Educational guide
Fertirelin vs Gonadorelin (GnRH) — Peptide Comparison
At a Glance Quickcomparison Dose Range Fertirelin 25 micrograms–100 micrograms mg Gonadorelin (GnRH) 0.1-1.5–3-10 mg Frequency Once daily Administration Intramuscular injection Subcutaneous injection Cycle Length Ongoing/indefinite Onset Speed Moderate (1-2 we
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At a Glance
Quickcomparison
Dose Range
Fertirelin
25 micrograms–100 micrograms mg
Gonadorelin (GnRH)
0.1-1.5–3-10 mg
Frequency
Once daily
Administration
Intramuscular injection
Subcutaneous injection
Cycle Length
Ongoing/indefinite
Onset Speed
Moderate (1-2 weeks)
Evidence Level
Moderate human trials (Phase 1-2)
Efficacy
Benefitratings
Reproductive Synchronization
Hormone Support
Veterinary Breeding Enhancement
Reproductive Health
Hormone Balance
Ovulation Support
Technical Data
Compoundspecifications
Molecular Formula
C55H76N16O12
Molecular Weight
1153.3 g/mol
Half-Life
Variable depending on formulation; sustained-release formulations extend duration
Bioavailability
High when administered via injection
CAS Number
66002-66-2
C55H75N17O13
1182.3
2-4 minutes
Varies by route: ~5-20% (intranasal), 100% (IV/IM injections)
34973-08-5
Protocols
Dosingtiers
standard
50-100 mcg per animal
Single injection at the defined point in the synchronization protocol
Single dose (repeated per breeding cycle as needed)
Fertirelin is a veterinary GnRH agonist. In dairy cattle, 50 mcg and 100 mcg intramuscular both triggered an LH surge and comparable conception rates for ovulation synchronization and fixed-time insemination [4]. Used to induce ovulation and improve conception in cattle [1].
100 mcg
Single dose
One-time diagnostic test
FDA-labeled gonadotropin (LH/FSH) stimulation test for pituitary reserve; 100 mcg given once subcutaneously (or IV), with LH measured at 0, 15, 30, 45, 60 and 120 minutes (Factrel) [4].
5 mcg per pulse (range 1-20 mcg)
Every 90 minutes via pulsatile pump
One or more ovulatory cycles; reassessed at 21-day intervals
FDA-labeled pulsatile regimen for ovulation induction in hypothalamic amenorrhea (Lutrepulse); intravenous pulsatile delivery gave better results than subcutaneous [5]. The 2-4 minute half-life makes pulsatile delivery essential.
Applications
Bestsuited for
Livestock breeding programs
Fertirelin is particularly well-suited for individuals focused on livestock breeding programs. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Reproductive synchronization in cattle
Fertirelin is particularly well-suited for individuals focused on reproductive synchronization in cattle. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Fertility enhancement in veterinary settings
Fertirelin is particularly well-suited for individuals focused on fertility enhancement in veterinary settings. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Research on reproductive hormone mechanisms
Fertirelin is particularly well-suited for individuals focused on research on reproductive hormone mechanisms. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Improving fertility and conception chances
Gonadorelin (GnRH) is particularly well-suited for individuals focused on improving fertility and conception chances. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Regulating irregular menstrual cycles
Gonadorelin (GnRH) is particularly well-suited for individuals focused on regulating irregular menstrual cycles. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Enhancing reproductive hormone levels
Gonadorelin (GnRH) is particularly well-suited for individuals focused on enhancing reproductive hormone levels. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Supporting natural pregnancy attempts
Gonadorelin (GnRH) is particularly well-suited for individuals focused on supporting natural pregnancy attempts. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Safety Profile
Sideeffects
Common
Mild discomfort at treatment site
Transient hormone fluctuations
Temporary behavioral changes in animals
Mild injection site reactions
Short-term changes in appetite
Temporary mood variations
Minimal systemic effects at therapeutic doses
Uncommon
Occasional swelling at injection site
Serious
Severe allergic reaction
Mild headache
Local injection site reactions (redness, swelling)
Temporary hot flashes
Mood changes or emotional sensitivity
Nausea or mild stomach upset
Allergic skin reactions
Dizziness or lightheadedness
Temporary changes in vision
Joint or muscle aches
Insomnia or sleep disturbances
Severe allergic reactions (difficulty breathing, swelling)
Severe hormonal imbalance symptoms
Ovarian hyperstimulation syndrome (OHSS)
Signs of blood clots (chest pain, leg swelling)
Severe mood changes or depression
Research Status
Safety& evidence
FDA Status
Research compound
Safety Overview
Fertirelin is a GnRH agonist developed specifically for veterinary use in livestock, particularly cattle breeding and fertility management. The peptide has been safely used in veterinary medicine for over 40 years with a well-documented safety profile in animals. Important limitation: Fertirelin is NOT approved for human use. All safety and efficacy data comes from veterinary applications in cattle and limited laboratory research. Human safety data is minimal and extrapolation from veterinary use is problematic. The biphasic response (initial hormone surge followed by suppression) must be carefully managed in any application. Individual responses can vary significantly based on age, hormonal status, and concurrent medications.
Contraindications
xPregnancy (may disrupt existing pregnancy)
xHypersensitivity to GnRH analogs
xActive reproductive infections
xConcurrent use with certain medications
xUndiagnosed reproductive disorders
FDA approved for this use
Gonadorelin is native GnRH and carries the safety profile established over 40+ years of clinical use in reproductive endocrinology. As the body's natural hormone, it produces minimal local side effects when dosed appropriately. The critical safety concern with gonadorelin is the initial flare effect within 24-48 hours of first dose—temporary elevation in FSH and LH—which can paradoxically suppress sex hormones before the desired stimulation occurs. This flare makes gonadorelin unsuitable for some conditions and explains why synthetic analogs (agonists, antagonists) are preferred in many modern fertility protocols.
xPregnancy or breastfeeding
xHormone-sensitive cancers (breast, prostate, ovarian)
xSevere pituitary or hypothalamic disease
xUndiagnosed abnormal vaginal bleeding
xKnown hypersensitivity to GnRH
Decision Guide
Which isright for you?
Choose Fertirelin if...
Livestock breeding programs
Reproductive synchronization in cattle
Fertility enhancement in veterinary settings
Research on reproductive hormone mechanisms
Choose Gonadorelin (GnRH) if...
Improving fertility and conception chances
Regulating irregular menstrual cycles
Enhancing reproductive hormone levels
Supporting natural pregnancy attempts