Health regulators in the U.S. announced Thursday they are limiting the amount of acetaminophen found in prescription painkillers, in an effort to cut the thousands of cases of liver damage in the United States each year.

The Food and Drug Administration says it will cap the amount of acetaminophen in the drugs at 325 milligrams per capsule.

It will also require a Boxed Warning on all prescription medications containing acetaminophen to highlight the potential risk for severe liver injury.

Boxed Warnings are FDA's strongest warnings for prescription drug products, used for calling attention to serious or life-threatening risks

As well, it will require a warning on the labels of prescription medicaions with acetaminophen to highlight the potential for allergic reactions from acetaminophen, such as swelling of the face, mouth, and throat, itching, and rash.

Regulators say acetaminophen is dangerous at the larger doses found in prescription combination drugs.

Over-the-counter pain and fever medications that contain acetaminophen, such as Tylenol, are already required in the U.S. to include information in their labeling about the potential for safety risks, including liver injury.

The FDA says that acetaminophen is the leading cause of liver failure in the United States. The condition sends 56,000 people to the emergency room annually, and leads to the deaths of about 200 Americans die each year. About 120 of those deaths are linked to prescription drugs with acetaminophen, the FDA estimates.

Health Canada, meanwhile, says it's aware of the changes announced Thursday by the FDA.

It says that in September 2009, it finalized a new labelling standard for non-prescription products containing acetaminophen. This labelling standard warns of potential serious and possibly fatal liver damage in the event of an overdose.

"Health Canada continues to review emerging and available safety evidence, including that used by the FDA to reach its decision and will determine if any new action may be needed to protect health and safety," the agency said in a statement.

The agency then offered these tips for taking medications safely:

  • Always read the product label and follow the instructions.
  • Be careful when taking multiple products at once. For example, acetaminophen is contained in some pain relievers as well as decongestants and cough and cold remedies. In such cases, be careful to avoid exceeding the maximum recommended daily dosage of acetaminophen from the combined sources by considering product labelling and medication instructions.
  • With prescription products, talk to your doctor, pharmacist or other health care professional and follow their instructions.
  • Know when to take medication, how often, and for how long.