When treating a cough with cough syrups, it is important to consider the active ingredients as well as both the taste and form in which the medication is taken. Cough and cold are often accompanied by a sore throat, which leads to painful swallowing. Because liquids are easy to swallow, most people with cough associated with a cold prefer a liquid dosage form, according to consumer surveys. This may be because the active ingredients are already dissolved and ready to work and that syrups can be soothing.
The soothing nature of cough syrups comes from the properties and characteristics of the liquid itself. One of those properties is the viscosity or “thickness” of the liquid. Fluids with high viscosity pour and flow more slowly that those with low viscosity. A high viscosity is an advantage for a cough medication because, just as a viscous liquid like gravy can coat the surface of a spoon, a viscous cough syrup can coat the surface of the throat. A cough syrup with a long residence time can linger in the throat and may help to reduce coughing by increasing moisture.
A second important property of cough syrups is taste. The sensations caused by sweet, sour, and spicy tastes are known to promote salivation (secretion of saliva).1 The increase in salivation caused by sweet-tasting syrups can help reduce the discomfort associated with an irritated throat. There is even recent evidence that sweet-tasting substances can directly lower sensitivity to cough.3 Further, the viscosity of cough syrups may help to prolong the sweet taste in the mouth.2