Study: High doses of painkiller produce abnormal liver tests

CHICAGO -- Healthy adults taking maximum doses of Tylenol for two weeks had abnormal liver test results in a small study, researchers found, raising concerns that even recommended amounts of the popular painkiller might lead to liver damage.

In the study, 106 participants took four grams of Tylenol -- equivalent to eight extra-strength Tylenol tablets -- each day for two weeks. Some took Tylenol alone and some took it with an opioid painkiller. Dummy pills were given to 39 others.

There were no alarming liver test results among the people who took the placebos. But nearly 40 percent of people in all the other groups had abnormal test results that would signal liver damage, according to the study that appears in today's Journal of the American Medical Association.

"I would urge the public not to exceed four grams a day. This is a drug that has a rather narrow safety window," said a study co-author, Dr. Neil Kaplowitz of the University of Southern California.

Heavy drinkers should take no more than two grams daily, Kaplowitz said.

Acetaminophen is more popular than aspirin or ibuprofen. Each week, one in five U.S. adults uses it for pain or fever, a 2002 survey found.

Acetaminophen is included in numerous over-the-counter and prescription medications, making overdose possible as people unwittingly combine drugs. Overdoses of acetaminophen are the leading cause of acute liver failure.

"A week doesn't go by when I don't have to talk to someone about how much they're taking," said Kathleen Besinque of the USC School of Pharmacy.

Watkins said people considering switching painkillers should know that others have their own side effects, such as internal bleeding and stomach irritation.

New research under way at the University of North Carolina may determine if acetaminophen's effect on the liver continues for long-term, high-dose users, or if the body adapts, Watkins said.

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