CetrorelixvsGonadorelin (GnRH)

Molecular Formula

C₇₀H₉₂ClN₁₇O₁₄

Molecular Weight

1431.06 Da

Half-Life

Approximately 2-6 hours (varies by route of administration)

Bioavailability

~85% (subcutaneous injection)

CAS Number

100885-89-0

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

• Injection site reactions (redness, itching, swelling)
• Headache
• Nausea
• Mild abdominal discomfort
• Dizziness
• Allergic reactions (rash, difficulty breathing)
• Ovarian hyperstimulation syndrome (OHSS) if used with other fertility drugs
• Ovarian cysts
• Vaginal bleeding
• Mood changes
• Liver enzyme changes
• Pelvic pain
• Severe allergic reaction

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

Strong human trials (Phase 3 or FDA approved)

FDA Status

FDA approved for this use

Safety Overview

Cetrorelix is an FDA-approved GnRH antagonist used exclusively in assisted reproductive technology with proven safety in short-term reproductive cycles. Unlike GnRH agonists, cetrorelix lacks the initial testosterone flare, making it well-tolerated for ovarian stimulation. Primary side effects are mild and local—injection site reactions (erythema, bruising) occur in 10-20% of patients. No systemic bone loss, cardiovascular complications, or serious adverse events have been reported in the reproductive context where treatment duration is limited (typically 7-10 days). The short treatment window in IVF protocols minimizes long-term safety concerns. Hypersensitivity reactions are rare but possible.

Contraindications

• xKnown allergy to cetrorelix or any ingredient
• xPregnancy (it may harm the developing baby)
• xUndiagnosed vaginal bleeding
• xSevere liver or kidney disease
• xLatex allergy (some syringes contain latex)

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