acetaminophen

acetaminophen, drug used in the treatment of mild to moderate pain, such as headache and pain in joints and muscles, and to reduce fever. The drug is marketed under several trade names, including Tylenol, Tempra, and Panadol, and outside the United States it is known as paracetamol.

Mechanism of action

Acetaminophen is the major metabolite of acetanilide and phenacetin, which were once commonly used drugs, and it is responsible for their analgesic (pain-relieving) effects. The exact mechanism by which acetaminophen exerts its actions, however, is not fully known. Initially, it was thought that the drug acts primarily by inhibiting cyclooxygenase (COX) enzymes in the central nervous system. This results in localized suppression of the synthesis of prostaglandins, which are key mediators of inflammation. However, additional research has shown that acetaminophen is a weak COX inhibitor, and alternative pathways that potentially explain its effects have been identified. Acetaminophen or its metabolite AM404, for example, appears to activate the endocannabinoid system, which is involved in the modulation of pain signaling, among other functions. The drug may also act on neurotransmitter systems, particularly those involving serotonin.

Uses

Acetaminophen is a popular over-the-counter medication that is commonly used to treat mild to moderate pain from various conditions, including headaches, dental pain, muscle aches, and menstrual cramps, as well as the discomfort associated with colds and sore throats. It is also effective in treating fever from various causes, including infections and vaccinations. In some cases, acetaminophen is combined with other medications, such as opioids, to treat more severe pain. A distinguishing feature of acetaminophen is that, unlike traditional nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, it does not exert significant anti-inflammatory effects.

Discover how ordinary objects work, and expand your understanding of the familiar.

SIGN UP

" height="20" alt="HEW Logo">

Thank you for signing up!"

Back to homepage

By clicking "Sign Up", you consent to the Britannica Privacy Policy and Terms of Use.

Side effects

Acetaminophen rarely triggers side effects, and in most cases when side effects occur, they are mild, involving symptoms such as nausea and mild stomach cramps or abdominal pain. Indeed, relative to aspirin, acetaminophen is much less likely to cause gastrointestinal side effects. However, prolonged or heavy use can be dangerous, and overdoses of acetaminophen can cause fatal liver damage. The risk of liver toxicity from acetaminophen is heightened by alcohol consumption, malnutrition, and preexisting liver disease.

Acetaminophen has also been implicated as a hormone disruptor, with prenatal exposure to the drug possibly correlated to the development of neurological disorders in children; no causal association has been established, however. Research has also linked acetaminophen use to alterations in risk perception and decision-making as well as increased risk-taking behavior.