutes and a terminal elimination half-life of 2.81 hours (Trelstar label). Volume of distribution was 30 to 33 L, with no evidence of plasma protein binding.

Triptorelin is cleared by both the liver and kidneys without cytochrome P450 metabolism. In vitro studies in the Triptodur label showed no inhibition of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 or 3A4/5, no induction of CYP1A2 or 3A4/5, and no P-glycoprotein inhibition. However, kidney or liver disease slows clearance and increases exposure (AUC) 2- to 4-fold (Trelstar label):

Intramuscular depots release drug in an early burst followed by a maintenance plateau:

• Men with prostate cancer: After a single injection of 3.75 mg, 11.25 mg or 22.5 mg Trelstar, mean Cmax reached 28.4 ng/mL, 38.5 ng/mL and 44.1 ng/mL at 1 to 3 hours, with no accumulation over 9 to 12 months (Trelstar label). In 14 men given the 11.25 mg 3-month depot, plasma triptorelin peaked at 35.70 ng/mL at 2.5 hours, rose slightly around Day 24 (0.32 ng/mL), and held a mean plateau of 0.06 ng/mL through Day 91 (Bouchot et al., 1998).
• Children with CPP: After two 22.5 mg Triptodur injections 24 weeks apart in 44 children aged 2 to 9 years, geometric mean Cmax at 4 hours was 39.9 and 36.5 ng/mL, followed by geometric mean levels of 0.11, 0.17, 0.05 and 0.03 ng/mL at Months 1, 2, 3 and 6 (Triptodur label).

Because polymer breakdown sets the duration, a simple half-life calculator built on the 2.81-hour figure does not apply to depot injections.

4. What do the clinical trials show in prostate cancer?

Androgen deprivation therapy (ADT) aims to lower testosterone to surgical castration levels (50 ng/dL or below, with many clinicians also tracking a stricter 20 ng/dL threshold).

Pivotal US trials across the 1-, 3- and 6-month depots

The three US registration trials measured castration at Day 29 and maintenance from Day 57 through the end of follow-up (Trelstar label; Heyns et al., 2003; Lundström et al., 2009).

In the 6-month study (Lundström et al., 2009), median prostate-specific antigen (PSA) fell by 97% at 6 months and 96% at 12 months. Across pooled 1-, 3- and 6-month trials, more than 90% of patients also achieved the stricter testosterone threshold below 20 ng/dL at 6, 9 and 12 months (Merseburger and Hupe, 2016).

Comparisons with leuprolide, surgical castration and subcutaneous dosing

• Triptorelin vs leuprolide: Heyns and colleagues (2003) randomized 284 men with advanced prostate cancer to 9 monthly injections of triptorelin 3.75 mg (n = 140) or leuprolide 7.5 mg (n = 144). Castration was slightly lower on triptorelin at Day 29 (91.2% vs 99.3%; difference −8.0%, 95% CI −16.9% to −1.4%) but equivalent by Day 57 (97.7% vs 97.1%). Cumulative maintenance from Day 29 to Day 253 was 96.2% vs 91.2% (mean maintenance 98.8% vs 97.3%), median PSA on triptorelin fell from 46.8 to 1.3 ng/mL, and 9-month survival was 97.0% vs 90.5% (P = 0.033).
• Three-month vs 28-day depot: Teillac and colleagues (2004) randomized 131 patients to one 3-month depot (n = 63) or three 28-day injections (n = 68). Day 84 castration rates were 98% and 96%, median time to castration was 18.8 vs 18.5 days (P = 0.86), and mean PSA fell 91.0% vs 91.7% (P = 0.73).
• Triptorelin vs surgical castration: Botto and colleagues (2007) randomized 80 untreated patients to monthly triptorelin (n = 40) or bilateral pulpectomy (n = 40). At 1 month, 35 of 40 and 38 of 40 men were castrated; median survival was 37.5 vs 33 months, with equivalent 3-year cancer-specific survival.
• Subcutaneous 3-month depot and urinary symptoms: In 126 men given subcutaneous triptorelin pamoate 11.25 mg at baseline and Week 13, 97.6% (123/126) were castrated at Week 4 (median 22 days), 96.6% (115/119) maintained castration at Week 26, 90.0% stayed below 20 ng/dL, and median PSA dropped 96.0% (Lebret et al., 2015). In a 6-country observational study of 2,461 men starting 1- or 3-month triptorelin (1,282 with moderate-to-severe lower urinary tract symptoms, IPSS above 7), mean IPSS fell from 18.2 to 11.9 at Week 24 and 10.6 at Week 48 (P below 0.001), while mean PSA fell from 117.9 to 16.6 ng/mL (Merseburger and Hupe, 2016).

5. What do the clinical trials show in central precocious puberty?

Central precocious puberty (CPP) is early activation of the hypothalamic-pituitary-gonadal axis, which accelerates bone maturation and closes growth plates prematurely. Continuous GnRH agonist therapy pauses puberty so children can grow toward their genetic target height.

The pivotal Triptodur 6-month trial

Triptodur (22.5 mg every 24 weeks) was evaluated in an open-label phase 3 trial of 44 treatment-naive children aged 2 to 9 years (39 girls, 5 boys; median age 8 years) across 18 centers in the US, Chile and Mexico (Klein et al., 2016; Triptodur label). Each child received two doses 24 weeks apart:

Forty-eight hours after the second injection, only 1 of 22 evaluated girls showed a brief hormone rise (Triptodur label).

Adult height and head-to-head CPP outcomes

• Long-term adult height: Heger, Partsch and Sippell (1999) followed 50 young women (mean age 16.7 years) treated with monthly depot triptorelin for an average of 4.4 years. Adult height reached 160.6 ± 8.0 cm, up from a pre-treatment predicted height of 154.9 ± 9.6 cm (genetic target 163.6 ± 6.2 cm), with 78% reaching their family target range and menarche occurring at 12.3 ± 1.4 years. In a Spanish registry of 465 girls treated with monthly triptorelin 3.75 mg (216 followed to adult height), final height averaged within 1.5 cm of target height (95% CI −2.56 to −0.45 cm; Corripio et al., 2024).
• Triptorelin vs leuprolide in CPP: In 110 Italian girls with idiopathic CPP treated with triptorelin (n = 62) or leuprolide (n = 48), Valenzise and colleagues (2023) found no significant difference in efficacy or tolerability (mild menopausal-like symptoms in 41.8% overall, P = 0.558).

6. Side effects, bone mineral density and metabolic risks

Neither US label carries a boxed warning, but both detail adverse reactions from the initial hormone surge and chronic sex-steroid suppression (Trelstar label; Triptodur label):

Bone mineral density

• Men on ADT: In men with stage C prostate cancer given triptorelin 3.75 mg every 4 weeks, lumbar spine and femoral neck bone mineral density (BMD) fell by 3.0% and 2.7% at Month 6, 4.6% and 3.9% at Month 12, and 7.1% and 6.6% at Month 18 (Maillefert et al., 1999).
• Women on gynecologic courses: The Decapeptyl SR 3 mg SmPC notes trabecular bone loss averaging about 1% per month over a 6-month endometriosis or fibroid course, largely reversing within 6 to 9 months after stopping.
• Children with CPP: In 48 girls on triptorelin randomized to receive 1 g/day of calcium (n = 27) or no supplement (n = 21) for at least 2 years, final adult BMD was in the normal range for both groups, and calcium supplementation produced significantly higher volumetric spine BMD at treatment end (0.213 vs 0.192 g/cm3, P below 0.01) and at final height (0.246 vs 0.227 g/cm3, P below 0.05; Antoniazzi et al., 2003). In the 50 women followed by Heger and colleagues (1999), adult lumbar spine BMD z-score averaged 0.0 ± 1.0.

Metabolic, cardiovascular and neurological warnings

• Diabetes, lipids and cardiovascular events: The Trelstar label warns of hyperglycemia, diabetes, hyperlipidemia, non-alcoholic fatty liver disease, myocardial infarction, sudden cardiac death, stroke and QTc interval prolongation. In a Medicare cohort of 73,196 men with locoregional prostate cancer (Keating et al., 2006), GnRH agonist therapy was associated with higher risks of incident diabetes (adjusted HR 1.44), coronary heart disease (HR 1.16), myocardial infarction (HR 1.11) and sudden cardiac death (HR 1.16).
• Tumor flare and pituitary apoplexy: The first-week testosterone surge can worsen bone pain, urinary obstruction or spinal cord compression in advanced prostate cancer. Post-marketing reports also describe rare pituitary apoplexy (bleeding or infarction of the pituitary, usually in patients with an undiagnosed pituitary adenoma) within hours to 2 weeks of the first dose (Trelstar label).
• Psychiatric symptoms, seizures, skin reactions and intracranial pressure: Both US labels warn of emotional lability (crying, irritability, anger, aggression), depression, convulsions, and severe cutaneous adverse reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS and AGEP). The Triptodur label adds pseudotumor cerebri (idiopathic intracranial hypertension) in children.
• Fertility and recovery: Triptorelin is contraindicated in pregnancy. While the pediatric label expects axis recovery within 6 to 12 months after stopping, older men treated long term for prostate cancer recover more slowly: among 307 men followed after an average of 17 months of ADT, 8% remained castrate at 24 months, 76% reached testosterone above 300 ng/dL, and 51% returned to baseline (Nascimento et al., 2019).

7. Triptorelin vs leuprolide and gonadorelin (and the “post-cycle” myth)

Peptide catalogs often list triptorelin alongside leuprolide, gonadorelin, hCG and kisspeptin-10, but their structures and schedules produce opposite hormonal results:

Why do forums claim a single 100 mcg dose “restarts” testosterone?

Unregulated peptide vendors sell 100 mcg vials of triptorelin with claims that a single shot restores testosterone after anabolic steroid cycles. That claim traces to a single case report by Pirola and colleagues (2010), in which one 34-year-old bodybuilder with hypogonadotropic hypogonadism after 10 years of steroid use received a diagnostic 100 mcg triptorelin test; his LH and FSH rose on the test day, and his serum testosterone was normal 1 month later.

Because a single case report has no untreated control group, it cannot distinguish a drug effect from spontaneous recovery after stopping steroids. Furthermore, because triptorelin is 100-fold more potent than native GnRH (Trelstar label), repeated or excessive dosing desensitizes the pituitary and suppresses testosterone rather than raising it. No controlled trial supports triptorelin for post-cycle therapy.

8. Legal, compounding and anti-doping (WADA) status

As of November 2026:

• US prescription and DEA status: Trelstar and Triptodur are prescription-only drugs administered by healthcare professionals and are not scheduled under the DEA’s Schedule III anabolic steroid list in 21 CFR 1308.13.
• Compounding (Sections 503A and 503B): Because triptorelin is a component of FDA-approved drugs, it meets the bulk-substance threshold under Section 503A (subject to restrictions against copying commercial drugs), whereas it does not appear on the Section 503B Bulks List for outsourcing facilities.
• WADA 2026 Prohibited List: The 2026 WADA Prohibited List bans triptorelin at all times in male athletes under section S2.2.1 (Testosterone-stimulating peptides in males) because of its acute stimulatory surge.

9. Relevance to people using GLP-1 medications

No randomized trial has tested triptorelin specifically alongside semaglutide or tirzepatide, and because triptorelin does not use cytochrome P450 enzymes (Triptodur label), direct metabolic drug interactions are not expected.

Clinically, however, GLP-1 receptor agonists are increasingly prescribed to prostate cancer patients who develop diabetes or cardiometabolic risk during ADT. In a 2026 TriNetX cohort study of men with type 2 diabetes and prostate cancer receiving ADT (Huang et al., 2026), propensity-score matching compared 659 patients per group for GLP-1 receptor agonists versus DPP-4 inhibitors and 1,009 per group for GLP-1 receptor agonists versus SGLT2 inhibitors. GLP-1 receptor agonist use was associated with lower all-cause mortality than DPP-4 inhibitors (HR 0.60, 95% CI 0.46–0.79), fewer major adverse kidney events (HR 0.63, 95% CI 0.48–0.81) and fewer thrombotic events (HR 0.53, 95% CI 0.32–0.89), as well as lower all-cause mortality than SGLT2 inhibitors (HR 0.76, 95% CI 0.59–0.99). Because both ADT and weight loss can reduce lean mass and bone density, patients on both classes should coordinate strength training, protein, calcium and lab monitoring with their clinicians (see GLP-1 and muscle loss).

10. What clinicians and patients monitor on triptorelin

For practical ways to keep depot dates and lab results organized alongside other medications, see the peptide tracker vs spreadsheet guide.

11. Triptorelin FAQ

• Does triptorelin increase or decrease testosterone?

  It does both in sequence, and its sustained medical effect is suppression. During the first week after an injection, triptorelin stimulates pituitary GnRH receptors and triggers a temporary surge in LH, FSH and testosterone, peaking around Days 2 to 4. With continuous release from a depot injection, pituitary receptors desensitize and testosterone drops to the surgical castration range (50 ng/dL or below) within 2 to 4 weeks.

• What is the difference between Trelstar, Triptodur and Decapeptyl?

  All three deliver triptorelin in biodegradable polymer microparticles for slow release, but they hold different approvals. In the US, Trelstar (3.75 mg every 4 weeks, 11.25 mg every 12 weeks, or 22.5 mg every 24 weeks) is FDA-approved for advanced prostate cancer, while Triptodur (22.5 mg every 24 weeks) is approved for children aged 2 years and older with central precocious puberty. Decapeptyl SR is the European and UK brand family, where selected strengths also carry approvals for endometriosis, uterine fibroids and premenopausal early breast cancer.

• How does triptorelin compare with leuprolide and gonadorelin?

  Gonadorelin is identical to natural 10-amino-acid GnRH, has an intravenous half-life of 2 to 3 minutes, and stimulates LH and FSH only when delivered in pulses every 1 to 2 hours. Triptorelin (a decapeptide with D-tryptophan at position 6) and leuprolide (a 9-amino-acid analog) are long-acting superagonists formulated into 1- to 6-month depots that shut the axis down. In a 284-man randomized trial, monthly triptorelin 3.75 mg and leuprolide 7.5 mg maintained castration at equivalent rates from Month 2 through Month 9 (96.2% vs 91.2%).

• Does a single 100 mcg dose of triptorelin restart testosterone after steroids?

  No controlled clinical trial has tested that protocol. Forum claims rely on a single 2010 case report of one 34-year-old man with steroid-induced hypogonadism who received a diagnostic 100 mcg triptorelin test and had normal testosterone a month later. Without a control group, a single case cannot show whether the injection caused recovery or coincided with spontaneous recovery.

• What are the main side effects of triptorelin?

  In US prostate cancer trials, hot flashes occurred in 58.6% to 73.0% of men, alongside skeletal or back pain, erectile dysfunction, testicular atrophy, leg swelling and injection-site pain. In the pediatric Triptodur trial, 45% of children had injection-site pain, 13.6% had headache or nasopharyngitis, and 7.7% of girls had transient vaginal bleeding from the initial hormone flare. Labeled warnings also cover bone loss, diabetes, lipid elevations, cardiovascular events, seizures, severe skin reactions and rare pituitary apoplexy.

• How long does triptorelin stay in your system?

  After a 0.5 mg intravenous bolus in healthy men, free triptorelin has a terminal elimination half-life of 2.81 hours (about 3 hours), lengthening to 6.56 to 7.65 hours in renal impairment and 7.58 hours in liver disease. Commercial depot injections release the peptide from polymer microgranules over 4, 12 or 24 weeks, and the pediatric label notes that pituitary-gonadal suppression can persist for 6 to 12 months after treatment stops.

• Is triptorelin legal, and is it banned by WADA?

  As of November 2026, triptorelin is an FDA-approved prescription drug in the US and is not scheduled as a controlled substance under DEA rules (21 CFR 1308.13). In sport, the 2026 WADA Prohibited List bans triptorelin at all times in male athletes under section S2.2.1 (testosterone-stimulating peptides in males).

• Can triptorelin be used alongside GLP-1 medications like semaglutide or tirzepatide?

  No prospective trial has combined triptorelin specifically with a GLP-1 drug, and the FDA labels list no cytochrome P450 interaction. Clinically, androgen deprivation raises blood sugar, fat mass and cardiovascular risk; a 2026 TriNetX cohort study of men with prostate cancer and type 2 diabetes on androgen deprivation therapy found lower all-cause mortality among those prescribed a GLP-1 receptor agonist than among matched users of DPP-4 or SGLT2 inhibitors.

12. Sources