NAC is safe and effective at reasonable doses through oral supplementation. The most common side effects from oral NAC include nausea, vomiting, and diarrhea.[1][2] Due to the sulfur content of NAC, supplements can have an unpleasant rotten-egg odor.[1] When inhaled, NAC may cause cough and bronchospasm (constriction of the airways).[3]
NAC toxicity mostly occurs in clinical settings, with one case of overdose occurring due to an error in the preparation of an IV solution. An excessive dose of NAC in a short time period can cause red blood cell breakdown (hemolysis), low blood platelet count (thrombocytopenia), kidney failure, and possibly death.[4]