Cough drops help relieve nagging coughs and cavity-causing dry mouth. Check the label to avoid cough drops and liquid cold medications containing fructose or corn syrup. These sugars can lead to cavities, especially if you keep them in your mouth for a long time. Choose sugar-free lozenges and medications in tablet form instead. If you give children 4 years or older liquid cold medication sweetened with sugar, have them rinse with water afterward and brush their teeth if given right before bedtime or a nap.