Gonadorelin (GnRH)vsLeuprolide

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

Molecular Formula

C₅₉H₈₄N₁₆O₁₂

Molecular Weight

1209.4 g/mol

Half-Life

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

Bioavailability

~95% (subcutaneous injection)

CAS Number

74381-53-6

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

Common

• Hot flashes (very common in men)
• Decreased libido and erectile dysfunction
• Injection site pain or swelling
• Nausea
• Fatigue
• Mood changes or depression
• Joint or muscle pain
• Headaches
• Dizziness
• Thinning hair
• Decreased bone density (osteoporosis with long-term use)
• QT prolongation (rare but serious cardiac effect)
• Tumor flare (temporary worsening of cancer symptoms in first weeks)
• Severe allergic reactions
• Spinal cord compression risk in men with metastatic disease

Serious

• Severe allergic reaction

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

Evidence Level

Strong human trials (Phase 3 or FDA approved)

FDA Status

FDA approved for this use

Safety Overview

Leuprolide (Lupron) is an FDA-approved GnRH agonist with 35+ years of clinical safety data involving millions of patients in oncology and endocrinology. The critical safety issue is the initial 5-7 day flare effect—temporary surge in FSH/LH causing symptom worsening before hormone suppression begins—particularly dangerous for prostate cancer patients (flare can cause urinary obstruction or spinal cord compression). Bone density loss is a dose-dependent long-term risk in both men and women requiring monitoring. Injection site reactions, hot flushes, and initial hypogonadal symptoms are expected and typically transient.

Contraindications

• xPregnancy or breastfeeding (teratogenic)
• xUndiagnosed vaginal bleeding
• xActive bone metastases with spinal cord compression (increased fracture risk)
• xAllergy to GnRH agonists or components
• xSevere cardiovascular disease with QT prolongation risk