Johnson & Johnson’s popular pain reliever Tylenol is found in many over-the-counter and prescription medications. And Tylenol overdose is the most common cause of acute liver failure in the country.

Tylenol (acetaminophen) is the most popular over-the-counter (OTC) pain relief medication used in the United States and around the world. According to the U.S. Food and Drug Administration (FDA), Americans bought 28 billion doses of products containing Tylenol in 2005 alone.

Manufactured by Johnson & Johnson subsidiary McNeil Laboratories, the drug is also available as a generic. It is marketed as an effective painkiller that is safer than non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin or ibuprofen, which are associated with stomach discomfort or bleeding. Pharmacies compound Tylenol into more than 600 prescription and OTC medicines, and the drug generates more than $1 billion a year for McNeil.

However, Tylenol is not without its serious complications. The active ingredient in Tylenol, acetaminophen, accounts for more than 100,000 calls to poison centers, roughly 60,000 emergency-room visits and hundreds of deaths each year in the United States. Acetaminophen poisoning is the most common forms of drug toxicity in the world, according to the National Institutes of Health (NIH).

How Does Tylenol Cause Liver Damage?

Because Tylenol is available over-the-counter, a common misconception is that it is not dangerous. For some people, even going slightly over the recommended amount can cause acute liver failure, a condition that can have deadly consequences.

Liver damage is the most serious side effect of Tylenol and can be fatal. Overdosing on Tylenol or other acetaminophen-containing drugs leads to Tylenol poisoning, which in turn leads to liver damage and/or failure. After someone takes Tylenol, the drug is primarily metabolized in the liver. Under normal conditions, the liver eliminates acetaminophen and its byproducts.

When too much acetaminophen builds up in the liver, the pathways to eliminate these compounds can overload. When this happens, the body uses another pathway in the liver, called the cytochrome P-450 system, to remove these byproducts. P-450 processes these byproducts but creates a toxic compound called NAPQI.

Symptoms of Tylenol Overdose

Tylenol overdose is more common than many might think, and anyone who takes Tylenol because of chronic pain has the greatest risk of accidental overdose. The early symptoms of liver damage are often vague and include loss of appetite, nausea, and vomiting, and can initially mistaken for other ailments, like the flu. More serious symptoms include abdominal pain, convulsions, diarrhea, irritability, and coma.

Other signs of liver damage may include:

• Dark colored urine
• Clay colored stools
• Yellowing of the skin or eyes (jaundice)

FDA Warns Tylenol Can Cause Liver Damage

In 2009, the FDA issued guidelines for adding overdose guidelines to Tylenol packages and in 2011 the agency confirmed the link between Tylenol and liver damage.

In October 2013, Johnson & Johnson added a warning to the caps of bottles of Extra Strength Tylenol warning consumers that the drug contains acetaminophen and may cause liver failure. Severe liver damage from the drug led people to file Tylenol lawsuits against Johnson & Johnson and/or McNeil.

On April 1, 2013, a judge consolidated several federal Tylenol lawsuits in multidistrict litigation (MDL) in the U.S. District Court for the Eastern District of Pennsylvania.