James Roth, a U.S. gastroenterologist, advocated paracetamol as a gastric-friendly alternative to aspirin, which can irritate the stomach when taken without food. Roth was also principal consultant to McNeil Laboratories. In 1953, McNeil Laboratories introduced Algoson, a preparation containing paracetamol together with sodium butabarbital, a sedative. In 1955, McNeil Laboratories introduced Tylenol Elixir for children, which contained paracetamol as its sole active ingredient. It was originally marketed mainly towards children, but soon came to dominate the North American pain-killer market. There are a number of different varieties of Tylenol available today including extra-strength (with 500 milligrams of paracetamol), children’s doses, longer-lasting, and sleep aiding (in combination with diphenhydramine). In 2005, Tylenol Ultra was introduced in Canada, with 500 mg of paracetamol and 65 mg of caffeine; caffeine has vasoconstricting effects, for which there is some disputed evidence for additional effectiveness. The patent on paracetamol has long expired, and the continued success of Tylenol brand preparations are largely due to marketing, the backing and reputation of Johnson & Johnson, and new patented delivery mechanisms such as quick-release and extended-release forms of the medication.
Info gleaned from Wikipedia