Acetylcysteine

Acetylcysteine, also known as "N"-acetylcysteine (NAC), is a medication. It is used to treat paracetamol overdose and to loosen thick mucus when someone has pneumonia or bronchitis or other (similar) chronic bronchopulmonary disorders. 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.
Chemistry.
Acetylcysteine is the "N"-acetyl derivative of the amino acid -cysteine. It is a precursor, when the human body makes the antioxidant glutathione.