Acetaminophen is a medication used to treat pain and fever.  It is typically used for mild to moderate pain relief.  It is also used for more severe pain such as pain after surgery.  Effects last between two and four hours. It is generally safe at recommended doses. 

Too high dose can result in liver failure.  

It appears to be safe during pregnancy and when breastfeeding.  In those with liver disease, it may still be used, but in lower doses.  It is classified as a mild anagesic.  It does not have significant anti-inflammatory activity and how it works is not entirely clear.  It is commonly used in USA and in Europe.