Aspirin is widely used for its analgesic and anti-inflammatory properties, and increasingly in recent years as antithrombotic treatment. Daily doses of 75–150 mg effectively inhibit the ability of blood platelets to synthesise thromboxane A₂ and stable prostaglandins during their lifespan in the circulation (7–10 days), resulting in inhibition of platelet function ex vivo (impaired platelet aggregation) and in vivo (prolonged skin bleeding time). Because platelets play an important role in thrombosis, aspirin has an antithrombotic effect.

Systematic reviews of randomised controlled trials of antiplatelet drugs (usually aspirin) have shown clinically worthwhile reductions in cardiovascular events (non-fatal myocardial infarction, stroke, and cardiovascular death) when these agents are used in the treatment of patients with acute ischaemia (myocardial infarction, unstable angina, stroke), when used as secondary prophylaxis in patients with chronic ischaemia (previous myocardial infarction, stroke or transient cerebral ischaemic attacks; stable angina; peripheral arterial disease), and when used as prophylaxis in patients withatrial fibrillation.1 ,2Antiplatelet treatment (usually with aspirin) is therefore recommended as prophylaxis of cardiovascular disease in these patient groups in national, evidence based guidelines in Scotland3 and the rest of the UK.4 However, as with all effective drugs, aspirin has adverse effects.