Singulair Side Effects

Generic Name: montelukast

Note: This page contains side effects data for the generic drug montelukast. It is possible that some of the dosage forms included below may not apply to the brand name Singulair.

It is possible that some side effects of Singulair may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to montelukast: oral packet, oral tablet, oral tablet chewable

As well as its needed effects, montelukast (the active ingredient contained in Singulair) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking montelukast, check with your doctor immediately:

Less common
  • Abdominal or stomach pain
  • bloody nose
  • flu-like symptoms
  • general feeling of discomfort or illness
  • headache
  • joint pain
  • pain or tenderness around the eyes and cheekbones
  • shortness of breath or troubled breathing
  • sweating
  • tightness of the chest
  • trouble with swallowing
  • unusual tiredness or weakness
  • Pus in the urine
Incidence not known
  • Agitation
  • anxiety
  • attempts at killing oneself
  • breathing problems
  • confusion about identity, place, and time
  • constipation
  • fast, irregular, pounding, or racing heartbeat or pulse
  • feeling sad or empty
  • hives or welts
  • indigestion
  • itching, puffiness, or swelling of the eyelids or around the eyes, face, lips, or tongue
  • lack of appetite
  • pains in the stomach, side, or abdomen, possibly moving to the back
  • redness of the skin
  • shaking or trembling of the hands or feet
  • trouble with concentrating
  • unable to sleep
  • unpleasant breath odor
  • upper right abdominal or stomach pain
  • vomiting of blood
  • yellow eyes or skin

Some montelukast side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common
  • Acid or sour stomach
  • belching
  • blurred vision
  • change in near or distance vision
  • dental pain
  • earache
  • heartburn
  • lack or loss of strength
  • pain
  • skin rash, encrusted, scaly and oozing
  • stomach discomfort, upset, or pain
Incidence not known
  • Burning, crawling, itching, numbness, prickling, “pins and needles”, or tingling feelings
  • dreams that are unusual
  • increased tendency to bleed
  • large, flat, blue or purplish patches on the skin
  • muscle aching or cramping
  • sleepiness
  • swollen joints

For Healthcare Professionals

Applies to montelukast: oral granule, oral tablet, oral tablet chewable

Nervous system

Nervous system side effects have included headache (18% to 20%) and dizziness (2%). Isolated and rare reports of somnolence have been associated with the use of higher than recommended doses. Seizures have been reported very rarely. Paresthesias, hypoesthesia, and drowsiness and have been reported in postmarketing experiences.


Respiratory system side effects have included influenza (4%), cough (3%), and nasal congestion (2%). In some studies, upper respiratory tract infection (28%) and worsened asthma (4% to 11%) were associated with the use of this drug. However, many patients with asthma have some or all of these symptoms, and a causal relationship has not been proven. Rhinorrhea, sinusitis, otitis, influenza, epistaxis, and pneumonia have also been reported.
Postmarketing reports have included thoracic and mediastinal disorders.


Gastrointestinal side effects have included abdominal pain, dyspepsia, or infectious gastroenteritis in up to 3% of patients. Diarrhea has been associated with the use of higher than recommended doses.
Postmarketing reports have included vomiting.


In general, montelukast (the active ingredient contained in Singulair) is well tolerated. Asthenia, fatigue, or fever has been associated with the use of this drug in approximately 2% of patients. Varicella has also been reported.


Dermatologic side effects have included rash, eczema, urticaria, and dermatitis. Postmarketing experience has included erythema multiform.
Postmarketing reports include Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN).

Churg-Strauss syndrome has been reported in association with montelukast therapy.


Hepatic side effects have included elevated hepatic serum transaminases in approximately 2% of patients. Pancreatitis has been reported very rarely. Jaundice with elevated liver enzymes are described in a 42 year old man several months after starting montelukast (the active ingredient contained in Singulair) therapy. Serum enzymes completely normalized 4 months after drug withdrawal.

Postmarketing experience has reported rare cases of cholestatic hepatitis, hepatocellular liver injury and mixed pattern liver injury.


Other side effects have included isolated cases of Churg-Strauss syndrome, a rare systemic vasculitis associated with asthma.

Churg-Strauss syndrome is a rare granulomatous eosinophilic condition that involves the upper and lower airways and manifests as rhinitis, sinusitis and asthma. If untreated the syndrome may progress to systemic vasculitis, peripheral neuropathy and potentially fatal cardiac complications. In most cases, the condition emerged during withdrawal of oral corticosteroid therapy. A causative role for leukotriene receptor antagonists has not been ruled out.


Musculoskeletal side effects have included myalgia, muscle cramps, and muscle aches. Postmarketing experience has reported arthralgia.


Hematologic side effects have included increased bleeding tendencies and bruising. Thrombocytopenia has also been reported.


Ocular side effects have included conjunctivitis.


Psychiatric side effects have included agitation including aggressive behavior and hostility, anxiousness, dream abnormalities and hallucinations, depression, insomnia, irritability, restlessness, suicidal thinking and behavior (including suicide), and tremor.
Postmarketing reports include disorientation, insomnia, and somnambulism.


Hypersensitivity side effects have included anaphylaxis, erythema nodosum, pruritus, urticaria, and very rarely hepatic eosinophilic infiltration. Postmarketing reports have included angioedema.


Postmarketing reports have included palpitations and edema.

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