N-Acetyl-L-Cysteine, or N-A-C, is an acetylated form of the amino acid cysteine. Cysteine is the most important precursor to glutathione (GSH), the most critical antioxidant produced in the body. It has been used for over 30 years for respiratory health, providing relief to those suffering from chronic respiratory conditions such as chronic bronchitis.
Management must be multifactorial as there are many symptoms of chronic bronchitis such as:
Cough: persistent and/or productive
Wheezing 
Shortness of breath (especially with physical activity)
Chest tightness (discomfort in your chest)
Tiredness
 
AOR Advantage
As the precursor for the important antioxidant glutathione, acetylated cysteine is thought to be more easily absorbed for certain groups.