N-acetylcysteine is a chemical, commonly called NAC, produced by the body that enhances the production of the enzyme glutathione, a powerful antioxidant. NAC helps boost the immune system.

NAC is used as a mucolytic ("mucus dissolving") agent to help break up the thick mucus often present in people suffering from chronic respiratory ailments. NAC is administered intravenously for the treatment of acetaminophen (paracetamol) overdose in order to protect the liver from damage.