Fertirelin vs Gonadorelin (GnRH)
A potent GnRH analog designed to support reproductive function in veterinary and research settings
The master hormone that controls your reproductive system and fertility
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
Fertirelin
50–100 mcg
Gonadorelin (GnRH)
100–100 mcg
Frequency
Fertirelin
Once daily
Gonadorelin (GnRH)
Once daily
Administration
Fertirelin
Intramuscular injection
Gonadorelin (GnRH)
Subcutaneous injection
Cycle length
Fertirelin
Ongoing/indefinite
Gonadorelin (GnRH)
Ongoing/indefinite
Onset speed
Fertirelin
Moderate (1-2 weeks)
Gonadorelin (GnRH)
Moderate (1-2 weeks)
Evidence level
Fertirelin
Moderate human trials (Phase 1-2)
Gonadorelin (GnRH)
Moderate human trials (Phase 1-2)
Benefit ratings
Reproductive Synchronization
Hormone Support
Veterinary Breeding Enhancement
Reproductive Health
Hormone Balance
Ovulation Support
Compound specifications
Fertirelin
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
Gonadorelin (GnRH)
Molecular formula
C55H75N17O13
Molecular weight
1182.3
Half-life
2-4 minutes
Bioavailability
Varies by route: ~5-20% (intranasal), 100% (IV/IM injections)
CAS number
34973-08-5
Dosing compared
Fertirelin
Intramuscular
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].
Gonadorelin (GnRH)
Subcutaneous
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].
Intravenous
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.
Best suited for
Fertirelin
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.
Gonadorelin (GnRH)
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.
Side effects
Fertirelin
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
Gonadorelin (GnRH)
Common
- 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
Serious
- Severe allergic reaction
Safety & evidence
Fertirelin
Evidence level
Moderate human trials (Phase 1-2)
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
- Pregnancy (may disrupt existing pregnancy)
- Hypersensitivity to GnRH analogs
- Active reproductive infections
- Concurrent use with certain medications
- Undiagnosed reproductive disorders
Gonadorelin (GnRH)
Evidence level
Moderate human trials (Phase 1-2)
FDA status
FDA approved for this use
Safety overview
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.
Contraindications
- Pregnancy or breastfeeding
- Hormone-sensitive cancers (breast, prostate, ovarian)
- Severe pituitary or hypothalamic disease
- Undiagnosed abnormal vaginal bleeding
- Known hypersensitivity to GnRH
Which is right 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