N-acetylcysteine (NAC) is a medication and supplement that serves as a precursor to the amino acid cysteine. It is commonly used to help replenish levels of glutathione, a powerful antioxidant in the body. NAC is often prescribed to treat acetaminophen overdose and to support lung health in conditions like chronic obstructive pulmonary disease (COPD). In addition to its medical uses, NAC is also popular as a dietary supplement for its potential benefits in promoting overall health. Some studies suggest it may help reduce symptoms of anxiety and improve mental clarity, although more research is needed to confirm these effects.