Bleeding disorder. N-acetyl cysteine might slow blood clotting. There is concern that N-acetyl cysteine might increase the risk of bruising and bleeding in people with bleeding disorders.
Surgery. N-acetyl cysteine might slow blood clotting. This might increase the risk of bleeding during and after surgery. Stop taking N-acetyl cysteine at least 2 weeks before a scheduled surgery.
Wow.
From the Webmd article: