It is possible for babies to drink formula when they have a cough, especially if they are under three years old, to strengthen their immune system. Since milk is the main source of food when babies are younger, if they don’t drink milk powder, their immunity will naturally decline and their cough will be more persistent when their immunity declines. This is why babies can drink formula when they have a cough because it is caused by a respiratory infection. Drinking formula is not necessarily related to the symptoms of phlegm and cough, and it does not affect the treatment of cough.