Acetylcysteine-- also known as N-acetylcysteine or N-acetyl-L-cysteine (NAC), is a medication used to treat paracetamol (acetaminophen) overdose and to loosen thick mucus such as in cystic fibrosis or chronic obstructive pulmonary disease. It is available by intravenous, by mouth, or inhaled as a mist. Common side effects include nausea and vomiting when taken by mouth. The skin may occasionally become red & itchy with either form. A non immune type of anaphylaxis may also occur.