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Synarel Side Effects

Generic name: nafarelin

Medically reviewed by Last updated on Oct 14, 2023.

Note: This document contains side effect information about nafarelin. Some dosage forms listed on this page may not apply to the brand name Synarel.

Applies to nafarelin: nasal spray.

Serious side effects of Synarel

Along with its needed effects, nafarelin (the active ingredient contained in Synarel) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking nafarelin:

More common

For adults (female)

  • Breast enlargement
  • light vaginal bleeding between regular menstrual periods, called spotting
  • longer or heavier menstrual periods
  • vaginal bleeding between regular menstrual periods, called breakthrough bleeding

For children (male)

  • Body odor
  • growth of pubic hair

For children (female)

  • Body odor
  • breast enlargement
  • growth of pubic hair
  • light vaginal bleeding between regular menstrual periods, called spotting
  • longer or heavier menstrual periods
  • vaginal bleeding between regular menstrual periods, called breakthrough bleeding

Less common

  • Chest pain
  • rash, hives or welts, itching
  • redness of the skin

Less common or rare

For adults (female)

  • Fast or irregular heartbeat
  • numbness or tingling of the hands or feet
  • pain in the eyes or joints
  • patchy brown or dark brown discoloration of the skin
  • pelvic bloating or tenderness
  • unexpected or excess milk flow from the breasts
  • unusual tiredness or weakness

Incidence not known

For adults (female)

  • Cough
  • difficulty with speaking
  • dizziness or lightheadedness
  • double vision
  • fainting
  • fast heartbeat
  • inability to move the arms, legs, or facial muscles
  • inability to speak
  • nausea
  • pain or discomfort in the arms, jaw, back, or neck
  • pain, redness, or swelling in the arm or leg
  • slow speech
  • sweating
  • trouble breathing
  • vomiting
  • yellow eyes or skin

Incidence not known

  • Anxiety or mental depression
  • blurred or double vision
  • change in ability to see colors, especially blue or yellow
  • changes in vision
  • cold, clammy, or pale skin
  • confusion
  • discouragement
  • eye pain
  • feeling sad or empty
  • headache
  • irregular heartbeats
  • irritability
  • lack of appetite
  • loss of interest or pleasure
  • nightmares or unusually vivid dreams
  • seizures
  • slow heart rate
  • trouble concentrating
  • trouble sleeping
  • vomiting
  • weakness

Other side effects of Synarel

Some side effects of nafarelin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For adults (female)

  • Acne
  • dandruff
  • hot flashes
  • increase or decrease in sexual desire
  • increased hair growth, often abnormally distributed
  • mood swings
  • muscle pain
  • oily skin
  • pain during sexual intercourse
  • rapid weight gain
  • reduced breast size
  • stopping of menstrual periods
  • swelling of the feet or lower legs
  • vaginal dryness

For children (male)

  • Acne
  • dandruff
  • mood swings
  • oily skin

For children (female)

  • Acne
  • dandruff
  • hot flashes
  • mood swings
  • oily skin

Less common or rare

For adults (female)

  • Breast pain
  • headache (mild and transient)
  • irritated or runny nose
  • mental depression (mild and transient)

For children (male)

  • Irritated or runny nose

For children (female)

  • Irritated or runny nose
  • white or brownish vaginal discharge

For Healthcare Professionals

Applies to nafarelin: nasal spray.


Very common (10% or more): Hot flashes/hot flush (up to 90%)

Common (1% to 10%): Chest pain, edema, hyper/hypotension

Frequency not reported: Palpitations

Postmarketing reports: Arterial thromboembolism, deep vein thrombosis, myocardial infarction, venous thromboembolism[Ref]

Hot flashes occurred commonly in adult women who were treated for endometriosis. Approximately 3% of children developed transient hot flashes.[Ref]


Very common (10% or more): Decreased libido (up to 23%), emotional/affect lability (up to 15%)

Common (1% to 10%): Depression, increased libido, insomnia

Postmarketing reports: Aggression, anger, impatience, irritability, suicidal ideation, suicide attempt[Ref]


Very common (10% or more): Vaginal dryness (up to 19%)

Common (1% to 10%): Transient breast enlargement, breast atrophy/decreased breast size, vulvovaginal dryness, artificial menopause, uterine hemorrhage, vaginal bleeding, white/brown vaginal discharge

Uncommon (0.1% to 1%): Ovarian cyst

Frequency not reported: Ovarian hyperstimulation syndrome[Ref]

Nervous system

Very common (10% or more): Headache (up to 18%)

Common (1% to 10%): Paresthesia

Frequency not reported: Migraines

Postmarketing reports: Convulsions, stroke, transient ischemic attack[Ref]


Very common (10% or more): Acne (up to 14%)

Common (1% to 10%): Transient increase in pubic hair, body odor, seborrhea, pruritus, rash, urticaria, hirsutism

Uncommon (0.1% to 1%): Alopecia[Ref]


Common (1% to 10%): Rhinitis, dyspnea, nasal irritation

Frequency not reported: Shortness of breath

Postmarketing reports: Interstitial pneumonitis, pulmonary embolism, pulmonary fibrosis[Ref]


Common (1% to 10%): Myalgia, decreased bone mineral density

Uncommon (0.1% to 1%): Arthralgia

Postmarketing reports: Arthritic symptoms[Ref]


Common (1% to 10%): Estrogen deficiency

Frequency not reported: Pituitary enlargement/asymmetry/pituitary gland changes (size and shape)

Postmarketing reports: Pituitary apoplexy[Ref]


Common (1% to 10%): Increased/decreased weight

Frequency not reported: Increased serum alkaline phosphatase, increased total cholesterol/triglycerides[Ref]


Common (1% to 10%): Drug hypersensitivity[Ref]


A patient with congenital adrenal hyperplasia developed an adrenal rest tumor 8 months after discontinuing treatment; however, correlation to treatment is unlikely.

Pituitary gland adenomas have been observed in a few children receiving treatment; however, the relationship to treatment is unknown.[Ref]

Frequency not reported: Adrenal rest tumor of the testis, pituitary gland adenoma[Ref]


Frequency not reported: Increased AST/ALT, serious liver injury[Ref]


Frequency not reported: Blurred vision[Ref]


Postmarketing reports: Crying


1. Product Information. Synarel (nafarelin). Roche Laboratories. 2001.

2. Product Information. Synarel (nafarelin). Searle.

3. Product Information. Synarel (nafarelin). Pfizer U.S. Pharmaceuticals Group. 2022.

4. Cerner Multum, Inc. UK Summary of Product Characteristics.

5. Cerner Multum, Inc. Australian Product Information.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.