Benadryl syrup is a medication that is used for the treatment of coughs and colds. It provides relief from symptoms such as runny nose, sneezing, sore throat, and watery eyes. The active ingredients of Benadryl syrup are diphenhydramine, ammonium chloride, and sodium citrate. Benadryl syrup works by blocking the effects of allergic chemicals and providing relief from allergic symptoms like a runny nose and watery eyes. This medicine also thins the mucous and makes it easier to cough out.