Synarel
Evidence Grade A — Regulatory approved. 270 published studies. 2 registered clinical trials.
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Nafarelin (sold as Synarel) is a hormone-suppressing medication delivered as a nasal spray — making it the only treatment in its class that avoids injections or implants entirely. It is used for endometriosis and central precocious puberty (early puberty in children), requiring two sprays per day. For people who strongly prefer to avoid needles, it offers a meaningful alternative.
270 published studies: 223 human, 28 animal, 32 in-vitro, 29 reviews
Nafarelin is marketed as Synarel (approved 1990) for endometriosis and central precocious puberty. It requires administration as one spray in each nostril twice daily — a higher frequency than injectable alternatives but avoids needles entirely, which can be a significant advantage for some patients, particularly children.
Clinical trials showed symptom improvement in 75–92% of endometriosis patients. However, absorption can be affected by nasal congestion or concurrent use of nasal decongestants, which can be a practical limitation. As with all GnRH agonists, prolonged use leads to bone density loss, and treatment for endometriosis is typically limited to six months. Nafarelin occupies a niche for patients who prefer non-injectable hormone suppression, though it has become less commonly prescribed as longer-acting depot injections and oral alternatives have become available.
Nafarelin works through the same GnRH agonist mechanism as injectable treatments like leuprolide — continuous exposure shuts down the body's sex hormone production after an initial brief surge. The key difference is its route of delivery: nafarelin is absorbed through the nasal lining, reaching the bloodstream without any needles. While only about 2–3% of the dose is absorbed this way, this is enough to produce full therapeutic hormone suppression.
Clinical trials showed symptom improvement in 75–92% of endometriosis patients. However, the twice-daily nasal spray schedule creates compliance challenges — missed doses and nasal congestion can both reduce effectiveness. This is a significant practical limitation compared to depot injections that work for one to six months from a single administration. Nafarelin has been largely overtaken by longer-acting injectable formulations (leuprolide, triptorelin) and the histrelin implant, which provide more reliable hormone suppression without depending on daily patient compliance. It remains available as a needle-free option for patients who cannot tolerate injections, but is no longer commonly prescribed.
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Histrelin is available as Supprelin LA for central precocious puberty (approved 2007). The Vantas implant for prostate cancer was approved in 2004 but discontinued in 2021. The implant requires a minor surgical procedure for insertion and removal/replacement each year. Supprelin LA's main clinical advantage is its 12-month duration — the longest of any GnRH agonist — which is particularly valuable in paediatric patients where treatment compliance over years is important. Clinical studies demonstrated effective suppression of puberty markers in over 97% of patients. The implant has also seen significant off-label use in gender-affirming care as a puberty blocker, where its annual dosing schedule offers practical benefits for adolescent patients and their families.
Goserelin is marketed as Zoladex by AstraZeneca, available as 3.6 mg monthly and 10.8 mg three-monthly subcutaneous implants. First approved in 1989, it is used in advanced prostate cancer, premenopausal breast cancer, endometriosis, and for thinning the uterine lining before surgical procedures. Goserelin achieves castrate-level testosterone suppression (below 50 ng/dL) within two to four weeks. Its unique implant delivery system means there is no liquid injection, reconstitution, or refrigeration required — a practical advantage in some clinical settings. Like all GnRH agonists, it causes an initial hormone flare before suppression takes effect. Goserelin holds an important niche in breast cancer treatment, where it is used to suppress ovarian function in premenopausal women with hormone-receptor-positive disease, often in combination with aromatase inhibitors.
Elagolix is marketed as Orilissa for endometriosis pain (approved July 2018) and as a component of Oriahnn for heavy menstrual bleeding from uterine fibroids (approved May 2020). Oriahnn combines elagolix with low-dose hormone add-back therapy to mitigate bone density loss. Clinical trials showed that the higher dose reduced menstrual pain in approximately 76% of patients and non-menstrual pelvic pain in about 55% at six months. The main limitation is bone density loss with prolonged use, which the add-back therapy in Oriahnn helps address. As an oral tablet taken daily, it offers a fundamentally different experience from injectable or implanted hormone treatments, though it requires consistent daily dosing. It is important to note that elagolix is not a peptide — it is included in this database because it targets the same GnRH pathway as peptide-based treatments.
