Aspirin is an antiinflammatory compound that inhibits NFκB, cylooxygenase-1 (Cox-1), and cyclooxygenase-2 (Cox-2). NFκB is a transcription factor that plays an important role in the expression of cellular and viral genes, which regulate the inflammatory response and infection. Adhesion molecules IL-1 and IL-6 are genes regulated by NFκB. Along with sodium salicylate (sc-3520), aspirin has been shown to block the long terminal repeat from the human immunodeficiency virus and the Ig κ enhancer from NFκB dependent transcription. Research indicates that aspirin acts at a site downstream of glutamate receptors and blocks induction of NFκB mediated by glutamate. Additional studies suggest that aspirin and sodium salicylate specifically inhibit IKKβ, which results in the blocking of NFκB genes responsible for the inflammatory response. Aspirin has also been described to elevate extracellular adenosine levels, downregulate the expression and activity of inducible NOS, decrease the levels of adenosine triphosphate, act on multiple mitogen-activated protein kinase activities, and block the uncoupling of oxidative phosphorylation. Studies reveal that aspirin alters the equilibrium of Mcl-1/Noxa, giving rise to apoptosis of leukemia cells, independent of NFκB and MAPKs.

Aspirin is  used long-term to help prevent further heart attacks, ischaemic strokes, and blood clots in people at high risk.For pain or fever, effects typically begin within 30 minutes.Aspirin works similarly to other NSAIDs but also suppresses the normal functioning of platelets.

One common adverse effect is an upset stomach.More significant side effects include stomach ulcers, stomach bleeding, and worsening asthma.Bleeding risk is greater among those who are older, drink alcohol, take other NSAIDs, or are on other blood thinners.Aspirin is not recommended in the last part of pregnancy.It is not generally recommended in children with infections because of the risk of Reye syndrome.High doses may result in ringing in the ears.

A precursor to aspirin found in the bark of the willow tree (genus Salix) has been used for its health effects for at least 2,400 years. In 1853, chemist Charles Frédéric Gerhardt treated the medicine sodium salicylate with acetyl chloride to produce acetylsalicylic acid for the first time. Over the next 50 years, other chemists established the chemical structure and devised more efficient production methods.