FertirelinvsGonadorelin (GnRH)

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

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

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

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

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

• xPregnancy (may disrupt existing pregnancy)
• xHypersensitivity to GnRH analogs
• xActive reproductive infections
• xConcurrent use with certain medications
• xUndiagnosed reproductive disorders

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

• xPregnancy or breastfeeding
• xHormone-sensitive cancers (breast, prostate, ovarian)
• xSevere pituitary or hypothalamic disease
• xUndiagnosed abnormal vaginal bleeding
• xKnown hypersensitivity to GnRH