GnRH agonist · endometriosis, puberty
A synthetic version of gonadotropin-releasing hormone (GnRH), the brain signal that starts the reproductive hormone chain. Given as a nasal spray branded Synarel, it is used to manage endometriosis in adult women and early (central precocious) puberty in children.
GnRH is normally released from the hypothalamus in pulses, telling the pituitary to release LH and FSH, which in turn drive the ovaries and testes to make estrogen and testosterone. Nafarelin is a ten-amino-acid GnRH analog with one building block swapped for a synthetic one, which makes it a potent agonist. At first it over-stimulates the pituitary, briefly raising LH, FSH and sex hormones (a flare). With continued use, the constant signal desensitizes the pituitary, so sex hormone production falls to low levels within about four weeks. In endometriosis, low estrogen lets the estrogen-dependent lesions shrink; in precocious puberty, it pauses pubertal development until treatment stops.
In a double-blind randomized trial, 213 women with laparoscopy-confirmed endometriosis received six months of nafarelin nasal spray at one of two dose levels or oral danazol2. More than 80% in each group had less disease on repeat laparoscopy, scores fell similarly across groups, and the share reporting severe pain dropped from about 40% to 5 to 10%. Nafarelin avoided danazol's unfavorable cholesterol changes but caused more hot flashes and lower libido2. The label reports that six months of treatment lowered vertebral bone density, with only partial recovery afterward1.
In 155 children with central precocious puberty treated for an average of more than three years, it suppressed pubertal hormones to prepubertal levels and slowed growth and bone maturation; suppression reversed in all 69 children followed for a year after stopping1.
First FDA-approved in 1990 as Synarel nasal spray, now from Pfizer. The current label covers management of endometriosis in adult women and treatment of central precocious puberty in children of both sexes.
In adults, most effects stem from low estrogen: hot flashes, vaginal dryness, headaches, mood changes, reduced libido, acne, muscle pain, reduced breast size, nasal irritation, and bone density loss. In children, early effects reflect the initial flare (acne, temporary breast enlargement, vaginal bleeding, emotional lability). Warnings include depression, seizures, pseudotumor cerebri in children, severe skin reactions, pituitary apoplexy, and ovarian cysts early in treatment. It must not be used during pregnancy or breastfeeding1.
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