Cough suppressants may act centrally on the brain or locally on the respiratory tract to suppress the cough reflex. Cough suppressants include dextromethorphan (DXM), noscapine, ethyl morphine and codeine. Expectorants thin the mucus that blocks the air tubes leading to the lungs. This makes the mucus easier to cough up. The most common expectorant is Guaifenesin.