N-Acetyl L-Cysteine is used by the body to manufacture the detoxifying substances glutathione and glutathione peroxidase which protect the body from free radicals and toxins. Cystiene is also considered a preventative or antidote for some of the negative effects of alcohol, including hangover and liver damage. It has a counteractive effect on the poisonous effects of acetaldehyde which is a by-product of alcohol and responsable for most of the negative effects and long term damage to the liver.