Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take Montelukast.

Asthma attacks and asthma control: The effectiveness of montelukast in treating acute asthma attacks has not been established. You should not use it to treat an acute asthma attack – have your rescue medication ready in case of an acute attack. Do not stop taking montelukast without consulting your doctor. For Montelukast to be effective, it is important to take it regularly on a daily basis, even if you feel your asthma is under control, unless otherwise directed by your doctor.

If you feel your asthma symptoms are not improving or are getting worse while taking Montelukast, contact your doctor. If your asthma is made worse by acetylsalicylic acid (Asa), do not take ASA or other nonsteroidal anti-inflammatory medications (NSAIDS; e.g., Ibuprofen, Ketoprofen, Naproxen). If your asthma is made worse by exercise, continue to use the medications your doctor has prescribed before exercise.

Behaviour changes: Some people have reported changes in behaviour associated with taking montelukast. There have been occasional reports of aggressive behaviour or hostility, anxiousness, disorientation, decreased memory, sleep disturbances, or suicidal thoughts and behaviour. If you experience any of these effects or notice them in a family member who is taking Montelukast contact your doctor as soon as possible.

Depression: Montelukast has been associated with mood swings and symptoms of depression. If you have depression or a history of depression, discuss with your doctor how Montelukast may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Montelukast, and whether any special monitoring is needed.

If you experience symptoms of depression such as poor concentration, changes in weight, changes in sleep, decreased interest in activities, or notice them in a family member who is taking Montelukast, contact your doctor as soon as possible.

Phenylketonuria: The chewable tablet form of Montelukast contains aspartame, an artificial sweetener which contains phenylalanine. The 4 mg chewable tablet contains 0.674 mg of phenylalanine, and the 5 mg chewable tablet contains 0.842 mg. People with phenylketonuria are unable to break phenylalanine down to get rid of it. If you have phenylketonuria, talk to your doctor about other alternatives.

Liver function: Liver disease or reduced liver function may cause Montelukast to build up in the body, causing side effects. The safety of using montelukast for people with severely reduced liver function has not been established. If you have reduced liver function, discuss with your doctor how Montelukast may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Montelukast, and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Pregnancy: Montelukast should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Montelukast, contact your doctor immediately.

Breast-feeding: It is not known if montelukast passes into breast milk. If you are a breast-feeding mother and are taking Montelukast, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of montelukast have not been established for children under 2 years old. Montelukast can be used to treat asthma for children aged 2 years and older and to treat seasonal allergies for adolescents 15 years and older.