Nafarelin

A synthetic decapeptide GnRH agonist delivered as a metered nasal spray, FDA approved since 1990 for endometriosis and later for central precocious puberty, that suppresses gonadotropin and sex-steroid output through pituitary desensitization.

Also referenced as: Nafarelin acetate, Synarel, Synarela, RS-94991, RS 94991, D-Nal(2)6-GnRH, D-Nal(2)6-LHRH, Nafareline

Also appears in: Other

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What is Nafarelin?

Nafarelin is a synthetic decapeptide analog of gonadotropin-releasing hormone (GnRH) in which the glycine at position 6 of the native sequence is replaced by 3-(2-naphthyl)-D-alanine, a bulky hydrophobic substitution that makes the molecule markedly more potent and longer-acting than GnRH itself. Developed by Syntex under the code RS-94991, it was approved by the FDA on February 13, 1990 as Synarel, a metered nasal spray, for the management of endometriosis; the same product is also indicated for central precocious puberty (CPP) in children. It remains the only intranasal GnRH agonist approved in the United States, which is the main reason it is discussed separately from the injectable and implantable agonists leuprolide, triptorelin, goserelin, and histrelin.

It appears in research-peptide conversations because of its place in the GnRH agonist class, which is widely used experimentally to switch the hypothalamic-pituitary-gonadal axis off and on, and because its needle-free route has drawn renewed interest in reproductive medicine, including as an ovulation trigger.

How it works

Nafarelin acts at the GnRH receptor on pituitary gonadotroph cells. Like other agonists in the class, it produces a biphasic response: an initial surge in gonadotropin release followed by profound suppression when the receptor is continuously occupied.

• Initial stimulation, then desensitization — early doses raise LH and FSH, but with repeated administration the gonadotrophs become refractory. In 32 ovulatory women given 125, 250, or 1,000 mcg of intranasal nafarelin daily for 6 months, suppression of LH was dose-dependent, peak LH responses to each dose fell by about 70% at the two lower doses and about 95% at the highest, and ovulation was reliably blocked at 250 mcg and above (Monroe et al., Journal of Clinical Endocrinology & Metabolism, 1986, 63(6):1334–1341)
• Reversible hypogonadal state — the resulting loss of pulsatile gonadotropin drive lowers ovarian estradiol or testicular testosterone to postmenopausal or prepubertal ranges within roughly 1 to 4 weeks, which is the therapeutic lever in both endometriosis (estrogen-dependent lesions regress) and CPP (sex-steroid-driven maturation halts). In the same dose-ranging study, ovulatory menstrual function returned rapidly in all women once dosing stopped (Monroe et al., Journal of Clinical Endocrinology & Metabolism, 1986)
• Rapid nasal absorption and peptidase clearance — in the original human pharmacokinetic work, nafarelin reached peak serum levels 20 to 40 minutes after intranasal dosing but was not absorbed after sublingual or vaginal administration; its serum half-life was about 2 hours, and after a radiolabeled subcutaneous dose it was broken down into short peptide fragments plus naphthylalanine and 2-naphthylacetic acid (Chan et al., Clinical Pharmacology & Therapeutics, 1988, 44(3):275–282). The approved spray’s label reports peak levels at 10 to 40 minutes, a half-life of about 3 hours in adults (2.5 hours in children), and mean absolute bioavailability of 2.8% from a 400 mcg nasal dose; it notes that nafarelin is degraded by peptidases rather than cytochrome P450 enzymes (Synarel label)
• Class-wide bone effect of estrogen withdrawal — the induced hypoestrogenism increases bone resorption. In a randomized, double-blind trial of 94 women given nafarelin 400 mcg daily for 6 months, spinal bone density fell by 3.9% to 6.1% across arms regardless of whether placebo or up to 2.45 mg of norethisterone was added, and had returned to baseline 6 months after treatment stopped (Eldred et al., Clinical Endocrinology, 1992, 37(4):354–359)

Research status

Nafarelin’s human evidence base was built in the 1980s and 1990s and is mature for its two approved uses; it has not been extended to new indications in the United States.

Endometriosis (pivotal trial). The registration study randomized 213 women with laparoscopically confirmed endometriosis to 6 months of nasal nafarelin at 400 or 800 mcg per day or oral danazol 800 mg per day, with double-dummy placebo. More than 80% of patients in every group had a reduction in laparoscopic disease extent; mean American Fertility Society scores fell from 20.4 to 11.7 (nafarelin 400 mcg), 21.9 to 12.6 (nafarelin 800 mcg), and 18.4 to 10.5 (danazol), with no significant between-group differences. The share of women with severe pain dropped from about 40% to 5–10%. Danazol lowered HDL and raised LDL cholesterol; nafarelin did not, but produced more hot flashes and reduced libido (Henzl et al., New England Journal of Medicine, 1988, 318(8):485–489). An earlier open-label study from the same group had established the effect in eight women (Schriock et al., Fertility and Sterility, 1985, 44(5):583–588). The current label also cites a single controlled trial in which 400 mcg per day was clinically comparable to monthly intramuscular leuprolide depot 3.75 mg, and reports a mean 8.7% loss of vertebral trabecular bone density by quantitative CT after 6 months with partial recovery afterward.

Add-back and lower-dose work. A two-center double-blind trial of 49 women compared nafarelin 200 mcg, 400 mcg, and 200 mcg plus norethisterone 1.2 mg daily; the lower dose relieved symptoms as well as the standard dose, and the progestin arm had fewer hot flushes in the first month and better bleeding control (Bergqvist et al., Gynecological Endocrinology, 1997, 11(3):187–194). A Swedish report of two 6-month studies found that bone mineral measurements remained stable at 200 mcg per day but fell significantly at 400 mcg, recovering within 6 months of stopping (Jacobson, American Journal of Obstetrics and Gynecology, 1990, 162(2):591–592). The larger Newcastle trial described above found that norethisterone did not eliminate the spinal bone loss at 400 mcg (Eldred et al., Clinical Endocrinology, 1992). Add-back regimens are not part of the U.S. nafarelin label.

Central precocious puberty. An early pediatric series treated 15 girls with gonadotropin-dependent precocious puberty with 800 to 1,200 mcg of intranasal nafarelin per day for 6 months and documented suppression of estradiol, urinary gonadotropins, vaginal cytology, and growth velocity (Lin et al., Journal of Pediatrics, 1986, 109(6):954–958). A prospective Chicago study of 21 girls with idiopathic precocious puberty treated the 14 with impaired height prognosis with nafarelin; after 2 years, predicted adult height improved modestly, from 150.7 to 152.7 cm (Kreiter et al., Journal of Pediatrics, 1990, 117(3):364–370). The approved label reports that, in the labeled pediatric program, the LH response to GnRH stimulation fell to prepubertal levels within one month, breast development arrested or regressed in 82% of girls and genital development in 100% of boys, growth velocity fell to about 5–6 cm per year or less in most children in the first year, and suppression reversed in all 69 children with one year of post-treatment follow-up. The 2009 Lawson Wilkins/ESPE consensus statement on GnRH analogs in children, which covers the class rather than nafarelin specifically, concluded that the adult-height benefit is undisputed only in early-onset CPP (girls under 6) and that few controlled prospective studies exist (Carel et al., Pediatrics, 2009, 123(4):e752–e762).

Off-label and investigational uses. Nafarelin has been used for pituitary down-regulation in IVF, where a small double-blind comparison found no differences from leuprolide (Corson et al., International Journal of Fertility and Menopausal Studies, 1996, 41(5):446–449) and a randomized single-blind trial of 240 women compared it with buserelin in long-protocol cycles (Lockwood et al., Human Reproduction, 1995, 10(2):293–298). Earlier studies examined it for uterine leiomyomas with MRI follow-up (Andreyko et al., American Journal of Obstetrics and Gynecology, 1988, 158(4):903–910) and for hirsutism (Andreyko et al., Journal of Clinical Endocrinology & Metabolism, 1986, 63(4):854–859); neither led to an approved indication. Nafarelin has also been used as a single-dose stimulation test to probe ovarian steroidogenesis in polycystic ovary syndrome (Barnes et al., New England Journal of Medicine, 1989, 320(9):559–565). The one actively recruiting trial in which nafarelin is itself the investigational product is a Phase 4, open-label non-inferiority study at Fundación Dexeus, Barcelona, comparing a single 800 mcg intranasal nafarelin dose with 200 mcg subcutaneous triptorelin for triggering final oocyte maturation in fertility-preservation cycles (NCT06763926; started October 2026, estimated enrollment 154, estimated completion January 2028). Other registered studies list nafarelin only as a component of IVF protocols.

Regulatory record. NDA 019886 was approved on February 13, 1990 as a new molecular entity; the CPP indication was added to the label subsequently. The most recent U.S. labeling actions are a package-insert supplement approved January 31, 2023 and a Medication Guide supplement approved November 24, 2025; the current DailyMed label, posted in March 2026, carries a November 2025 revision date. No new indication, formulation, or generic has been approved in 2025 or 2026. The brand has had intermittent supply constraints outside the United States, including a Canadian manufacturing disruption that ran from late October 2023 to January 2024 and a French supply tension logged in March 2026, with the manufacturer’s May and June 2026 letters to prescribers announcing rationed distribution reserved for patients already on treatment.

Common dosage forms

• Metered nasal spray (approved product) — a solution of 2 mg/mL nafarelin (expressed as base) in an 8 mL bottle with a metered pump, each actuation delivering about 100 µL containing about 200 mcg of nafarelin; the bottle is labeled for 60 metered sprays. The formulation contains benzalkonium chloride as a preservative, with sorbitol, glacial acetic acid, pH adjusters, and purified water as excipients. The same product is marketed abroad as Synarel and, in several Nordic countries and Germany, as Synarela.
• No injectable, depot, or implant form — unlike every other GnRH agonist approved in the United States, nafarelin has no marketed parenteral or sustained-release presentation. Subcutaneous dosing appears only in early pharmacokinetic studies.
• Research supply — nafarelin acetate as lyophilized powder or as an analytical reference standard, labeled by mass. These are not nasal formulations and have no bioavailability data behind them in any route.

Key considerations

• Approved, but for two narrow indications and with a time limit. Nafarelin’s FDA Approved status reflects an approved drug product (Synarel) for endometriosis in women 18 and older and for central precocious puberty in children. The endometriosis indication is supported by a single 6-month course; the label states that retreatment cannot be recommended because safety data beyond 6 months are not available, and that some of the bone-density loss during treatment may not be reversible. Nothing in the record supports use for fertility enhancement, body composition, hormone “optimization,” or any wellness framing.
• The dominant safety signal is bone loss from estrogen withdrawal. Label and trial data consistently show vertebral bone density falling by roughly 4% to 9% over a 6-month course, with recovery that is partial to complete after stopping. Progestin add-back reduced vasomotor symptoms in trials but did not reliably prevent the bone effect at the standard dose, and add-back is not labeled for nafarelin in the United States. Other labeled warnings and precautions include ovarian cysts in the first two months of therapy, clinical depression and other psychiatric events, severe cutaneous adverse reactions, and post-marketing reports of convulsions, pituitary apoplexy, and venous and arterial thromboembolic events; the label states that the drug does not ensure contraception and is contraindicated in pregnancy, in breastfeeding, in undiagnosed abnormal vaginal bleeding, and in hypersensitivity to GnRH or its analogs.
• Intranasal delivery is a formulation achievement, not a property of the molecule in general. Systemic bioavailability from the approved spray is low (mean 2.8%) and variable (1.2% to 5.6%). The label reports no significant effect of nasal congestion on bioavailability, but instructs that any nasal decongestant be used no sooner than 2 hours after a dose and that sneezing during or just after dosing be avoided because it may impair absorption. The clinical results belong to a specific preserved solution delivered by a metered pump; powder reconstituted and administered by any other route has no supporting human data.
• The pediatric evidence is older and mostly uncontrolled. The CPP indication rests on open-label series and label-reported program data, and the class consensus statement is explicit that adult-height benefit is well established only in early-onset cases. Nafarelin is now used far less often for CPP than depot leuprolide, triptorelin, or histrelin implants, because multiple daily nasal doses depend on adherence that the label itself flags as a cause of inadequate suppression.
• Naming and class confusions. Nafarelin is a GnRH agonist that suppresses the axis through desensitization, not a GnRH antagonist (cetrorelix, ganirelix, elagolix, relugolix), which block the receptor directly without an initial flare. It should not be confused with gonadorelin (native GnRH, used diagnostically and in pulsatile form) or with buserelin, a different nasal GnRH agonist that is approved in Europe and Canada but not in the United States. The development code RS-94991 and the chemical shorthand [D-Nal(2)6]GnRH or [D-Nal(2)6]LHRH refer to the same molecule.