One dose of Mucinex Fast-Max adult severe cold liquid starts to work with the mucus busting power of Mucinex.Mucinex Fast-Max adult severe cold liquid contains acetaminophen, pain reliever and fever reducer; dextromethorphan HBr, cough suppressant; Guaifenesin, expectorant; phenylephrine HCl, nasal decongestant. Use for relief of headaches and fevers, controlling cough, relieving nasal and chest congestion, and thins and loosens mucus.