Acetylcysteine, also known as N-acetylcysteine (NAC), not to be confused with N-Acetylcarnosine, which is also abbreviated "NAC," is a medication that is used to treat paracetamol overdose and to loosen thick mucus in individuals with chronic bronchopulmonary disorders like pneumonia and bronchitis. It has been used to treat lactobezoar in infants. It can be taken intravenously, by mouth, or inhaled as a mist. Some people use it as a dietary supplement.