CHICAGO (AP) — 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, he said.
Another co-author, Dr. Paul Watkins of the University of North Carolina, said he’s less worried than Dr. Kaplowitz, noting that acetaminophen, the active ingredient in Tylenol, has been used for 50 years and has a good safety record.
The maker of Tylenol, McNeil Consumer & Specialty Pharmaceuticals, said its own research found much lower rates of abnormal liver results. The company’s studies tracked high-dose users over longer periods than did the new study.
“It doesn’t lead to liver disease, and it usually resolves as patients continue to take acetaminophen,” said Dr. Edwin Kuffner, senior director of medical affairs at McNeil.
The researchers had been hired by the drug company Purdue Pharma LP, maker of the prescription painkiller OxyContin, to find out why abnormal liver tests were showing up in people testing a combination drug containing acetaminophen and the opiate hydrocodone.
Purdue Pharma stopped its hydrocodone study early because of the abnormal liver tests. Drs. Watkins and Kaplowitz thought they would find the culprit in hydrocodone’s interaction with acetaminophen.
“Our jaws dropped when we got the data,” Dr. Watkins said. “It doesn’t have anything to do with the opiate. It’s good ol’, garden-variety acetaminophen.”