<s>[INST] Hi Doctor, I have a 2 1/2 yrs old son and his nose always gets blocked during the night and he finds trouble in breathing during night.He snores as adult and finds difficult to breath. On every morning he has running nose and yellow mucus is observed. Pediatric Doctor has diagnosed and he seems not to have nasal congestion and suspecting as some allergy causing this blockage and running nose. He adviced L Montus kid one per day. Want to know whether this medicine is safe and does it have any side effects. Thanks Sriram [/INST] Hello Studies show that there is very few( not significant) side effects of montelukast even on long term use.These may be headache, indigestion, cough etc. As this problem is recurrent I would suggest you to also consult an E.N.T. specialist to rule out any local nasal problem. You can give montelukast also use nasal saline drop to relieve nasal blockade due to dried secretions. Regards </s>