Acetylcysteine rINN
International Nonproprietary Name
An International Nonproprietary Name is the official nonproprietary or generic name given to a pharmaceutical substance, as designated by the World Health Organization...

 (icon), also known as N-acetylcysteine or N-acetyl-L-cysteine (abbreviated NAC), is a pharmaceutical drug and nutritional supplement used primarily as a mucolytic agent
Mucolytic agent
Mucokinetics are a class of drugs which aid in the clearance of mucous from the airways, lungs, bronchi, and trachea. Such drugs can be further categorized by their mechanism of action.* expectorants* mucolytic agents...

 and in the management of paracetamol
Paracetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...

 (acetaminophen) overdose. Other uses include sulfate repletion in conditions, such as autism, where cysteine and related sulfur amino acids may be depleted.

Acetylcysteine is a derivative of cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...

; an acetyl group is attached to the nitrogen atom.