Hi.. Can understand your concern.. As per your complain cough drops mostly contain Menthol which can be taken to relieve sore throat and reileve in cough and cold but if taken in excess can have toxicity and can also lead to irritation of mucosa.. Along with it the sugar present in cough drops can cause infection over tongue as well as other parts of mouth due to continuous sugar source present in mouth which can lead to bacterial growth leading to infection and inflammation.. The white layer can also occur due to infection and deposit of remnants of cough drops on tongue. Another thing I would like to tell you that make sure that white covering is not as a result of fungal infection on tongue leading to white patches and burning of tongue. If you find any doubt about fungal infection consultation with an oral pathologist needs to be done. If not so just avoid taking the cough drops and take cool liquids and such on ice to relieve burning and pain in tongue. Application of numbing gels can help half an hour before taking food to avoid pain. Avoid spicy and hot food to avoid further irritation of tongue.. It will hopefully heal in a two to three days.. Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora