N-acetylcysteine (NAC) is a mucolytic agent and antioxidant derived from the amino acid cysteine, primarily used to treat acetaminophen overdose and to alleviate symptoms of chronic obstructive pulmonary disease (COPD) by thinning mucus. Its clinical significance lies in its ability to replenish glutathione levels, thereby protecting against oxidative stress and cellular damage. A key association is its use in preventing renal injury during contrast media administration, highlighting its protective role in high-risk patients.