Nafarelin is a synthetic GnRH agonist decapeptide analog (MW ~1322.5 g/mol) with a D-Nal(2) substitution at position 6, administered as a nasal spray (Synarel). It is FDA-approved for the treatment of endometriosis and central precocious puberty. Nafarelin is approximately 200 times more potent than native GnRH and is unique among GnRH agonists in its intranasal route of administration, which avoids injections entirely. Like other GnRH agonists, it achieves sex steroid suppression through the "flare then suppression" mechanism.
Category: Reproductive / Hormonal. Evidence rating: A (strong human clinical data).
Clinical status: FDA-approved (Synarel for endometriosis and central precocious puberty)
Nafarelin is a GnRH agonist with a D-2-naphthylalanine (D-Nal(2)) substitution at position 6, providing approximately 200-fold greater potency than native GnRH and resistance to enzymatic degradation. Following intranasal administration, nafarelin is absorbed through the nasal mucosa with a…
Safety considerations: Nasal irritation: rhinitis, nasal dryness, and epistaxis (approximately 10% of patients); Hot flashes (90% with endometriosis treatment); Decreased bone mineral density (limit treatment to 6 months for endometriosis).
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-08-12.
Related peptides: Kisspeptin, Gonadorelin, Oxytocin.
Compare: Nafarelin vs Kisspeptin, Nafarelin vs Gonadorelin, Nafarelin vs Oxytocin.
Nafarelin is administered as a nasal spray. For endometriosis, one spray (200 mcg) in one nostril in the morning and one spray in the other nostril in the evening. For central precocious puberty, higher doses are used (800 mcg BID, with a possible increase to 800 mcg TID). The nasal spray should be administered while tilting the head back slightly.
Yes, nasal congestion from colds, allergies, or rhinitis may reduce absorption of nafarelin through the nasal mucosa. Patients should avoid nasal decongestant sprays for at least 2 hours after nafarelin administration. If persistent nasal congestion occurs, alternative GnRH agonist routes should be considered.
Treatment for endometriosis is limited to 6 months due to the risk of bone mineral density loss from prolonged hypoestrogenism. Retreatment is generally not recommended unless add-back therapy is used, though this is not part of the FDA-approved labeling for nafarelin.