johnson & johnson says starting in october, the caps of extra strength tylenol will have the message in big red print, contains acetaminophen and always read the label. >> extra strength tylenol tablet and acetaminophen pill is 500 milligrams. you could take eight of those every day. spaced out properly and you would still be within the safe range. >> reporter: the pain relieving ingredient is the nation's leading cause of sudden liver failure. as 33-year-old riley mcdermott learned firsthand it isn't just found in tylenol. >> if my fiance had gotten me to the e.r., a half an hour later, i would be dead. >> reporter: after inadvertently overdosing on a prescription codeine for an ankle injury and medicine to help her sleep she ended up on a liver transplant list. >> you are in pain. and you take something. you don't think of it building up in your body. >> liver damage is extremely rare. the more common problem is people overdosing on the drug which sends as many as 80,000 people in the u.s. to the e.r. each year.