Fertirelin
A potent GnRH analog designed to support reproductive function in veterinary and research settings
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Suggested dose
50 – 100 mcg
Compound profile
Scientific & efficacy data
Hormone Support
Peptide profile
Moderate human trials
Fertirelin
50-100 mcg per animal · Once daily
Molecular formula
C55H76N16O12
- Mol. weight
- 1153.3 g/mol
- CAS number
- 66002-66-2
- PubChem
- 188304
- Developed · 1980
- Research Team
Academic Research Institutions
Amino acid sequence
pGlu-His-Trp-Ser-Tyr-Leu-Leu-Arg-Pro-Gly-NH2Reproductive Synchronization
Supports reproductive hormone production
Hormone Support
May support reproductive function in research applications
Veterinary Breeding Enhancement
Improves timing of breeding and fertility outcomes
Dosing
How much do I take?
50 – 100 mcg · single injection at the defined point in the synchronization protocol
50 – 100 mcg
Single injection at the defined point in the synchronization protocol
Covers timing · dose-adjustment guidance.
Suitability
Is this right for me?
Best for livestock breeding programs & reproductive synchronization in cattle
Best 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.
Consider alternatives if
Do not use if
Use with caution if
Not sure?
Compare Fertirelin with similar peptides to find the best fit for your goals.
Administration
How do I use it?
Intramuscular injection · Intravenous injection
Route
Subcutaneous injection (into the fatty tissue just under the skin)—allows for consistent absorption and can be self-administered at home after proper training
Best sites
Covers reconstitution · step-by-step technique · storage · a sample daily schedule.
Safety
Is it safe?
7 common side effects · 1 serious
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.
Fertirelin's safety and efficacy data comes primarily from veterinary medicine, where it has been approved for cattle reproduction since 1981 in Japan. The peptide is 15-20 times more potent than natural GnRH at stimulating LH release.
Human clinical data is extremely limited, with no FDA or EMA approval for any human indication.
Common side effects · experienced by some users
Mild discomfort at treatment site
Some users experience mild discomfort, which is among the most commonly reported effects with Fertirelin. This typically resolves within a few days as the body adjusts.
Management: Apply ice if needed. Rotate treatment sites. These symptoms typically improve within the first week of use.
Transient hormone fluctuations
As a GnRH agonist, Fertirelin triggers an initial surge in FSH and LH (flare effect) within the first few days, followed by suppression. This biphasic response occurs in 60-80% of users and is expected. Animals may show increased reproductive behavior for 2-4 days before suppression begins.
Management: This is an expected physiologic response. Monitor for signs of exaggerated reproductive behavior. If using in breeding protocols, time applications accordingly. Discuss timing strategy with your veterinarian to optimize breeding outcomes.
Temporary behavioral changes in animals
Cattle and other livestock frequently show increased mounting behavior, vocalizations, and restlessness during the first 24-72 hours after injection, related to the initial hormone surge. These behavioral changes typically resolve as the flare effect subsides and suppression begins.
Management: Keep animals in secure enclosures during the first 48-72 hours post-injection. Provide adequate space and minimize handling stress. Separate animals if aggressive mounting occurs. These behaviors are temporary and expected, not a sign of adverse reactions.
Mild injection site reactions
Localized inflammation at the injection site occurs in approximately 15-20% of animals. This typically includes mild redness and slight induration that develops within hours and resolves within 3-7 days. Is rarely associated with infection or serious complications.
Management: Rotate injection sites between treatments to different areas of the neck or hindquarters. Use sterile injection technique. Apply ice packs if swelling is moderate. Monitor for signs of infection (increasing warmth, pus, fever). Most reactions resolve without intervention.
Short-term changes in appetite
Some animals experience decreased feed intake for 1-2 days immediately after Fertirelin injection, correlating with the behavioral changes from the initial hormone surge. Feed consumption typically normalizes by day 3-4 as hormone levels stabilize.
Management: Ensure animals have access to water and hay during the first few days. Continue offering feed even if intake is reduced; appetite usually returns spontaneously. Contact your veterinarian if appetite remains reduced beyond 4 days or if the animal appears distressed.
Temporary mood variations
Animals may appear more irritable or aggressive during the 24-72 hour period following injection due to elevated hormones. Restlessness and hyperreactivity are common. These mood changes correlate with the flare effect and typically resolve as LH suppression begins.
Management: Minimize stressful handling and procedures during the first 72 hours post-injection. Provide a calm environment. Avoid mixing treated and untreated animals if aggression is significant. These behavioral changes are temporary and expected with GnRH agonists.
Minimal systemic effects at therapeutic doses
Systemic side effects are uncommon at recommended veterinary doses (25-100 mcg). Most therapeutic responses are localized to reproductive and behavioral systems. Animals rarely show signs of systemic toxicity or off-target organ effects when using proper injection technique and staying within established dosing guidelines.
Management: Maintain strict adherence to veterinary dosing recommendations. Monitor general health status (appetite, activity, temperature) during the first week. Report any unexpected systemic signs (severe lethargy, vomiting, fever) to your veterinarian immediately, though these are rare.
Less common
These typically resolve with continued use or dose adjustment.
Stop and seek help if
- Severe or worsening side effects that don't improve with dose adjustment or supportive care
- Signs of an allergic reaction—rash, hives, swelling, or difficulty breathing
- Your healthcare provider recommends discontinuation based on your clinical response
- Development of any new medical condition that may be contraindicated with Fertirelin
- Pregnancy or planning to become pregnant (unless specifically approved for use during pregnancy)
- Abnormal lab results or clinical markers that suggest adverse effects
Fertirelin should only be started, adjusted, or discontinued under medical supervision. This information is for educational purposes only and does not replace professional medical advice. Never stop a prescribed treatment without consulting your healthcare provider first, as abrupt discontinuation may have consequences.
With other peptides
- Safe:Prostaglandin F2 alpha (for breeding synchronization) — May be used together under medical guidance.
- Safe:Progesterone (for reproductive cycling) — May be used together under medical guidance.
- Safe:PMSG (Pregnant Mare Serum Gonadotropin) — May be used together under medical guidance.
With medications
- Caution:Dopamine agonists — Use with caution—discuss with your healthcare provider.
- Caution:Other GnRH agonists without medical guidance — Use with caution—discuss with your healthcare provider.
- Caution:Certain anticonvulsants — Use with caution—discuss with your healthcare provider.
With supplements
- Safe:Multivitamins — Generally safe to take alongside Fertirelin. Space doses apart if taking oral formulations to ensure optimal absorption.
- Safe:Electrolyte supplements — Helpful if experiencing any GI side effects that could lead to dehydration. Safe to combine.
Effectiveness
How do I know it's working?
Moderate human trials · first signs 0-6 hours
Evidence level
Moderate human trials
(Phase 1-2)
Regulatory status
Research compound
Onset of effects
Moderate
(1-2 weeks)
How it works
The deeper mechanism
Fertirelin is native GnRH (gonadotropin-releasing hormone) that directly activates GnRH receptors on pituitary gonadotrophs, stimulating FSH and LH release.
What to expect
0-6 hours
What you might notice
What's normal
- Initial response to Fertirelin is beginning at the cellular level
- Different individuals experience Fertirelin's onset at different rates
- Transient systemic effects from initial Fertirelin exposure are common
What's next
- Maintain consistent Fertirelin administration as prescribed
- Document subjective effects and physical markers daily
- Schedule a check-in with your provider about initial observations
6-24 hours
What you might notice
- Ovarian response develops
- Follicle growth accelerates and hormonal support increases, setting the stage for ovulation
What's normal
- Fertirelin is achieving sufficient receptor engagement
- Initial mechanism of Fertirelin is taking effect
- Early transient effects from Fertirelin administration are resolving
What's next
- Maintain consistent Fertirelin administration as prescribed
- Document subjective effects and physical markers daily
- Schedule a check-in with your provider about initial observations
24-72 hours
What you might notice
- Ovulation occurs
- Peak hormone surge triggers the release of the egg, allowing for proper timing of insemination
What's normal
- Fertirelin response patterns are emerging
- Initial Fertirelin response is consistent with mechanism expectations
- Early tolerance development to Fertirelin is not expected
What's next
- Assess whether Fertirelin response aligns with expectations
- Plan next steps based on initial Fertirelin tolerance and response
- Establish baseline monitoring for Fertirelin response tracking
Signs it's working
Treatment Response
- Improvement in the primary symptoms or condition being treated
- Positive changes in relevant lab values or clinical markers
- Consistent, stable response to Fertirelin over time
- Reduction in symptom frequency or severity
General Well-being
- Improved energy levels and daily functioning
- Better quality of life related to the treated condition
- Manageable or absent side effects indicating good tolerance
- Positive feedback from healthcare provider during check-ups
Not seeing results? Common reasons
- Not at therapeutic dose yet—initial doses are for building tolerance, not maximum effect
- Insufficient time at target dose—most compounds need several weeks to show full benefits
- Inconsistent dosing schedule—regular, consistent use is crucial for optimal results
- Individual variation in response—genetics, metabolism, and other factors affect outcomes
- Underlying conditions or medications interfering with absorption or effectiveness
- Improper storage leading to degraded product—always verify proper storage conditions
Key research
Questions
Frequently asked
What exactly is Fertirelin?
Fertirelin is a man-made version of a natural hormone called GnRH (gonadotropin-releasing hormone). It tells the body's pituitary gland to release hormones that control reproduction. It's used mainly in animals like cattle to help with breeding.
When was Fertirelin first developed?
Fertirelin was first approved and introduced in Japan in 1981 under the brand name Ovalyse. It was designed to help cattle with ovarian problems and became widely used in veterinary breeding programs around the world.
How much more powerful is Fertirelin than natural GnRH?
Fertirelin is about 15 to 20 times more biologically active than the natural GnRH hormone. This means a much smaller dose can create a stronger effect, making it very efficient for veterinary use.
Is Fertirelin safe for animals?
Yes, Fertirelin has been safely used in veterinary medicine for over 40 years. It's well-tolerated by animals when used according to veterinary guidelines. Side effects are usually mild and temporary, like brief behavior changes or injection site reactions.
Can Fertirelin be used in humans?
Fertirelin is approved only for veterinary use, especially in cattle and other livestock. While it's a research compound, it should not be used in humans without proper medical supervision and authorization. Other GnRH analogs like leuprorelin (Lupron) are specifically approved for human medical use.
Further reading
History & related research
History · since 1981
The peptide that helped feed billions by making cattle fertile
A hormone peptide that controls reproduction in livestock. It signals the body to synchronize ovulation in cattle.
Read the full history of FertirelinReady for the protocol?
Every dosing tier, administration route, timing note, and dose-adjustment rule for Fertirelin, on one page.