Aspirin decreases the risk of heart attack and stroke by reducing the risk of clot formation in the blood. When you cut or injure yourself, the bleeding is stopped by the plugging of the damaged blood vessels with blood clots. These blood clots are formed by small blood cells known as platelets. Clot formation is triggered by the injured areas of the blood vessels where platelets stick together to form a clot.
Aspirin works by inhibiting platelet aggregation and formation of thrombi in arteries. Other antiplatelet drugs are clopidogrel, prasugrel and ticagrelor. Aspirin in cardiovascular prevention is used in low dose of 75mg daily which is much less than doses used in analgesia (as a pain killer).
Aspirin should not be used in children below the age of 16. Exemptions include certain situations after heart surgery and in Kawasaki disease when aspirin can be given on specialist recommendation.
The benefit of aspirin is greatest immediately after coronary event, revascularization or stroke but the treatment is normally continued lifelong. Aspirin used to be recommended in patients at high risk of heart attack or stroke (e.g. in diabetes or hypertension) before they actually had the event but because the beneficial effect is only minimal and is largely offset by increased risk of bleeding, aspirin is no longer recommended in primary prevention.