I 'v taken herb which is called pure nac and every time i take capsule it gives me a little stomachache , can you explain why is it happening ?

Why taking?: Pure nac probably refers to N-acetyl-L-cysteine (nac), a free radical scavenger used in the body. It is used is certain medical situations (tylenol (acetaminophen) overdose, for example), but there really is not much evidence taking this as a supplement helps someone. If you are having stomach irritation from it, it may be causing more harm than good.