If you will be taking this medicine for a long time, it is very important that your doctor check you or your child at regular visits. This will allow your doctor to see if the medicine is working properly and to check for any unwanted effects.
You may be taking other medicines for asthma together with montelukast. Do not stop taking these medicines and do not reduce the dose, even if your asthma seems better, unless you or your child are told to do so by your doctor.
Talk to your doctor or get medical care right away if:
Your or your child's symptoms do not improve after using this medicine or if they become worse.
Your short-acting inhaler does not seem to be working as well as usual and you need to use it more often.
Montelukast may cause some people to be agitated, disoriented, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. Report any unusual thoughts or behaviors that trouble you or your child, especially if they are new or get worse quickly. Make sure the doctor knows if you or your child have trouble sleeping, get upset easily, or start to act reckless. Also tell the doctor if you or your child have sudden or strong feelings, such as feeling nervous, angry, restless, violent, or scared.
This medicine may increase certain white blood cells (eosinophils) and may cause systemic vasculitis. Check with your doctor right away if you have a feeling of numbness in your arms or legs, flu-like symptoms, rash, or pain or swelling of the sinuses.