Aspirin — History, Pharmacology & Modern Evidence

Aspirin (acetylsalicylic acid, ASA) is one of the most widely used and most thoroughly studied medications in the history of medicine. Synthesized in pure, stable form by Bayer chemist Felix Hoffmann in 1897 and brought to market in 1899, aspirin has spent more than a century evolving from a simple analgesic and antipyretic into a cornerstone of modern cardiovascular prevention. Its mechanism — irreversible inhibition of cyclooxygenase (COX) enzymes — was not understood until Sir John Vane's 1971 discovery, which earned him the 1982 Nobel Prize in Physiology or Medicine.

Today aspirin sits at the intersection of pharmacology, cardiology, oncology, and nephrology. Low-dose aspirin (typically 81 mg in the United States, 75 mg in the United Kingdom) reduces recurrent heart attacks and ischemic strokes; chewing 162–325 mg of non-enteric aspirin during suspected acute myocardial infarction can be life-saving; and a growing body of evidence links long-term aspirin use to reduced incidence of colorectal cancer. Yet aspirin is not benign — gastrointestinal bleeding, hemorrhagic stroke, and renal injury are real risks that have driven major guideline shifts in primary prevention since 2018.

Sub-Articles

Aspirin Health Benefits

A comprehensive overview of aspirin's evidence-based benefits across cardiovascular protection, anti-inflammatory action, analgesia, antipyresis, colorectal cancer reduction, pre-eclampsia prevention, migraine relief, and emerging research in dementia and metabolic disease. Includes the modern dosing landscape and current USPSTF guidance on who should and should not take aspirin.

Aspirin for Heart Attack Prevention

The cardiovascular case for aspirin: the landmark ISIS-2 acute MI trial (1988), the Physicians' Health Study (1989), the Antithrombotic Trialists' Collaboration meta-analyses, and the 2018 trio (ARRIVE, ASCEND, ASPREE) that reshaped primary prevention guidance. Covers the chew-an-aspirin acute chest pain protocol, dual antiplatelet therapy after stents, aspirin resistance, and dosing forms.

Aspirin for Stroke Prevention

Aspirin's role in primary prevention, secondary prevention after stroke or TIA, and acute ischemic stroke treatment. Covers the IST and CAST 1997 trials, CHANCE and POINT dual antiplatelet trials, why aspirin is no longer adequate alone for atrial fibrillation, and the critical distinction between ischemic and hemorrhagic stroke risk.

Aspirin & The Kidneys

The renal-physiology side of NSAID use: prostaglandin-mediated afferent arteriole vasodilation, acute kidney injury, analgesic nephropathy and papillary necrosis, the classic "triple whammy" of NSAID + ACE inhibitor + diuretic, considerations in chronic kidney disease and dialysis patients, and whether low-dose 81 mg carries meaningful renal risk.

Aspirin & Cancer Prevention

The 30-year colorectal cancer story: observational evidence from the Nurses' Health Study, randomized trial follow-up by Rothwell and colleagues, the CAPP2 Lynch syndrome trial, and the ongoing Add-Aspirin adjuvant cancer trial. Honest framing of the USPSTF's 2016 recommendation and 2022 walk-back, plus emerging signals in esophageal, gastric, pancreatic, and other cancers.

Aspirin Side Effects, Risks & Contraindications

The full risk profile: gastrointestinal bleeding and peptic ulcer disease, hemorrhagic stroke, Reye's syndrome in children and adolescents, tinnitus and salicylate toxicity, aspirin-exacerbated respiratory disease (Samter's triad), drug interactions with anticoagulants and SSRIs, pregnancy considerations, and perioperative management.

A Brief History of Aspirin

Ancient Origins: Willow Bark

The medicinal use of willow bark (genus Salix) dates back at least 4,000 years. Sumerian clay tablets and the Egyptian Ebers Papyrus (c. 1534 BCE) describe its use for pain and inflammation. Hippocrates (c. 400 BCE) recommended chewing willow bark for fever and chewing willow leaves to relieve the pain of childbirth. The Roman encyclopedist Celsus and the Greek physician Dioscorides recorded similar uses, and willow remained a staple folk remedy throughout the medieval era.

1763: Reverend Edward Stone

The modern scientific story of aspirin begins on April 25, 1763, when an English clergyman, the Reverend Edward Stone, presented a paper to the Royal Society describing the use of dried, powdered willow bark to reduce the fevers of ague (malaria) in 50 patients. Stone had been guided by the now-discredited "doctrine of signatures" — he reasoned that because willow grew in damp places where ague thrived, it might contain a remedy for that condition. The doctrine was wrong, but the willow bark was right.

1828–1838: Isolation of Salicin and Salicylic Acid

In 1828, the German pharmacy professor Johann Andreas Buchner isolated a small quantity of bitter yellow crystals from willow bark and named them salicin (from the Latin salix, willow). The Italian chemist Raffaele Piria in 1838 hydrolyzed salicin to produce salicylic acid — the active anti-inflammatory metabolite. Salicylic acid was effective but extremely harsh on the stomach lining and intolerable in long-term use.

1897: Felix Hoffmann and Bayer

The decisive breakthrough came at the Bayer pharmaceutical laboratories in Elberfeld, Germany. On August 10, 1897, the chemist Felix Hoffmann recorded in his laboratory notebook the synthesis of a stable, pure form of acetylsalicylic acid — salicylic acid with an acetyl group attached, which dramatically reduced gastric irritation while preserving therapeutic activity. (Hoffmann's colleague Arthur Eichengrün, a Jewish chemist whose contributions Bayer subsequently minimized during the Nazi era, later disputed Hoffmann's primacy and claimed credit for both the project's direction and the clinical testing strategy.)

1899: The Aspirin Trademark

Bayer registered the trademark "Aspirin" on March 6, 1899. The name combined "a" (for acetyl), "spir" (for Spiraea, the meadowsweet plant from which salicylic acid had also been isolated), and "in" (a common pharmaceutical suffix). Aspirin was sold initially as a powder to physicians, then as the now-iconic tablet form beginning in 1900.

1918–1919: The Spanish Flu Pandemic

Aspirin played a complicated role in the 1918–1919 influenza pandemic. Doses recommended at the time were extraordinarily high by modern standards (up to 30 g/day in some cases), and a 2009 analysis published in Clinical Infectious Diseases argued that salicylate toxicity and pulmonary edema may have contributed to the high case-fatality rate among young adults. The Treaty of Versailles also stripped Bayer of its U.S. trademark rights to "aspirin," which became a generic term in the United States, United Kingdom, France, and several other countries.

1971: Sir John Vane Discovers the Mechanism

For 70 years aspirin worked without anyone knowing how. In 1971, the British pharmacologist Sir John Vane, then at the Royal College of Surgeons in London, published in Nature New Biology the discovery that aspirin acted by inhibiting the production of prostaglandins — lipid signaling molecules that mediate inflammation, pain, fever, and platelet aggregation. The enzyme target was later named cyclooxygenase (COX), and aspirin was found to inhibit it irreversibly by acetylating a serine residue in the active site — a unique mechanism among NSAIDs that explains why a single low dose silences platelet COX-1 for the platelet's entire 7–10 day lifespan. Vane shared the 1982 Nobel Prize in Physiology or Medicine with Bengt Samuelsson and Sune Bergström for this work.

1988: ISIS-2 and the Cardiovascular Era

The cardiovascular era of aspirin began definitively with the publication of the ISIS-2 trial in The Lancet in 1988. The trial randomized 17,187 patients with suspected acute myocardial infarction to streptokinase, aspirin (162.5 mg daily), both, or neither. Aspirin alone reduced 5-week vascular mortality by 23%; the combination of aspirin and streptokinase reduced it by 42%. The Antithrombotic Trialists' Collaboration meta-analyses of subsequent decades cemented aspirin's role in secondary cardiovascular prevention.

2010s: COX-2 Selectivity, Cancer Prevention, and the Primary-Prevention Reckoning

Two parallel research streams reshaped aspirin in the 2010s. First, long-term follow-up of cardiovascular trials by Peter Rothwell's group at Oxford documented that aspirin reduced the long-term incidence and mortality of colorectal cancer — a finding strengthened by the CAPP2 trial in patients with Lynch syndrome. Second, the 2018 trio of large primary-prevention trials — ARRIVE, ASCEND, and ASPREE — showed that for adults without established cardiovascular disease, the bleeding risk of daily aspirin was now nearly equal to its modest benefit, leading the U.S. Preventive Services Task Force in 2022 to substantially narrow its primary-prevention recommendation.

How Aspirin Works: A Quick Pharmacology Primer

Cyclooxygenase (COX) inhibition. Aspirin acetylates a serine residue (Ser-530 in COX-1; Ser-516 in COX-2) in the cyclooxygenase active site, blocking the conversion of arachidonic acid to prostaglandin H₂. This inhibition is irreversible — restoration of activity requires synthesis of new enzyme.
Platelet COX-1 silencing. Platelets cannot synthesize new protein. A single low dose of aspirin therefore blocks platelet thromboxane A₂ production for the platelet's full 7–10 day lifespan, even though aspirin's plasma half-life is only about 15–30 minutes.
Anti-inflammatory action. At higher doses (typically 1–4 g/day) aspirin inhibits COX-2 in inflamed tissues, reducing prostaglandin E₂ and prostacyclin. This is the analgesic and antipyretic dose range.
Aspirin-triggered lipoxins (ATLs). Acetylation of COX-2 does not simply silence the enzyme — it changes its catalytic activity to produce 15-R-HETE, which is converted by leukocyte 5-lipoxygenase to aspirin-triggered lipoxins, pro-resolving mediators that actively dampen inflammation.
Salicylate metabolites. Aspirin is rapidly hydrolyzed to salicylic acid, which is responsible for most of the systemic anti-inflammatory and antipyretic activity at higher doses.

Modern Dose Categories

Low-dose (75–100 mg/day): antiplatelet only; the cardiovascular prevention dose. Standard U.S. tablet is 81 mg ("baby aspirin"); standard U.K. tablet is 75 mg.
Analgesic dose (325–650 mg every 4–6 hours): pain, fever, headache.
Anti-inflammatory dose (2.4–4 g/day in divided doses): historically used for rheumatoid arthritis and acute rheumatic fever; largely supplanted by other NSAIDs and DMARDs but still used in Kawasaki disease.
Acute MI loading dose: chew 162–325 mg of non-enteric aspirin at first symptoms, while awaiting EMS. The non-enteric, chewed form is critical — it bypasses the slow dissolution of enteric coatings and achieves rapid platelet inhibition.

Key Research Papers & Resources

Vane JR. Inhibition of prostaglandin synthesis as a mechanism of action for aspirin-like drugs. Nature New Biology 1971;231(25):232–235. doi.org/10.1038/newbio231232a0
ISIS-2 Collaborative Group. Randomised trial of intravenous streptokinase, oral aspirin, both, or neither among 17,187 cases of suspected acute myocardial infarction: ISIS-2. Lancet 1988;2(8607):349–360. pubmed.ncbi.nlm.nih.gov/2899772
Steering Committee of the Physicians' Health Study Research Group. Final report on the aspirin component of the ongoing Physicians' Health Study. N Engl J Med 1989;321(3):129–135. nejm.org/doi/10.1056/NEJM198907203210301
Antithrombotic Trialists' Collaboration. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet 2009;373(9678):1849–1860. doi.org/10.1016/S0140-6736(09)60503-1
McNeil JJ, et al. Effect of aspirin on cardiovascular events and bleeding in the healthy elderly (ASPREE). N Engl J Med 2018;379(16):1509–1518. nejm.org/doi/10.1056/NEJMoa1805819
U.S. Preventive Services Task Force. Aspirin Use to Prevent Cardiovascular Disease: Recommendation Statement. JAMA 2022;327(16):1577–1584. jamanetwork.com/journals/jama/fullarticle/2791399
Rothwell PM, et al. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet 2010;376(9754):1741–1750. doi.org/10.1016/S0140-6736(10)61543-7
Burn J, et al. Cancer prevention with aspirin in hereditary colorectal cancer (Lynch syndrome), 10-year follow-up and registry-based 20-year data in the CAPP2 study. Lancet 2020;395(10240):1855–1863. doi.org/10.1016/S0140-6736(20)30366-4
Jeffreys D. Aspirin: The Remarkable Story of a Wonder Drug. Bloomsbury, 2004 — the standard popular history of aspirin and Bayer.