Peptide profile · Hormone Support

Fertirelin

Name: Fertirelin — Peptide Information
Creator: Michael Carroll

A potent GnRH analog designed to support reproductive function in veterinary and research settings

Written & reviewed by Michael Carroll · Research, Peptide Initiative

Hormone SupportModerate human trialsResearch compound

Typical dose

50-100 mcg per animal

Once dailyCycle: Ongoing/indefiniteOnset: Moderate (1-2 weeks)

Half-life

Variable depending on formulation; sustained-release formulations extend duration

Bioavailability

High when administered via injection

Molecular weight

1153.3 g/mol

Evidence level

Moderate human trials

01 · Compound profile

Scientific & efficacy data

Molecular formula

C₅₅H₇₆N₁₆O₁₂

Primary benefits

Reproductive Synchronization82

Supports reproductive hormone production

Hormone Support78

May support reproductive function in research applications

Veterinary Breeding Enhancement74

Improves timing of breeding and fertility outcomes

Mol. weight1153.3 g/mol

CAS number66002-66-2

PubChem188304

Developed · 1980Research Team
Academic Research Institutions

Amino acid sequence

pGlu-His-Trp-Ser-Tyr-Leu-Leu-Arg-Pro-Gly-NH2

02 · Dosing

How much do I take?

50-100 mcg per animal · single injection at the defined point in the synchronization protocol

Intramuscular: An injection into a muscle, usually the thigh, shoulder, or buttock.

Bioavailability High — well absorbed into the bloodstream from the muscle.

Standard50-100 mcg per animalSingle 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].

Best time to take

Administer Fertirelin at the same time each day (or on the same day each week for weekly injections). Many users prefer morning or evening administration. Pick a time you'll remember consistently.

With food?

Fertirelin injections can be given regardless of meal timing. However, if GI effects occur, administering on an empty stomach or with a light meal may help reduce discomfort.

If stacking

Fertirelin should be used as directed by your healthcare provider. If combining with other medications or supplements, discuss potential interactions with your provider. Avoid combining with compounds that have overlapping mechanisms unless specifically guided by a medical professional.

＋ Increase if

+You've tolerated the current dose for the recommended period without significant side effects
+Therapeutic goals haven't been met at the current dose level
+Your healthcare provider recommends dose escalation based on your response
+Lab work or clinical assessments support a higher dose

－ Decrease if

−Side effects are bothersome or impacting daily life despite management strategies
−You experience any signs of an adverse reaction
−Lab results indicate the need for dose reduction
−Your healthcare provider recommends a lower dose based on your response

✓ Signs of right dose

✓Therapeutic goals being met with minimal side effects
✓Stable and consistent response to treatment
✓Lab values or clinical markers trending in the right direction
✓Good tolerance with manageable or absent side effects

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03 · 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

Alternative approaches for hormone support supportConsult your healthcare provider for alternatives to Fertirelin based on your specific needs and medical history

Alternative hormone-supporting peptidesKisspeptin-10, Gonadorelin, PT-141 (Bremelanotide)

Non-peptide hormone supportClomiphene citrate, Anastrozole, Lifestyle modifications (sleep, exercise)

Do not use if

Pregnancy (may disrupt existing pregnancy)Hypersensitivity to GnRH analogsActive reproductive infectionsConcurrent use with certain medicationsUndiagnosed reproductive disorders

Use with caution if

You are taking other medications—discuss potential interactions with your healthcare providerYou have a history of liver or kidney diseaseYou are elderly or have multiple medical conditionsYou are planning surgery in the near future—inform your surgeon about Fertirelin useYou have any chronic health conditions that require regular monitoring

Not sure?

Compare Fertirelin with similar peptides to find the best fit for your goals.

Fertirelin vs Gonadorelin (GnRH)Fertirelin vs Human Chorionic Gonadotropin (HCG)Fertirelin vs Triptorelin

04 · Administration

How do I use it?

Intramuscular injection · Intravenous injection

Reconstitution — what you need

Fertirelin vial (lyophilized powder or solution)Bacteriostatic water or sterile sodium chloride for reconstitutionAlcohol swabs for cleaning vial tops and injection sitesAppropriately sized syringes with fine-gauge needles (27-30 gauge)Sharps disposal container

Example

Add the recommended volume of bacteriostatic water to the Fertirelin vial. Gently swirl (do not shake) until the powder is fully dissolved. The resulting solution should be clear. Calculate your individual dose based on the concentration and your prescribed amount.

Your dose of Fertirelin is determined by your healthcare provider. Using an insulin syringe marked in units, draw up the exact amount prescribed. For example, if the reconstituted concentration is 1mg/mL and your dose is 0.5mg, draw up 0.5mL (50 units on an insulin syringe). Always double-check calculations before injection.

Full reconstitution guide

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

Abdomen (stomach area)—at least 2 inches from the belly button, most popular choice for self-injectionFront of thighs—middle to upper portion of the outer legBack of upper arm—outer area (may need assistance from another person)

Technique

01Wash your hands thoroughly with soap and water before handling supplies
02Clean the injection site with an alcohol swab and let it air dry completely
03Pinch a fold of skin at the chosen injection site
04Insert the needle at a 45-90 degree angle (depending on needle length and body composition)
05Inject the medication slowly and steadily over 5-10 seconds
06Release the skin fold and remove the needle, applying gentle pressure with a clean swab
07Rotate injection sites to prevent tissue irritation or lipodystrophy
08Dispose of the needle safely in a sharps container—never recap or reuse needles

Fertirelin dosing protocol Fertirelin injection guide

Storage · before reconstitution

Store Fertirelin in the refrigerator at 36-46°F (2-8°C) in its original packaging. Protect from light and moisture. Do not freeze. Check the expiration date before use. Some formulations may be stored at room temperature for limited periods—check your specific product labeling.

Storage · after reconstitution

Once reconstituted, Fertirelin should be kept refrigerated at 36-46°F (2-8°C) and used within the timeframe specified on your product labeling (typically 14-28 days). Label the vial with the reconstitution date. Do not use if the solution appears cloudy, discolored, or contains particles.

Signs of degradation

Solution appears cloudy, discolored, or contains visible particles (should be clear)Product has been exposed to temperatures outside the recommended storage rangeProduct has been frozen (unless specifically designed for freeze-thaw stability)Expiration date has passed or reconstituted solution has exceeded its use-by dateUnusual odor, color change, or visible contamination

Sample daily schedule

As prescribed (once daily)As prescribed by your healthcare provider injection · Site: Intramuscular injection—rotate sites if applicableMaintain a consistent schedule for optimal results with Fertirelin. Set reminders if needed. If you miss a dose, follow your healthcare provider's instructions—do not double up on doses to compensate.

05 · 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 siteSome 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 fluctuationsAs 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 animalsCattle 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 reactionsLocalized 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 appetiteSome 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 variationsAnimals 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 dosesSystemic 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

Occasional swelling at injection site

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

✓Prostaglandin F2 alpha (for breeding synchronization) — May be used together under medical guidance.
✓Progesterone (for reproductive cycling) — May be used together under medical guidance.
✓PMSG (Pregnant Mare Serum Gonadotropin) — May be used together under medical guidance.

With medications

!Dopamine agonists — Use with caution—discuss with your healthcare provider.
!Other GnRH agonists without medical guidance — Use with caution—discuss with your healthcare provider.
!Certain anticonvulsants — Use with caution—discuss with your healthcare provider.

With supplements

✓Multivitamins — Generally safe to take alongside Fertirelin. Space doses apart if taking oral formulations to ensure optimal absorption.
✓Electrolyte supplements — Helpful if experiencing any GI side effects that could lead to dehydration. Safe to combine.

06 · Effectiveness

How do I know it's working?

Moderate human trials · first signs 0-6 hours

Evidence level

Moderate human trials

(Phase 1-2)

80/100

How it works

Fertirelin is a natural GnRH hormone used to stimulate fertility in animals and humans. Unlike GnRH agonists that eventually suppress hormones, fertirelin provides direct GnRH stimulation to trigger hormone release.

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

•GnRH receptors activated, hormone cascade begins
•Fertirelin binds to pituitary GnRH receptors, triggering follicle-stimulating hormone (FSH) and luteinizing hormone (LH) release

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

Signs it's working · 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

[1]“Effect of fertirelin acetate or buserelin on conception rate at first or second insemination in lactating dairy cows”Chenault JR, 1990Finding: Fertirelin acetate improved conception rates in lactating dairy cows when administered for timed insemination. The GnRH agonist effectively synchronized ovulation and improved fertility outcomes in breeding programs.View study

[2]“Effects of LHRH-analogue treatment of spermatogenic dysfunction in the dog”Kawakami E, Tonsho H, Tsutsui T, 1991Finding: LHRH analogs improved sperm quality in dogs by temporarily raising testosterone and LH levels. Treatment restored fertility within 30 days, with sperm abnormalities decreasing from 19-32% to 10-16%.View study

[3]“Induction of fertile estrus in bitches using a sustained-release formulation of a GnRH agonist (leuprolide acetate)”Inaba T, Tani H, Gonda M, 1998Finding: GnRH agonist depot formulations successfully induced fertile estrus in female dogs, allowing precise control of breeding timing. Long-acting formulations provided sustained hormone effects for reproductive management.View study

[4]“Influence of GnRH analogue (fertirelin acetate) doses on synchronization of ovulation and fixed-time artificial insemination in lactating dairy cows”Yamada K, et al., 2002Finding: In lactating dairy cows, intramuscular fertirelin acetate at 50 mcg and 100 mcg both raised plasma LH above 5 ng/mL ~120 min post-injection with comparable conception rates (61.1% vs 59.5%), supporting 50-100 mcg IM for ovulation synchronization.View study

07 · 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.

08 · 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 Fertirelin

Fertirelin

A potent GnRH analog designed to support reproductive function in veterinary and research settings

Written & reviewed by Michael Carroll · Research, Peptide Initiative

Hormone SupportModerate human trialsResearch compound

Typical dose

50-100 mcg per animal

Once dailyCycle: Ongoing/indefiniteOnset: Moderate (1-2 weeks)

Peptide Database

Scientific & efficacy data

How much do I take?

Step 1: Peptide Weight

Is this right for me?

How do I use it?

Is it safe?

How do I know it's working?

Frequently asked

History & related research

Scientific & efficacy data

How much do I take?

Step 1: Peptide Weight

Is this right for me?

How do I use it?

Is it safe?

How do I know it's working?

Frequently asked

History & related research