AbarelixvsGonadorelin (GnRH)

Molecular Formula

C₇₂H₉₅ClN₁₄O₁₄

Molecular Weight

1416.1 g/mol

Half-Life

Approximately 13 days

Bioavailability

~100% (intramuscular depot injection)

CAS Number

183552-38-7

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
• Hot flashes and sweating
• Decreased libido and sexual dysfunction
• Increased liver enzymes
• Injection site reactions (pain, redness, swelling)
• Abdominal pain and gastrointestinal symptoms
• Headache and dizziness
• Weight changes
• Gynecomastia (breast tissue enlargement)
• Bone density loss with long-term use

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 other use

Safety Overview

Abarelix carries significant safety concerns primarily related to histamine release reactions, which led to its voluntary withdrawal from the U.S. market in 2006. Serious allergic responses including anaphylaxis, flushing, and hypotension have been documented. Long-term use poses substantial risks of bone density loss, cardiovascular effects from hormonal suppression, and metabolic complications including weight gain and altered lipid profiles. Liver enzyme elevations occur in 5-10% of patients. All use requires intensive medical supervision with regular monitoring of testosterone levels, liver function, bone density, and cardiovascular markers.

Contraindications

• xPregnancy or lactation
• xSevere hypersensitivity reactions to peptide therapeutics
• xHistory of anaphylaxis with similar compounds

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