Acetaminophen is the most commonly used drug ingredient in America. It is found in over 600 of the most commonly used over-the-counter (OTC) and prescription drugs, including Tylenol, Robitussin, Dayquil, Nyquil and so many more. An estimated 50 million Americans take acetaminophen every week. When taken as directed, acetaminophen is safe and effective. Taking too much acetaminophen, however, can cause severe liver damage.