More than 100 products contain acetaminophen, a common over-the-counter pain reliever that is also present in many combination prescription drugs. If several similar products are consumed at a time, a person may inadvertently take too much acetaminophen. Many preparations intended for use in children are available in liquid, tablet, and capsule form, and a parent may try several preparations simultaneously or within several hours to treat a fever or pain, not realizing they all contain acetaminophen.
Acetaminophen usually is a very safe drug even in large doses, but it is not harmless. To cause poisoning, several times the recommended dose of acetaminophen must be taken. For example, a person who weighs 150 pounds generally needs to take at least about 30 325-milligram tablets before toxic effects due to a single overdose are possible. Death is extremely unlikely unless the person takes more than 40 325-milligram tablets. Therefore, a single acetaminophen overdose that causes serious toxicity is usually not accidental.
Toxicity also may develop if multiple smaller doses are taken over time. In toxic doses, acetaminophen can damage the liver. Liver failure can follow.
Symptoms and Diagnosis
Most overdoses cause no immediate symptoms. The level of acetaminophen in the blood, measured 4 hours after ingestion, may help predict the severity of the liver damage. If the overdose is very large, symptoms develop in four stages. In stage 1 (after several hours), the person may vomit but does not seem ill. Many people have no symptoms until stage 2 (after 24 to 72 hours), when nausea, vomiting, and abdominal pain may develop. At this stage, blood tests show that the liver is functioning abnormally. In stage 3 (after 3 to 4 days), vomiting becomes worse. Tests show that the liver is functioning poorly, and jaundice (yellowing of the eyes and skin) and bleeding develop. Sometimes the kidneys fail and the pancreas becomes inflamed (pancreatitis). In stage 4 (after 5 days), the person either recovers or experiences failure of the liver and often other organs, which may be fatal.
If toxicity results from multiple smaller doses taken over time, the first indication of the problem may be abnormal liver function, sometimes with jaundice and/or bleeding.
If acetaminophen was taken within the previous several hours, activated charcoal may be given.
If the level of acetaminophen in the blood is high, acetylcysteine is generally given by mouth or by vein to reduce the toxicity of the acetaminophen. Acetylcysteine is given repeatedly, for one to several days. This antidote helps prevent liver injury but does not reverse injury that has already occurred. Therefore, acetylcysteine must be given before liver injury occurs. Treatment for liver failure or liver transplant may also be necessary.
If toxicity results from multiple smaller doses taken over time, acetylcysteine is given if tests indicate liver damage is possible and sometimes if liver damage has already developed.
Last full review/revision February 2013 by Gerald F. O'Malley, DO; Rika O'Malley, MD