ACETAMINOPHEN

Acetaminophen (also known as paracetamol) is the most widely used prescription and non-prescription painkiller worldwide. It is effective against such common pains as headaches, menstrual pain, and sunburn. First made in 1877, it is on the World Health Organization’s list of the most effective and safe medicines needed for a healthcare system.

CHEMICAL NAME

N-(4-hydroxyphenyl)acetamide, N-(4-hydroxyphenyl)ethanamide

MEDICINES

First used clinically in 1893, acetaminophen did not enter the U.S. market until 1950. Best known by the brand name Tylenol, it is also found in a wide variety of other medications.

HOW IT WORKS

Despite its long history and widespread use, the exact mechanisms behind acetaminophen’s effectiveness are still unclear. Scientists think it reduces the intensity of pain signals, possibly also preventing the release of substances that increase pain and body temperature. Caffeine is sometimes added to make it work faster.

SIDE EFFECTS

Acetaminophen is a major cause of acute liver failure in the U.S. and abroad. An estimated 50 million Americans use acetaminophen each week, so taking the right dose is critical. In the U.S., the makers of Tylenol have now lowered the maximum daily dose from eight 500 mg pills per day to six. Some experts have advised against taking acetaminophen combined with caffeine. But a meta-analysis by the Cochrane Collaboration, a UK nonprofit that compares clinical studies, found that when added to a standard analgesic such as acetaminophen or ibuprofen, the caffeine equivalent of a mug of coffee increased the number of people who reported good pain relief by up to 10%, as compared with the analgesic alone.

INTERACTIONS

Taking acetaminophen along with barbiturates (such as phenobarbital) or alcohol increases the risk of liver damage. Using antipsychotic medicines (such as clozapine) in combination with acetaminophen can lead to agranulocytosis, an acute infection associated with an extreme reduction of the white blood cells. Acetaminophen also interferes with some antibiotics (such as chloramphenicol).

PROPER USE

The maximum daily dose of acetaminophen depends on a person’s age and weight. Selfmedicating adults and adolescents weighing 130 pounds or more should not exceed six 500 mg pills per day (two every eight hours). Those weighing less than 130 pounds should take no more than 30 mg per pound per day.