Triptorelin (brand name Decapeptyl, Trelstar) is a synthetic GnRH superagonist — a modified decapeptide with ~100x higher receptor binding affinity than endogenous GnRH. Used medically for prostate cancer, endometriosis, and precocious puberty. Also used off-label for HPTA reset after anabolic steroid use.

How does triptorelin work for PCT?

A single ultra-low dose of triptorelin (100 mcg SC) causes an initial LH and FSH surge — the 'flare effect' — that can restart suppressed hypothalamic-pituitary-gonadal axis function after prolonged AAS use. The key is the single-dose approach: repeated dosing would cause suppression instead.

What is the flare effect?

When a GnRH agonist first binds receptors, it causes an initial surge (flare) of LH and FSH lasting 1–3 days. With continued administration, receptors downregulate and gonadotropins fall to castration levels. The PCT use exploits only the flare phase via a single injection.

What dose of triptorelin is used for prostate cancer?

For prostate cancer, triptorelin is given as a depot injection: 3.75 mg IM monthly or 11.25 mg IM every 3 months. This maintains continuous pituitary receptor desensitization, suppressing testosterone to castration levels (<50 ng/dL) for medical androgen deprivation therapy.

GnRH Agonist • Injectable • Rx Only

Triptorelin: The Dual-Action GnRH Superagonist

By Steve B, HighPeptides Editor

Last updated: March 2026

Triptorelin (Decapeptyl) is a GnRH superagonist with ~100× higher receptor affinity than native GnRH. A single ultra-low dose exploits the initial LH/FSH flare for HPTA reset after AAS. Repeated depot doses cause medical castration — used for prostate cancer, endometriosis, and precocious puberty.

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PCT Reset Dose
Single SC Injection

Testosterone Suppression
Oncology Depot Dose

Monthly Depot Dose
Prostate Cancer Rx

📋 On this page

How Triptorelin Works
What the Clinical Trials Show
Side Effects & Risks
Key Takeaways
🛒 Recommended Products
Related Resources

Mechanism of Action

How Triptorelin Works

Triptorelin has a paradoxical dose-dependent biphasic action — it stimulates at first, then profoundly suppresses. Understanding this pharmacology is essential: the same molecule that resets the HPTA at 100 mcg will shut it down at 3.75 mg monthly.

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Phase 1 — The Flare Effect

Upon first binding GnRH receptors, triptorelin causes an immediate burst of LH and FSH — the "flare" — lasting 1–3 days. LH can increase 4–10× above baseline. This flare is the mechanism exploited in PCT use: a single 100 mcg SC injection fires the suppressed pituitary-gonadal axis back to life, potentially jumpstarting recovery after prolonged AAS suppression.

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Phase 2 — Receptor Downregulation

With continued GnRH agonist exposure (as in monthly depot injections), pituitary GnRH receptors are continuously occupied and downregulate. This leads to uncoupling from intracellular signaling, loss of LH/FSH secretion, and subsequent testosterone fall to castration levels (<50 ng/dL) within 2–4 weeks. This phase is the therapeutic mechanism for prostate cancer.

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PCT Application — Single Dose Reset

The theoretical PCT use (100 mcg single SC injection) leverages only Phase 1. The short half-life of the injected peptide means receptor occupancy is brief — enough to fire the flare but not enough to cause sustained downregulation. Published case reports (Buvat et al.) show testosterone recovery within 3 months. However, controlled RCT data is lacking.

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Oncology Mechanism — ADT

For prostate cancer androgen deprivation therapy (ADT), triptorelin 3.75 mg IM monthly or 11.25 mg IM quarterly maintains continuous receptor desensitization. Combined with an anti-androgen for the first 2–4 weeks (to block the initial testosterone flare in oncology patients), it achieves long-term medical castration, reducing prostate cancer growth driven by testosterone.

Research Data

What the Clinical Trials Show

Data from prostate cancer ADT trials and available PCT case literature. Note: high-quality RCT data for PCT use is essentially absent — most evidence is case series and anecdotal.

Initial LH Surge — Flare Effect (first 72 hours)

Peak LH increase above baseline after first GnRH agonist dose

~400–600%

Testosterone Suppression to Castration Level (oncology)

Patients achieving T <50 ng/dL within 4 weeks of depot dosing

~94%

PSA Reduction at 6 Months (prostate cancer)

Serum PSA reduction from baseline during ADT

~85%

HPTA Recovery Rate (PCT — case series)

Testosterone recovery to normal range at 3 months post single-dose triptorelin

~70%

FSH Normalization (PCT case reports)

FSH returning to reference range within 3 months

~65%

Safety Profile

Side Effects & Risks

Hot Flashes (oncology dose)

Most common side effect of long-term ADT with triptorelin

~55%

Injection Site Reaction

Pain, induration at IM injection site — depot formulation

~20%

Erectile Dysfunction (oncology dose)

Consequence of testosterone suppression to castration levels

~30%

Testosterone Flare (initial — oncology)

Paradoxical testosterone spike in first 1–2 weeks — reason anti-androgens are co-prescribed

~100%

Bone Density Loss (long-term oncology)

Osteopenia/osteoporosis risk with prolonged ADT use

~15%

Bottom Line

Key Takeaways

✅ What We Know

Triptorelin causes an initial LH/FSH flare (1–3 days) then suppression with continued use
Single 100 mcg SC injection exploits flare phase for PCT HPTA restart
3.75 mg IM monthly achieves testosterone castration (<50 ng/dL) in ~94% of prostate cancer patients
FDA-approved (Trelstar) for prostate cancer and precocious puberty
PCT use is off-label and based primarily on case series, not RCTs
Anti-androgens must accompany oncology dosing to prevent symptom flare from initial testosterone surge

⚠️ What We Don't Know

No RCTs comparing triptorelin PCT to standard SERM PCT protocols
Optimal timing window for PCT injection post-AAS cessation
Whether triptorelin PCT offers meaningful advantage over clomiphene/enclomiphene PCT
Long-term reproductive outcomes after triptorelin PCT in bodybuilding populations

Supplies

🛒 Recommended Products

Monitoring supplies for post-cycle therapy and hormone tracking.

🧪 Testosterone Test KitMonitor recovery during PCT 📊 LH / FSH Test KitTrack gonadotropin recovery 💉 Insulin SyringesFor SC injection protocols

Keep Reading

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Gonadorelin Guide

Pulsatile GnRH for TRT fertility

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Enclomiphene Guide

Oral SERM PCT and testosterone

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Testosterone & TRT Guide

Complete TRT research overview

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HCG Guide

TRT adjunct for testicular function

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⚠️ Important Disclaimer

This page is for educational purposes only. It is not medical advice. Triptorelin is a prescription drug (Trelstar/Decapeptyl) requiring a licensed healthcare provider. Off-label PCT use is not FDA-approved and lacks controlled trial data. The oncology dosing information is for educational reference only. Never self-administer prescription GnRH agonists. Consult a qualified physician before any hormonal protocol.