Aspirin

Clinical dataPronunciationTrade namesBayer Aspirin, othersOther namesAHFS/Drugs.comMonographMedlinePlusa682878License dataPregnancy
categoryRoutes of
administrationOral, rectalDrug classNonsteroidal anti-inflammatory drug (NSAID)ATC codeLegal statusLegal statusPharmacokinetic dataBioavailability80–100%Protein binding80–90%MetabolismLiver (CYP2C19 and possibly CYP3A), some is also hydrolysed to salicylate in the gut wall.Elimination half-lifeDose-dependent; 2–3h for low doses (100mg or less), 15–30h for larger doses.ExcretionUrine (80–100%), sweat, saliva, fecesIdentifiersCAS NumberPubChemCIDIUPHAR/BPSDrugBankChemSpiderUNIIKEGGChEBIChEMBLPDB ligandCompTox Dashboard(EPA)ECHA InfoCard100.000.059Chemical and physical dataFormulaC₉H₈O₄Molar mass180.159 g·mol3D model (JSmol)Density1.40 g/cmMelting point135 °C (275 °F) Boiling point140 °C (284 °F) (decomposes)Solubility in water3g/L

Aspirin () is the genericized trademark for acetylsalicylic acid (ASA), a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and inflammation, and as an antithrombotic. Aspirin is used to treat inflammatory conditions including Kawasaki disease, pericarditis, and rheumatic fever.

Aspirin is also used long-term to reduce the chance of heart attack, ischaemic stroke, and blood clots occurring in people considered to be at high risk for such events. 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 viral 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), salicin, is metabolized in the human gut into the medicinally active compound salicylic acid and has been used for its health effects for at least 2,400 years. Pharmacology sought a synthetic alternative. In 1853, the 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, mostly of the German company Bayer, established the chemical structure and devised more efficient production methods. Felix Hoffmann (or perhaps Arthur Eichengrün) of Bayer was the first to produce acetylsalicylic acid in a pure, stable form in 1897. By 1899, Bayer had dubbed this drug Aspirin and was selling it globally.

Aspirin is available without medical prescription as a proprietary or generic medication in most jurisdictions. It is one of the most widely used medications globally, with an estimated 40,000 tonnes (44,000 tons) (50 to 120 billion pills) consumed each year, and is on the World Health Organization's List of Essential Medicines. In 2023, it was the 46th most commonly prescribed medication in the United States, with more than 14million prescriptions.