The Chemistry of Cough Drops


Cough drops are dissolvable tablets that are designed to soothe sore throats and stop coughing with the use of oral anesthetics. I chose to study the chemistry of cough drops because even though people use them often, how they are effective is a mystery to most. This affects my life because I have used cough drops.

Composition of ...

    • Menthol, C10H20O
    • Glucose syrup, C6H14O7
    • Sucrose, C12H22O11
    • Eucalyptol, C10H18O
    • Water, H2O

Main Chemicals, Compounds, Components

Menthol is a common active ingredient in cough drops today. Its cooling and numbing effects make it an effective oral anesthetic. The chemical can be found naturally in the leaves of mint plants, and it can also be made synthetically through hydrogenation. Menthol is believed to have been first isolated from mint leaves in Japan as long as 2000 years ago; it was not until the 1770s that western civilization was able to do so. At room temperature, menthol is a colorless solid with a crystalline structure. It is soluble in water, and highly soluble in alcohols.

Glucose syrup is one of the most common inactive ingredients used in cough drops. It is used as a sweetener, and it forms the hardened structure of the cough drop when combined with smaller amounts of other sugars. Glucose is a monosaccharide, or a simple sugar, which means it is made of a single molecule. It can be made into a syrup through the hydrolysis of a starch. Glucose syrup was first made by a Russian chemist in 1811.

Chemistry's Role

Hydrogenation is a process used to make synthetic menthol, which can be used in cough drops. Hydrogenation is a chemical reaction between molecules of hydrogen and another compound or element, often using a catalyst. The reaction breaks down double and triple bonds of hydrocarbons. This breakdown of bonds can reduce or saturate an organic compound.

Hydrolysis can be used to produce glucose syrup. Hydrolysis is the breaking of chemical bonds due to a reaction with water. Once a starch has been separated from a plant, it can be put through hydrolysis. To make glucose syrup, starch may be put through hydrolysis using various types of acids and enzymes. This means that water is added to the starch accompanied by chemicals that can also break down the sugars in the starch until glucose syrup has been made.

Background Research

Cough drops are dissolvable drops that are purposed to soothe sore throats and coughing by using anesthetics in the mouth. One of the most popular cough drop producing companies is Halls, which has been famous for its use of menthol as the acting anesthetic in their drops. The practice of using menthol in cough drops began in the 1920s and ‘30s, and Halls quickly adopted the method. The menthol used today is mostly synthetic, and it is made in labs by a process of hydrogenating thymol. Hydrogenation is the chemical reaction between hydrogen molecules and another chemical compound which can saturate or reduce an organic compound. Halls cough drops are primarily comprised of menthol, glucose syrup, sucrose, water, and eucalyptus oil.


About the Author

Marcos Lopez is a junior at Billings Senior High School. He enjoys learning new things and how they relate to the world around him. After high school, he plans on attending the University of Montana to study archaeology. Marcos is active in Senior High’s Native American Club, and he leads the school district’s Soaring Eagle Singers drum group for indigenous students in the community.