Is nafarelin FDA-approved, and what does the research show?

What is nafarelin?

Nafarelin is a prescription medicine that lowers the sex hormones made by the ovaries and testes ¹. It is not a wellness, weight-loss or performance peptide, and its label lists no such use ¹. It is a decapeptide, a chain of ten amino acids, the building blocks of proteins ¹. The label calls it "a synthetic analog of the naturally occurring gonadotropin-releasing hormone (GnRH)" ¹. An analog is a modified copy of a natural molecule.

GnRH is the hormone that makes the pituitary, a gland at the base of the brain, release two messenger hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) ¹. Those two, called gonadotropins, drive the ovaries and testes to make sex hormones ¹. Nafarelin acts on that chain, and with regular use it shuts the chain down ¹.

Pfizer supplies it as Synarel, a metered spray for the lining of the nose ¹, ². Based on studies in monkeys, the label says, it "is not absorbed after oral administration" ¹.

Is nafarelin FDA-approved?

Yes. FDA approved Synarel (nafarelin acetate) nasal spray on February 13, 1990, under new drug application (NDA) 019886 ². Drugs@FDA, FDA's database of approved drugs, classes it as a new molecular entity, an active ingredient FDA had not approved before ². Its marketing status there is "Prescription" as of November 9, 2026, the date of the record's data ². It lists one nafarelin application, Pfizer's, with one product, and no over-the-counter form ².

The current label is marked "Revised: November 2025" in the version that DailyMed, the National Library of Medicine's label site, dates March 5, 2026 ¹. It gives two indications, the uses FDA has approved ¹. FDA's 1998 medical review says the endometriosis application was approved February 13, 1990, and that Synarel "is approved in the US only for endometriosis and precocious puberty" ³. The first reads: "SYNAREL is indicated for treatment of central precocious puberty (CPP) (gonadotropin-dependent precocious puberty) in children of both sexes" ¹.

CPP is early puberty driven by the pituitary's gonadotropins ¹. The label says it is suspected when signs of puberty appear "at or before the age of 8 years in girls and 9 years in boys," and are "accompanied by significant advancement of bone age and/or a poor adult height prediction" ¹. Bone age is a measure of how mature the skeleton is.

The second reads: "SYNAREL is indicated for management of endometriosis, including pain relief and reduction of endometriotic lesions" ¹. Endometriosis is a condition in which tissue like the lining of the uterus grows as implants elsewhere in the pelvis, often with pain. The label sets a limit on what is known: "Experience with SYNAREL for the management of endometriosis has been limited to women 18 years of age and older treated for 6 months" ¹.

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How does nafarelin work?

Nafarelin is an agonist, a drug that switches a receptor on, and the label calls it "a potent agonistic analog" of GnRH ¹. "At the onset of administration, nafarelin stimulates the release of the pituitary gonadotropins, LH and FSH, resulting in a temporary increase of gonadal steroidogenesis," it says ¹. Gonadal steroidogenesis is the ovaries' or testes' production of sex hormones.

Then the response fades. "Repeated dosing abolishes the stimulatory effect on the pituitary gland," the label says ¹. Sex-hormone output drops "by about 4 weeks," and tissues that depend on those hormones "become quiescent," meaning inactive ¹.

Both approved uses rest on that quiet. In women the drug "lowers serum estradiol levels," estradiol being a form of estrogen ¹.

The effect lasts only with regular use. The label warns that "irregular or incomplete daily doses may result in stimulation of the pituitary-gonadal axis," the chain from pituitary to ovaries or testes ¹. After treatment stops, normal function "is usually restored within 4 to 8 weeks" ¹.

Little of each spray reaches the blood. In adult women, blood levels peaked 10 to 40 minutes after a dose ¹. Bioavailability, the share of a dose that reaches the blood, averaged 2.8 percent ¹. The half-life, the time for half the drug to leave the blood, was about three hours ¹.

What does the research show?

The evidence level is Approved for a use, since both uses are indications on the FDA-approved label ¹. In endometriosis, nafarelin was compared with two other drugs, danazol and leuprolide ⁴, ¹. The label does not say how the trials in children were designed ¹.

Studied in people for endometriosis: a randomized trial published in February 1988 enrolled 213 women with endometriosis confirmed by laparoscopy, a keyhole examination of the pelvis ⁴. Randomized means the women were assigned to their treatments by chance. For six months they received one of two dose levels of nafarelin spray, or oral danazol, the comparison drug ⁴. The trial was double-blind: dummy sprays and dummy tablets kept patients and doctors from knowing who received which ⁴. Each of the three treatment groups in the published abstract received an active drug, nafarelin or danazol ⁴.

The disease was scored at laparoscopy before and after treatment, on the American Fertility Society's scale ⁴. Mean scores fell from 21.9 to 12.6 in the higher-dose nafarelin group and from 20.4 to 11.7 in the lower-dose group ⁴. With danazol they fell from 18.4 to 10.5 ⁴. Each fall was statistically significant, and the groups did not differ significantly from one another ⁴. "More than 80 percent of the patients in each treatment group had a reduction in the extent of disease as assessed by laparoscopy" ⁴.

Symptoms eased too. The share of women with severely painful symptoms fell from about 40 percent to between 5 and 10 percent ⁴. The share with no or minimal discomfort rose from 25 to 70 percent ⁴. The abstract gives those two figures for the trial's patients together, not group by group ⁴.

Of the 149 women who tried to become pregnant after treatment, 58, or 39 percent, succeeded, at similar rates in the three groups ⁴. On fertility the label says, "There is no evidence that pregnancy rates are enhanced or adversely affected by the use of SYNAREL" ¹. The authors concluded that nafarelin "is an effective agent for treating endometriosis and has few side effects other than hypoestrogenism," meaning low estrogen ⁴.

The label sums up the controlled studies in the same terms ¹. Six months of nafarelin "was shown to be comparable to danazol" in relieving pelvic pain, painful periods and pain during sex, and in shrinking the implants seen at laparoscopy ¹. It then adds a caution: "The clinical significance of a decrease in endometriotic lesions is not known at this time and, in addition, laparoscopic staging of endometriosis does not necessarily correlate with severity of symptoms" ¹. In "a single controlled clinical trial," the spray was also "clinically comparable to intramuscular leuprolide depot," a monthly injection, for the symptoms of endometriosis ¹.

At the label's recommended dose for endometriosis, periods stopped in about 65 percent of patients by 60 days, 80 percent by 90 days and 90 percent by 120 days ¹. Doctors call the absence of periods amenorrhea. Among women who did not become pregnant, normal cycles had returned in 4 percent one month after stopping, 82 percent at two months and all at three ¹.

At the end of treatment, 60 percent of those patients were symptom free, 32 percent had mild symptoms, 7 percent moderate and 1 percent severe ¹. Relief did not always last ¹. Of the patients who were symptom free, half remained so six months after stopping, 33 percent had mild symptoms and 17 percent moderate ¹. The label states: "The recommended duration of administration is six months. Retreatment cannot be recommended since safety data for retreatment are not available" ¹.

Studied in people for central precocious puberty: the label reports clinical trials in children, 155 of whom make up its safety data ¹. Used regularly, it says, nafarelin "suppresses LH and sex steroid hormone levels to prepubertal levels," brings "a corresponding arrest of secondary sexual development, and slows linear growth and skeletal maturation" ¹. Secondary sexual development means the body changes of puberty, such as breasts and pubic hair. A GnRH stimulation test measures how much LH the pituitary releases after a dose of GnRH. Within one month of treatment, that response fell from a pubertal to a prepubertal level ¹.

Breast development stopped or regressed in 82 percent of girls, and genital development in 100 percent of boys ¹. Pubic hair stopped or regressed in only 54 percent of children, because adrenal hormones that nafarelin does not affect largely control it ¹. Growth slowed in most children within the first year to "5 to 6 cm/year or less" ¹. "The mean predicted adult height increases," the label says, without giving a figure ¹.

The suppression reversed in all 69 children who had a year of follow-up after stopping ¹. "Semen analysis was normal in the two ejaculated specimens obtained thus far," the label says ¹. It adds, "Fertility has not been documented by pregnancies and the effect of long-term use of the drug on fertility is not known" ¹.

The label and the trial cited here report no study of nafarelin for weight loss, muscle, aging or athletic performance ⁴, ¹. The label also says safety and effectiveness for endometriosis in patients younger than 18 "have not been established" ¹.

What are the side effects?

In women, "the most frequently reported adverse reactions were those related to hypoestrogenism," the label says ¹. It lists the most frequent as "hot flashes, headaches, emotional lability, decreased libido, vaginal dryness, acne, myalgia, and reduction in breast size" ¹. Emotional lability means mood swings, and myalgia is muscle pain. Nasal irritation "occurred in about 10% of all patients who used intranasal nafarelin" ¹.

The label compares nafarelin with danazol in a bar chart of adverse events over six months, in 203 women on nafarelin and 147 on danazol ¹. Hot flashes, weight gain and weight loss are among the events charted, and the label prints no percentage for any of them ¹. In the 1988 trial, a higher percentage of nafarelin users than danazol users reported hot flashes and decreased libido ⁴. The chart's weight entries are side-effect reports from women treated for endometriosis, not the results of a weight study ¹.

At the end of treatment, no nafarelin patient had HDL cholesterol under 30 milligrams per deciliter (mg/dL), against 43 percent of danazol patients ¹. None had LDL cholesterol over 190 mg/dL, against 15 percent on danazol ¹. HDL and LDL are the two cholesterol fractions on a standard blood test. Mean total cholesterol rose significantly in both groups ¹. Triglycerides, another blood fat, were above 150 mg/dL in 12 percent of nafarelin patients and 7 percent of danazol patients ¹.

The label reports bone loss and says, "During one six-month treatment period, this bone loss should not be important" ¹. "The induced hypoestrogenic state results in a small loss in bone density over the course of treatment, some of which may not be reversible" ¹. After six months, the density of the spongy inner bone of the spine had fallen 8.7 percent on average on CT scans ¹. It was still 4.9 percent below the starting level after treatment ended ¹. The label warns that use "for longer than the recommended six months or in the presence of other known risk factors for decreased bone mineral content may cause additional bone loss" ¹.

The label has four contraindications, situations in which the drug must not be used ¹. They are "Hypersensitivity to GnRH, GnRH agonist analogs or any of the excipients in SYNAREL"; "Undiagnosed abnormal vaginal bleeding"; "Use in pregnancy or in women who may become pregnant while receiving the drug"; and "Use in women who are breast-feeding" ¹. The drug "may cause fetal harm when administered to a pregnant woman" ¹. The label says "Contraception is not insured ... by taking SYNAREL, particularly if patients miss successive doses" ¹. It adds that "patients should use nonhormonal methods of contraception" ¹.

For adults the label warns that "Depression may occur or worsen during treatment with GnRH agonists," Synarel included ¹. Ovarian cysts have been reported in the first two months, many but not all in women with polycystic ovarian disease ¹. The label says they may resolve "generally by about four to six weeks of therapy, but in some cases may require discontinuation of drug and/or surgical intervention" ¹. Among 1,509 adults in formal clinical trials, 3, about 0.2 percent, had symptoms suggesting drug sensitivity, such as rash or shortness of breath ¹.

The label says "Post-marketing reports of convulsions have been observed in patients receiving GnRH agonists," and it lists "Rarely reported serious liver injury" ¹. It also records "Cases of serious venous and arterial thromboembolism," blood clots that block veins or arteries ¹. It adds, "It is unknown if there is a causal association between the use of GnRH analogs and these events" ¹.

Rare cases of pituitary apoplexy, "a clinical syndrome secondary to infarction of the pituitary gland," have followed GnRH agonists, most within two weeks of the first dose ¹. Infarction is the death of tissue whose blood supply is cut off. Severe skin reactions "have been reported in patients receiving other GnRH agonists," the label says ¹. Ovarian hyperstimulation syndrome has been reported when Synarel was used alone in fertility treatment, which the label notes "is not an approved indication" ¹.

In children, the safety data come from 155 patients treated for 41 months on average and for as long as 80 months ¹. Reported events included acne (10 percent), transient breast enlargement (8 percent), vaginal bleeding (8 percent) and emotional lability (6 percent) ¹. The label says "initial estrogen withdrawal bleeding may occur, generally within 6 weeks after initiation of therapy" ¹.

A transient increase in pubic hair occurred in 5 percent of the children, body odor in 4 percent and seborrhea, oily and scaly skin, in 3 percent ¹. Rhinitis, a runny or stuffy nose, occurred in 5 percent, hot flashes in 3 percent and white or brownish vaginal discharge in 3 percent ¹. Symptoms suggesting drug sensitivity were reported by 2.6 percent, and about 3 percent of the children withdrew because of adverse events ¹.

For children the label carries warnings drawn from the whole GnRH agonist class ¹. "Psychiatric events have been reported in patients taking GnRH agonists," among them crying, irritability, anger and aggression ¹. The label reports "Pseudotumor cerebri (idiopathic intracranial hypertension)," a rise in pressure inside the skull, "in pediatric patients receiving GnRH agonists" ¹. It also records depression, "including rare reports of suicidal ideation and attempt," in children treated with GnRH agonists for CPP ¹. Scans during and after long-term treatment "occasionally revealed changes in the shape and size of the pituitary gland," and the label says their link to Synarel "is not known" ¹.

In sport

Nafarelin is named on the 2026 Prohibited List of WADA, the World Anti-Doping Agency ⁵. The list places it in section S2.2.1, headed "Testosterone-stimulating peptides in males" ⁵. The entry reads: "gonadotrophin-releasing hormone (GnRH, gonadorelin) and its agonist analogues (e.g. buserelin, deslorelin, goserelin, histrelin, leuprorelin, nafarelin and triptorelin)" ⁵. Section S2 as a whole is marked "PROHIBITED AT ALL TIMES (IN- AND OUT-OF-COMPETITION)" ⁵. Triptorelin, named in the same entry, has its own page in this library.

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JumpstartMD does not prescribe nafarelin. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 10, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.