Singulair side effects: what you should know
Taking Singulair (montelukast) can help with asthma and allergies, but like any medicine it comes with side effects. Most people tolerate it fine, yet some notice headaches, stomach upset, or sleep problems. Other reactions are rare but serious — and you should know how to spot them fast.
Common and mild side effects
The usual side effects are often short-lived and easy to manage. You might get a headache, stomach pain, diarrhea, or feel a bit dizzy. Some people report cough, nasal congestion, or fatigue. If these symptoms are mild, they often improve after a few days to weeks. Drink water, rest, and keep track of symptoms so you can tell your doctor if they stick around.
If a mild side effect bothers your daily life — for example, ongoing headaches or persistent stomach pain — don’t ignore it. Call your prescriber to discuss changing dose, switching medicines, or trying a different approach for allergy or asthma control.
Serious side effects and when to act
There’s an FDA warning about montelukast and mood or behavior changes. Some people develop anxiety, agitation, depressed mood, hallucinations, or thoughts of self-harm. These are uncommon but serious. If you or someone you care for starts acting very different, becomes unusually irritable, withdraws socially, or mentions hurting themselves, stop the medicine and call your doctor or emergency services right away.
Other rare but serious reactions include allergic responses (rash, swelling, breathing trouble) and sudden changes in breathing. If you see signs of an allergic reaction — hives, face or throat swelling, trouble breathing — get emergency help immediately.
Don’t make big changes without talking to your clinician. If symptoms are severe or life-threatening, emergency care is the right call. For less urgent but worrying signs, ask for a same-day appointment or phone advice.
When weighing risks, remember that untreated asthma can be dangerous too. Montelukast might still be the right choice if it controls your breathing and allergy issues better than alternatives. Ask your doctor to review benefits versus risks based on your personal health and options.
Simple tips: monitor mood and sleep after starting montelukast, keep a symptom diary, and include caregivers when the patient is a child or older adult. Report serious side effects to your healthcare provider and local health authority so others can benefit from that information.
If you want other ways to manage asthma or allergies, talk about inhaled corticosteroids, nasal steroid sprays, or antihistamines. These may avoid the specific mood-related risks linked to montelukast.
Bottom line: watch for head-to-toe changes — especially mood or behavior shifts — and contact your provider if anything feels wrong. It’s better to check early than wait for a problem to get worse.
