These compounds include Excedrin, Midol Teen Formula, Theraflu, Alka-Seltzer Plus Cold Medicine, and NyQuil Cold and Flu, as well as other over-the-counter drugs and many prescription narcotics, like Vicodin and Percocet.

The authors of the study, which is appearing in the December issue of Hepatology, say the combination of acetaminophen's quiet ubiquity in over-the-counter remedies and its pairing with narcotics in potentially addictive drugs like Vicodin and Percocet can make it too easy for some patients to swallow much more than the maximum recommended dose inadvertently.

"It's extremely frustrating to see people come into the hospital who felt fine several days ago, but now need a new liver," said Dr. Tim Davern, one of the authors and a gastroenterologist with the liver transplant program of the University of California at San Francisco. "Most had no idea that what they were taking could have that sort of effect." The numbers of poisonings, however, are still tiny in comparison with the millions of people who use over-the-counter and prescription drugs with acetaminophen.

Dr. Davern and a team of colleagues from other centers led by Dr. Anne Larson at the University of Washington Medical Center in Seattle, tracked the 662 consecutive patients who showed up with acute liver failure at 23 transplant centers across the United States from 1998 to 2003.

Acetaminophen poisoning was to blame in nearly half the patients, the scientists found. The proportion of cases linked to the drug rose to 51 percent in 2003 from 28 percent in 1998. Not all the poisonings were accidental. An estimated 44 percent were suicide attempts by people who swallowed fistfuls of pills. "It's a grisly way to die," Dr. Davern said, adding that patients who survive sometimes suffer profound brain damage.