Aspirin
Brand names: Disprin, Nu-Seals, Micropirin
Low-dose aspirin is an antiplatelet for secondary prevention of cardiovascular events and in acute coronary syndromes; higher doses are analgesic and antipyretic.
Adult dose
Dose adjustments
No numeric adjustment is given; severe impairment is a contraindication. SPC 4.3 lists 'Severe renal impairment' as a contraindication. 4.4: 'Acetylsalicylic acid should be used with caution in patients with moderately impaired renal or hepatic function (contraindicated if severe), or in patients who are dehydrated since the use of NSAIDs may result in deterioration of renal function.' 4.2 (elderly): 'The usual adult dose is recommended in the absence of severe renal or hepatic insufficiency.'
No numeric adjustment is given; severe impairment is a contraindication. SPC 4.3 lists 'Severe hepatic impairment' as a contraindication. 4.4: use with caution in moderately impaired hepatic function and 'Liver function tests should be performed regularly in patients presenting slight or moderate hepatic insufficiency.'
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 UKDirections 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
- Previous hypersensitivity reactions (e.g. asthma, rhinitis, angioedema or urticaria) to salicylates/aspirin or other substances with a similar mechanism of action, especially NSAIDs; and a history of asthma caused by salicylates or NSAIDs (4.3)
- Acute gastrointestinal ulcers (4.3)
- A history of gastrointestinal bleeding or perforation (gastric or intestinal failure) caused by previous NSAID therapy (4.3)
- Active or a history of recurrent gastric and duodenal ulcer/haemorrhage with episodes of proven ulceration or bleeding, or other kinds of bleeding such as cerebrovascular haemorrhages (4.3)
- Haemorrhagic diathesis; coagulation disorders such as haemophilia and thrombocytopenia (4.3)
- Severe hepatic impairment (4.3)
- Severe renal impairment (4.3)
- Severe cardiac insufficiency (4.3)
- Doses greater than 100 mg/day during the third trimester of pregnancy (4.3, 4.6)
- Methotrexate used at doses greater than 15 mg/week (4.3)
Side effects
- Blood - common: increased bleeding tendencies. Uncommon: thrombocytopenia, agranulocytosis, aplastic anaemia. Not known: bleeding with prolonged bleeding time such as epistaxis and gingival bleeding ('Symptoms may persist for a period of 4-8 days after acetylsalicylic acid discontinuation'); overt (haematemesis, melaena) or occult gastrointestinal bleeding, which may lead to iron deficiency anaemia (more common at higher doses) (4.8)
- Immune - uncommon: hypersensitivity reactions, angio-oedema, allergic oedema, anaphylactic reactions including shock (4.8)
- Metabolism - not known: hyperuricaemia, hypoglycaemia (4.8)
- Nervous system - uncommon: intracranial haemorrhage. Not known: headache, vertigo (4.8)
- Ear - not known: reduced hearing ability, tinnitus (4.8)
- Vascular - not known: haemorrhagic vasculitis (4.8)
- Respiratory - uncommon: rhinitis, dyspnoea. Rare: bronchospasm, asthma attacks (4.8)
- Gastrointestinal - common: dyspepsia, nausea, vomiting, diarrhoea. Rare: severe gastrointestinal haemorrhage, gastric or duodenal ulcers and perforation (4.8)
- Hepatobiliary - rare: Reye's syndrome. Not known: hepatic insufficiency, increased hepatic enzymes (4.8)
- Skin - uncommon: urticaria. Rare/not known: Stevens-Johnson syndrome, Lyell's syndrome, purpura, erythema nodosum, erythema multiforme - 4.4 requires that 'The treatment with Aspirin should be discontinued at the first appearance of skin rash, mucosal lesions, or any other sign of hypersensitivity' (4.4, 4.8)
- Renal - not known: impaired renal function, acute renal failure (4.8)
- Reproductive - not known: menorrhagia; 4.4 adds 'Aspirin is not recommended during menorrhagia where it may increase menstrual bleeding' (4.4, 4.8)
Monitoring
- Bleeding - 4.4: 'Patients should report any unusual bleeding symptoms to their physician. If gastrointestinal bleeding or ulceration occurs the treatment should be withdrawn.'
- Liver function tests regularly in patients with slight or moderate hepatic insufficiency (4.4)
- Renal function - use with caution in moderate impairment and in dehydrated patients 'since the use of NSAIDs may result in deterioration of renal function' (4.4)
- Regular review of elderly patients where prolonged therapy is required (4.4)
- Skin and mucosa - discontinue at the first appearance of skin rash, mucosal lesions or any other sign of hypersensitivity (4.4)
- Close observation for signs of bleeding whenever a combination with anticoagulants, thrombolytics, antiplatelets, anti-inflammatory drugs or SSRIs cannot be avoided (4.4)
- Review the need for temporary discontinuation before surgery, including tooth extraction (4.4)
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).
Related
Curated clinical cross-links plus same-class fallbacks.
- HEART Score for Major Adverse Cardiac EventsRecommendedChest Pain
- HAS-BLED ScoreRecommendedBleeding Risk
- CHADS₂ Score for AF Stroke RiskRecommendedStroke Risk
- Acute Heart Failure · ESC 2021 Heart Failure Guidelines; NICE NG106
- NSTEMI / Unstable Angina · ESC 2020 NSTEMI Guidelines; NICE NG185
- New-Onset Atrial Fibrillation · ESC 2020 AF Guidelines; NICE NG196
- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines