Now N-Acetyl Cysteine 1000mg Vegetarian Tablet is a stable form of the non-essential amino acid cysteine. It is a sulphur-containing amino acid that acts as a stabiliser for the formation of protein structures and is also necessary for the formation of glutathione. Molybdenum and selenium are essential trace minerals that facilitate the production of several important enzymes. Black spots may appear in NAC because of a normal oxidative reaction, but the product is safe to consume. These spots are not mould or any other micro-contamination. Micro-testing has been performed to assess product safety.