After World War II, with the IG Farben conglomerate dismantled because of its central role in the Nazi regime, Sterling Products bought half of Bayer Ltd, the British Bayer subsidiary—the other half of which it already owned. However, Bayer Aspirin made up only a small fraction of the British aspirin market because of competition from Aspro, Disprin (a soluble aspirin drug) and other brands. Bayer Ltd began searching for new pain relievers to compete more effectively. After several moderately successful compound drugs that mainly utilized aspirin (Anadin and Excedrin), Bayer Ltds manager Laurie Spalton ordered an investigation of a substance that scientists at Yale had, in 1946, found to be the metabolically active derivative of acetanilide: acetaminophen. After clinical trials, Bayer Ltd brought acetaminophen to market as Panadol' in 1956.
However, Sterling Products did not market Panadol in the United States or other countries where Bayer Aspirin still dominated the aspirin market. Other firms began selling acetaminophen drugs, most significantly, McNeil Laboratories with liquid Tylenol in 1955, and Tylenol pills in 1958. By 1967, Tylenol was available without a prescription. Because it did not cause gastric irritation, acetaminophen rapidly displaced much of aspirins sales. Another analgesic, anti-inflammatory drug was introduced in 1962: ibuprofen (sold as Brufen in the U.K. and Motrin' in the U.S.). By the 1970s, aspirin had a relatively small portion of the pain reliever market, and in the 1980s sales decreased even more when ibuprofen became available without prescription.
Also in the early 1980s, several studies suggested a link between childrens consumption of aspirin and Reyes syndrome, a potentially fatal disease. By 1986, the U.S. Food and Drug Administration required warning labels on all aspirin, further suppressing sales. The makers of Tylenol also filed a lawsuit against Anacin aspirin maker American Home Products, claiming that the failure to add warning labels before 1986 had unfairly held back Tylenol sales, though this suit was eventually dismissed.