N-Acetyl-L-Cysteine (NAC) is a derivative of the dietary amino acid l-cysteine. NAC scavenges free radicals and decreases oxidative stress produced by heavy metals to support antioxidant defence. It is also a precursor to the antioxidant glutathione, and supplemental NAC increases tissue levels of glutathione. Several animal studies suggest that NAC administration may also help to moderate the effects of mercury and cadmium accumulation in the kidneys and liver. NAC may achieve these actions in part by promoting healthy glutathione levels or protecting tissues from peroxida-tion generated by heavy metals. NAC also has a high affinity for lung tissue, which it supports through antioxidant action.