Why alcohols are used in cough …

Most cough syrups contain menthol and natural extracts, for carminative and antitussive actions. These substances are water-insoluble and so alcohol is used as a solvent. Alcohol is miscible in all proportions with many of the syrups and so is the solvent of choice for many preparations. This property is rendered by its R-OH (hydroxyl) group which increases miscibility via inter molecular hydrogen bonding with solute particles. This enables the syrup to be absorbed easily by the body.

In addition syrups are mainly made of gels which in turn contain a liquid (as dispersed phase) and a solid (as dispersion medium). In them, alcohols play the role of stabilizers by preventing coagulation of solute particles during storage.

Alcohol serves as a preservative and stabilizer in syrups. Alcohols are good sedatives and hypnotics as they depress the activity of the central not nervous system and lead to sleep. As a result they reduce the irritation in the throat and also reduce coughing.