Guaifenesin and codeine is a prescription medication that's used to treat coughing, chest congestion, and throat irritation caused by cold, flu, and other respiratory illnesses. Guaifenesin is an expectorant, which helps loosen mucus in the lungs, making it easier to cough up mucus. Codeine is a narcotic cough suppressant that works in the brain to help reduce the cough reflex. Guaifenesin and codeine is available as a tablet or as a liquid, which are both taken by mouth with plenty of fluids. It's very important to take this medication exactly as prescribed by your doctor and only for the length of time prescribed. Serious side effects or even dependency or abuse may occur with prolonged use. Guaifenesin and codeine are the generic names for the active ingredients contained in several medications, including Robitussin-AC, Brontex, Guiatuss AC, Cheratussin AC, and others, including generic versions. Talk to your doctor to determine whether guaifenesin and codeine is right for you.