Aspirin — Benefits Deep Dive

Aspirin (acetylsalicylic acid) was first made in its modern form in 1897 and introduced to the pharmaceutical market in 1899 (Kohl 1999); a 2019 history review describes it as the most widely used drug worldwide (Montinari 2019). Low-dose aspirin irreversibly acetylates a serine residue (Ser-529) of the cyclooxygenase-1 (COX-1) enzyme in platelets, and because platelets have limited capacity to make new protein and live 7-10 days in humans, the effect on thromboxane A2 lasts far longer than the drug itself (Patrono 2026). The same review links this platelet effect both to the prevention of atherothrombosis and to the increased risk of bleeding, and discusses a platelet-based explanation for aspirin's association with lower colorectal cancer risk. Four deep-dive pages below cover secondary versus primary cardiovascular prevention, the colorectal cancer findings, bleeding risk, and how low doses (75-100 mg) compare with higher doses (325 mg).

Deep-Dive Articles

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Cardiovascular Prevention

Irreversible COX-1 acetylation in platelets; in high-risk patients, antiplatelet therapy reduced serious vascular events by about one quarter in the 2002 Antithrombotic Trialists' meta-analysis; the 2018 primary-prevention trials (ARRIVE, ASCEND, ASPREE); and the 2022 USPSTF statement, which recommends against starting aspirin for primary prevention at 60 or older and calls the decision an individual one, with a small net benefit, for adults 40-59 with a 10% or greater 10-year risk.

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Colorectal Cancer Risk

In 20-year follow-up of four randomised trials of aspirin versus control, aspirin reduced colon cancer incidence (hazard ratio 0.76) and mortality (0.65), but not rectal cancer overall (Rothwell 2010). The mechanism is still debated (COX-2 in the colon or platelets), the CAPP2 trial in Lynch syndrome carriers found fewer colorectal cancers on 600 mg aspirin at 10 years, and in pooled trials the reduction in cancer deaths appeared only after about 5 years, later still for colorectal cancer (Rothwell 2011), while bleeding risk rises with age.

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Bleeding Risks and Cautions

The main harm of low-dose aspirin. Measured rates (major gastrointestinal bleeding up by about 0.12% per year in a meta-analysis of 22 trials; hemorrhagic stroke 0.04% vs 0.03% per year in primary-prevention trials), risk factors by age and history, the H. pylori and proton pump inhibitor trials, other NSAIDs and ibuprofen interference, the POISE-2 perioperative trial, label warnings, and Reye's syndrome.

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Low Dose vs Full Dose

How low doses compare with higher ones. In the ADAPTABLE trial (15,076 patients with cardiovascular disease, 2021), 81 mg and 325 mg daily did not differ significantly in cardiovascular events or major bleeding. Also covered: the 2002 meta-analysis finding that 75-150 mg daily was at least as effective as higher doses, and studies of enteric-coated versus plain aspirin.

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Table of Contents

  1. Deep-Dive Articles
  2. Why One Mechanism Produces So Many Effects
  3. Research Papers: Cardiovascular Prevention
  4. Research Papers: Colorectal Cancer
  5. Research Papers: Bleeding Risks
  6. Research Papers: Dosing & Pharmacology
  7. Research Papers: Cross-Cutting (Mechanism, History, Safety)
  8. External Authoritative Resources
  9. Connections
  10. Featured Videos

Why One Mechanism Produces So Many Effects

Willow bark was used as a painkiller and fever remedy by the Sumerians and Egyptians more than 3,500 years ago, and salicylates were extracted and synthesized by many researchers in the 19th century (Montinari 2019, PubMed PMID: 30391545). Acetylsalicylic acid was synthesized by Charles Gerhardt in 1853 and, in August 1897, by Felix Hoffmann, a chemist at a German drug company; it reached the pharmaceutical market in 1899 (Norn 2009, PubMed PMID: 20509453; Kohl 1999, PubMed PMID: 12799922). How it works was explained only decades later.

In 1971, John Vane, then working at the Royal College of Surgeons of England in London, showed that aspirin works by inhibiting the formation of prostaglandins; he shared the 1982 Nobel Prize in Physiology or Medicine with Sune Bergström and Bengt Samuelsson “for their discoveries concerning prostaglandins and related biologically active substances” (NobelPrize.org). The enzymes involved, COX-1 and COX-2, convert arachidonic acid to prostaglandin G2 and then H2, which is converted into prostacyclin, prostaglandin E2, thromboxane A2 and other prostanoids (Patrono 2026, PubMed PMID: 41592353). In 1975 Roth, Stanford and Majerus showed that aspirin acetylates the enzyme, acting as an active-site acetylating agent (Roth 1975, PubMed PMID: 810797); the acetylated residues are serine-529 in COX-1 and serine-516 in COX-2 (Tacconelli 2020, PubMed PMID: 32535107). The 2026 review notes that other NSAIDs such as ibuprofen and diclofenac do not achieve the same persistent platelet COX-1 inhibition.

The irreversibility matters most in platelets. Anucleate platelets have limited capacity to make new protein and live 7-10 days in humans, with only about 10-12% of circulating platelets newly formed each day; aspirin itself has a half-life of about 20 minutes. Once-daily low-dose aspirin (30-100 mg) suppresses platelet COX-1 activity by more than 97% throughout the dosing interval while leaving other COX-2-dependent sources of prostanoids, such as the blood vessel wall, largely unaffected; nucleated cells can make new enzyme within 4-6 hours (Patrono 2026). In 24 healthy volunteers taking 100 mg enteric-coated aspirin daily, serum thromboxane B2 was suppressed by about 99%, with about 76% of platelet COX-1 acetylated (Patrignani 2014, PubMed PMID: 24942808).

  1. Cardiovascular benefit — reduced thromboxane-A2-dependent platelet activation is linked to the prevention of atherothrombosis (Patrono 2026). See Cardiovascular Prevention.
  2. Colorectal cancer — whether low-dose aspirin lowers colorectal cancer risk by affecting COX-2 activity in colorectal adenomas is still debated (Tacconelli 2020); the 2026 review sets out a platelet-based explanation, in which activated platelets drive COX-2 induction and prostaglandin E2 release in the tumour environment (Patrono 2026). See Colorectal Cancer Risk.
  3. Anti-inflammatory and analgesic effect — the 2026 review gives analgesic/anti-inflammatory regimens as 325-650 mg three to four times daily, and notes that acetylating COX-2 requires repeated higher doses (650 mg four to six times daily) because nucleated cells resynthesize the enzyme within 4-6 hours (Patrono 2026).
  4. Anti-pyretic effect — in fever, neurons of the brain's preoptic area produce prostaglandin E2, which acts on PGE2 receptors to raise body temperature; a 2023 review lists aspirin among the classical antipyretic drugs (Santacroce 2023, PubMed PMID: 36984901).
  5. The downside: GI mucosal injury and bleeding — the 2026 review describes two COX-1-dependent mechanisms for upper gastrointestinal bleeding: inhibition of thromboxane-A2-mediated platelet function and impaired prostaglandin-E2-mediated protection of the stomach lining (Patrono 2026). See Bleeding Risks and Cautions.

The same review describes how these effects depend on dose differently: the platelet effect is dose-independent above about 30 mg daily, while the effect on the stomach lining rises with dose up to analgesic/anti-inflammatory regimens, and inhibited platelet function is largely responsible for the roughly 2-fold rise in upper gastrointestinal bleeding at 75-100 mg daily (Patrono 2026). In the McQuaid and Laine meta-analysis of 22 trials, the bleeding increase did not differ between 75-162.5 mg and >162.5-325 mg daily (PubMed PMID: 16887404), and in ADAPTABLE, 81 mg and 325 mg did not differ significantly in cardiovascular events or major bleeding (PubMed PMID: 33999548). The deep-dive on Low Dose vs Full Dose covers the dose comparisons in more detail.

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Research Papers: Cardiovascular Prevention

  1. Antithrombotic Trialists' Collaboration, BMJ 2002: collaborative meta-analysis of randomised trials of antiplatelet therapy in high-risk patients (287 studies; 135,000 patients in comparisons with control). — PubMed PMID: 11786451 (editorial note: previously described as 195 trials.)
  2. Antithrombotic Trialists' (ATT) Collaboration, Lancet 2009: aspirin in the primary and secondary prevention of vascular disease, individual participant data meta-analysis. — PubMed PMID: 19482214
  3. ISIS-2 trial (Second International Study of Infarct Survival): aspirin in acute MI. — PubMed PMID: 2899772
  4. ARRIVE trial: aspirin primary prevention in moderate-risk adults. — PubMed PMID: 30158069
  5. ASCEND trial: aspirin for primary prevention in diabetes. — PubMed PMID: 30146931
  6. ASPREE trial: aspirin in healthy older adults. — PubMed PMID: 30221597
  7. USPSTF 2022 recommendation on aspirin for primary CV prevention. — PubMed PMID: 35471505
  8. Physicians' Health Study (1989 NEJM): aspirin primary prevention foundation trial. — PubMed PMID: 2664509
  9. CAPRIE trial: clopidogrel vs aspirin in atherothrombotic events. — PubMed PMID: 8918275
  10. CURE trial: aspirin plus clopidogrel in acute coronary syndromes. — PubMed PMID: 11519503
  11. Women's Health Study: aspirin primary prevention in women (NEJM 2005) — PubMed PMID: 15753114

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Research Papers: Colorectal Cancer

  1. Rothwell PM et al., Lancet 2010: long-term aspirin and colorectal cancer incidence/mortality. — PubMed PMID: 20970847
  2. Rothwell PM et al., Lancet 2011: effect of daily aspirin on 20-year cancer mortality (pooled analysis) — PubMed PMID: 21144578
  3. Burn J et al., Lancet 2011: CAPP2 trial, long-term effect of aspirin on cancer risk in carriers of hereditary colorectal cancer (Lynch syndrome). — PubMed PMID: 22036019
  4. CAPP2 10-year follow-up confirming Lynch syndrome benefit. — PubMed PMID: 32534647
  5. Chan AT et al., JAMA 2005: long-term use of aspirin and NSAIDs and risk of colorectal cancer (Nurses' Health Study) — PubMed PMID: 16118381
  6. Cole BF et al., J Natl Cancer Inst 2009: aspirin for the chemoprevention of colorectal adenomas, meta-analysis of the randomized trials. — PubMed PMID: 19211452 (editorial note: previously listed as NEJM 2003; Cole is second author of the 2003 NEJM trial listed next.)
  7. Baron JA et al., NEJM 2003: a randomized trial of aspirin to prevent colorectal adenomas. — PubMed PMID: 12621133
  8. Cuzick J et al., Annals of Oncology 2015: estimates of benefits and harms of prophylactic use of aspirin in the general population. — PubMed PMID: 25096604
  9. Chan AT et al., JAMA 2009: aspirin use and survival after colorectal cancer diagnosis. — PubMed PMID: 19671906
  10. Drew DA et al., Nature Reviews Cancer 2016: aspirin and colorectal cancer, the promise of precision chemoprevention. — PubMed PMID: 26868177

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Research Papers: Bleeding Risks

  1. McQuaid KR & Laine L, Am J Med 2006: systematic review and meta-analysis of adverse events of low-dose aspirin and clopidogrel in randomized controlled trials. — PubMed PMID: 16887404
  2. Mahady SE et al., Gut 2021: major GI bleeding in older persons using aspirin, incidence and risk factors in the ASPREE randomised controlled trial. — PubMed PMID: 32747412 (editorial note: previously listed as an NEJM 2018 paper.)
  3. Bhatt DL et al., COGENT trial: PPI co-therapy with aspirin + clopidogrel. — PubMed PMID: 20925534
  4. García Rodríguez LA et al., Circulation 2011: risk of upper gastrointestinal bleeding with low-dose aspirin alone and in combination with clopidogrel and other medications. — PubMed PMID: 21357821 (editorial note: previously listed as BMJ 2011.)
  5. Hawkey CJ et al., Aliment Pharmacol Ther 2008: H. pylori eradication and aspirin GI risk. — Search PubMed (editorial note: the 2008 Hawkey trial in this journal compares lumiracoxib with traditional NSAIDs and is not an H. pylori study; the H. pylori trials are listed on the Bleeding Risks and Cautions page.)
  6. Catella-Lawson F et al., NEJM 2001: cyclooxygenase inhibitors and the antiplatelet effects of aspirin. — PubMed PMID: 11752357
  7. Sostres C & Gargallo CJ, Best Pract Res Clin Gastroenterol 2012: gastrointestinal lesions and complications of low-dose aspirin in the gastrointestinal tract. — PubMed PMID: 22542152 (editorial note: the second author was previously given as Lanas A.)
  8. Bibbins-Domingo K, USPSTF, Ann Intern Med 2016 (superseded by the 2022 statement): aspirin use for the primary prevention of cardiovascular disease and colorectal cancer. — PubMed PMID: 27064677

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Research Papers: Dosing & Pharmacology

  1. Jones WS et al., NEJM 2021: ADAPTABLE, comparative effectiveness of aspirin dosing (81 mg vs 325 mg) in cardiovascular disease. — PubMed PMID: 33999548
  2. Patrono C et al., NEJM 2005: low-dose aspirin for the prevention of atherothrombosis. — PubMed PMID: 16319386
  3. Roth GJ & Majerus PW, J Clin Invest 1975: the mechanism of the effect of aspirin on human platelets, I. acetylation of a particulate fraction protein. — PubMed PMID: 1159076
  4. Roth GJ, Stanford N & Majerus PW, Proc Natl Acad Sci U S A 1975: acetylation of prostaglandin synthase by aspirin. — PubMed PMID: 810797
  5. Vane JR, Nat New Biol 1971: aspirin inhibits prostaglandin synthesis (Nobel work) — PubMed PMID: 5284360
  6. Cox D et al., Stroke 2006: effect of enteric coating on antiplatelet activity of low-dose aspirin in healthy volunteers. — PubMed PMID: 16794200
  7. Eikelboom JW et al., Circulation 2002: aspirin-resistant thromboxane biosynthesis and the risk of myocardial infarction, stroke, or cardiovascular death in high-risk patients. — PubMed PMID: 11940542
  8. Maree AO et al., JACC 2005: platelet response to low-dose enteric-coated aspirin in patients with stable cardiovascular disease. — PubMed PMID: 16198840
  9. Newby LK et al., AHA scientific statement 2008: aspirin dose and CV prevention. — Search PubMed (editorial note: no 2008 AHA statement by Newby on aspirin dose was found in PubMed.)
  10. Rothwell PM et al., Lancet 2018: aspirin body-weight-dose effect on CV events. — PubMed PMID: 30017552
  11. Patrono C, NEJM 1994: aspirin as an antiplatelet drug. — PubMed PMID: 8145785
  12. Patrignani P et al., J Thromb Haemost 2014: reappraisal of the clinical pharmacology of low-dose aspirin by comparing novel direct and traditional indirect biomarkers of drug action. — PubMed PMID: 24942808
  13. Tacconelli S et al., Biochem Pharmacol 2020: characterization of cyclooxygenase-2 acetylation and prostanoid inhibition by aspirin in cellular systems. — PubMed PMID: 32535107

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Research Papers: Cross-Cutting (Mechanism, History, Safety)

  1. Mahmud SM et al., JNCI 2010: aspirin and prostate cancer mortality. — Search PubMed (editorial note: no 2010 JNCI paper by Mahmud on aspirin and prostate cancer mortality was found in PubMed; Mahmud's 2010 meta-analysis of NSAIDs and prostate cancer risk appeared in Int J Cancer, PMID 20091856.)
  2. Algra AM & Rothwell PM, Lancet Oncol 2012: aspirin and cancer incidence/metastasis. — PubMed PMID: 22440112
  3. Belay ED et al., NEJM 1999: Reye's syndrome in the United States from 1981 through 1997. — PubMed PMID: 10228187
  4. McNeil JJ et al., NEJM 2018: effect of aspirin on all-cause mortality in the healthy elderly (ASPREE). — PubMed PMID: 30221595 (editorial note: the link previously pointed to the companion ASPREE paper on disability-free survival.)
  5. Arnett DK et al., JACC 2019: 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease. — PubMed PMID: 30894318 (editorial note: the first author was previously given as Wilson PWF.)
  6. Berger JS et al., JAMA 2006: aspirin for the primary prevention of cardiovascular events in women and men, a sex-specific meta-analysis of randomized controlled trials. — PubMed PMID: 16418466
  7. Newburger JW et al., Circulation 2004: diagnosis, treatment, and long-term management of Kawasaki disease, AHA statement for health professionals — PubMed PMID: 15505111
  8. Landolfi R et al., NEJM 2004: efficacy and safety of low-dose aspirin (100 mg daily) in polycythemia vera (ECLAP trial) — PubMed PMID: 14711910
  9. Sneader W, BMJ 2000: the discovery of aspirin, a reappraisal — PubMed PMID: 11124191
  10. Montinari MR et al., Vascul Pharmacol 2019: the first 3500 years of aspirin history from its roots, a concise summary. — PubMed PMID: 30391545
  11. Norn S et al., Dan Medicinhist Arbog 2009: from willow bark to acetylsalicylic acid (in Danish, English abstract). — PubMed PMID: 20509453
  12. Kohl F, Schmerz 1999: a historical vignette on the introduction of acetylsalicylic acid to the market in 1899 (in German, English abstract). — PubMed PMID: 12799922
  13. Patrono C et al., Pharmacol Rev 2026: platelet activation, aspirin, and cancer, from basic science to clinical trials. — PubMed PMID: 41592353
  14. Santacroce L et al., Metabolites 2023: microbial and host metabolites at the backstage of fever (review). — PubMed PMID: 36984901
  15. Jeffreys D, "Aspirin: the remarkable story of a wonder drug" PubMed: aspirin history

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External Authoritative Resources

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Connections

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