N-acetyl-l-cysteine (NAC) is an amino acid and antioxidant. It is a precursor in the body to the critical antioxidant glutathione, which is produced intracellularly, primarily by the liver. Glutathione exerts a variety of protective effects, including detoxification and intracellular defense against oxidative stress. Substances known to reduce glutathione status are acetaminophen and alcohol.