For the average healthy adult, the recommended maximum dose of acetaminophen over a 24 hour period is four grams (4000 mg) or eight extra-strength pills. (Each extra-strength pill contains 500 mg and each regular strength pill contains 325 mg.) A person who drinks more than two alcoholic beverages per day, however, should not take more than two grams of acetaminophen over 24 hours, as discussed below. For children, the dose is based on their weight and age, and explicit instructions are given in the package insert. If these guidelines for adults and children are followed, acetaminophen is safe and carries essentially no risk of liver injury.
On the other hand, a single dose of 7 to 10 grams of acetaminophen (14 to 20 extra-strength tablets) can cause liver injury in the average healthy adult. Note that this amount is about twice the recommended maximum dose for a 24 hour period. In children, a single dose of 140 mg/kg (body weight) of acetaminophen can result in liver injury. Amounts of acetaminophen, however, as low as 3 to 4 grams in a single dose or 4 to 6 grams over 24 hours have been reported to cause severe liver injury in some people, sometimes even resulting in death. It seems that certain individuals, for example, those who regularly drink alcohol, are more prone than others to developing acetaminophen-induced liver damage. To understand this increased susceptibility in some people, it is useful to know how acetaminophen is processed (metabolized) in the liver and how the drug causes liver injury.