A doctor prescribed a 3 months old baby desloratadine 1.25 mg .. isn't this dangerous ??

Never use it: I don't find using antihistamines, even relatively safe ones like this, appropriate in a 3 month old.Most of their congestion is driven by narrow nasal passages common to small babies and the irritants in the air they are exposed to.Eliminate the fragrances/dust/smoke/cleaning fumes etc. and they usually get better.Using saline nasal wash can also improve congestion.

Please don't use: Please don't use this medication in a 3 month old. This medicine is primarily used for allergies, and a 3 month old is to young to have developed seasonal/environmental allergies. If the baby has a cough or runny nose, these symptoms are not due to allergies! It is likely a viral infection. There is no safe OTC medicine to use in babies this young, except Tylenol for fever. Try bulb suction.