As of 2015, the active ingredients in a 1-teaspoon dose of Cheratussin AC syrup are 10 milligrams of codeine phosphate and 100 milligrams of guaifenesin, according to DailyMed. Codeine, a cough suppressant, temporarily relieves cold-related coughs, and guaifenesin, an expectorant, helps loosen bronchial mucus for more productive coughing.
Codeine is classified as a narcotic drug, and it can be addictive. It suppresses coughs by affecting the brain signals that start the cough reflex. Guaifenesin loosens throat mucus, making it easier to cough it out through the mouth, notes Drugs.com. The combined ingredients can treat coughs due to upper respiratory infections and colds, but they do not treat asthma, smoking or emphysema-related coughs.