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Antiplatelet / NSAID / Antipyretic / Analgesic Pregnancy: First and second trimester: should not be given unless clearly necessary; if used, keep dose as low and duration as short as possible (from gestational week 20 onward may cause oligohydramnios/ductus arteriosus constriction - consider antenatal monitoring). Third trimester: contraindicated (see §4.3). Low doses up to and including 100 mg/day for restricted obstetrical use appear safe under specialised monitoring.

Aspirin

Brand names: Disprin, Nu-Seals, Micropirin

Used in: Stroke & TIA

Low-dose aspirin is an antiplatelet for secondary prevention of cardiovascular events and in acute coronary syndromes; higher doses are analgesic and antipyretic.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Analgesic/antipyretic/anti-inflammatory: 300-900 mg per dose. Antithrombotic (long-term following myocardial infarction, transient ischaemic attack, or unstable angina): 75-150 mg once daily.
Route: Oral
Frequency: Analgesic dose: repeated three to four times daily according to clinical needs. Antithrombotic dose: once daily.
Max: Analgesic: acute rheumatic disorders 4-8 g daily in divided doses. Antithrombotic: up to 300 mg a day in some circumstances (short term, on the advice of a doctor).
SPC covers two distinct indications. ANALGESIC/ANTIPYRETIC/ANTI-INFLAMMATORY dose is 300-900 mg three to four times daily; in acute rheumatic disorders 4-8 g daily in divided doses. ANTITHROMBOTIC (antiplatelet) dose is 75-150 mg once daily for long-term use after MI, TIA or in unstable angina, with up to 300 mg/day in some short-term circumstances on a doctor's advice. Elderly: as for adults but more likely to experience gastric side-effects and tinnitus. Patients should seek the advice of a doctor before commencing antithrombotic therapy for the first time.

Dose adjustments

Renal

Use with caution in patients with impaired renal function; avoid if severe.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Directions drink a full glass of water with each dose adults and children 12 years and over: take 4 to 8 tablets every 4 hours not to exceed 48 tablets in 24 hours unless directed by a doctor children under 12 years: consult a doctor

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-04-16. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Hypoprothrombinaemia, haemophilia, haemorrhagic disease or a history of bleeding disorders
  • Cerebral haemorrhage
  • Active peptic ulceration or a history of peptic ulceration
  • Third trimester of pregnancy
  • Women who are breastfeeding

Side effects

  • Gastrointestinal irritation, nausea, vomiting, dyspepsia, gastritis, gastrointestinal erosions/ulcer/bleeding (most common adverse events)
  • Hypersensitivity reactions including skin rashes, urticaria, angioedema, asthma, bronchospasm and anaphylaxis
  • Anaemia, bleeding disorders, thrombocytopenia
  • Tinnitus
  • Cerebral haemorrhage; haematoma, haemorrhage; epistaxis; prolonged bleeding time

Interactions

  • Metamizole may reduce the antiplatelet effect of acetylsalicylic acid (caution with low-dose aspirin for cardioprotection)
  • Salicylates may enhance the effect of oral hypoglycaemic agents, phenytoin and sodium valproate
  • Inhibit the uricosuric effect of probenecid and may increase the toxicity of sulphonamides
  • ACE inhibitors: aspirin at higher doses decreases glomerular filtration and antihypertensive effect
  • Diuretics: can increase the risk of nephrotoxicity of NSAIDs

Clinical monograph

How it works

It irreversibly inhibits platelet cyclo-oxygenase-1, reducing thromboxane-A2-mediated aggregation for the lifespan of the platelet.

Prescribing in practice

  • Gastrointestinal irritation and bleeding occur — consider gastroprotection in at-risk patients.
  • It can trigger bronchospasm in aspirin-sensitive asthma.
  • Avoid in children under 16 (Reye's syndrome) except for specific indications; bleeding risk rises with other antithrombotics.

Monitoring

Watch for gastrointestinal symptoms and bleeding.

Counselling the patient

  • Take it with or after food.
  • Report indigestion, black stools or unusual bleeding.
  • Do not give aspirin to children unless specifically told to.

Evidence & guidelines

Established for secondary cardiovascular prevention; routine primary prevention is no longer generally recommended.

Reference: NICE NG185 (ACS, 2020); NICE NG128 (Stroke, 2022); NICE NG17 (Headaches); ESC Guidelines on ACS (2023); ASCEND trial (NEJM 2018); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

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