N-Acetyl-l-Cysteine (NAC) is a derivative of the dietary amino acid l-cysteine. NAC has a high affinity for lung tissue, which it supports through mucolytic and antioxidant action. By disrupting disulfide bonds, NAC thins mucus. It is a powerful free radical scavenger and thus supports the bodys natural defense system. NAC supports tissue levels of glutathione, a key component of the antioxidant defense system. It also has the ability to help chelate heavy metals.Pure Encapsulations recommends between 600-1800mg per day, in divided doses, between meals. PureEncapsulations NAC capsules come in both 600 and900 mg capsules.