How much aspirin should I take to prevent and treat heart attacks and strokes?
An ideal dose of aspirin is one that maximizes its benefits but minimizes side effects. However, the ideal dose of aspirin for primary or secondary prevention of ischemic strokes and heart attacks has not been established firmly.
In situations where an immediate antiplatelet effect is needed (for example, in the treatment of acute heart attacks, ischemic strokes, and unstable angina) aspirin at moderate doses (160–325 mg/day) will produce rapid and immediate antiplatelet effects. In the ISIS-2 trial, a dose of 160 mg/day given within 24 hours of the onset of symptoms of heart attack was shown to decrease deaths due to heart attacks by 23%. Therefore, this is the dose recommended for acute heart attacks and unstable angina.
At lower doses, such as 75 mg/d, the antiplatelet effect of aspirin can be achieved in several days instead of minutes. Since the risk of serious bleeding from aspirin is lower at lower doses, 75 mg/d is an appropriate dose for long-term primary and secondary prevention. Even though aspirin at doses as low as 40 mg/d has been shown to have anti-platelet effects, there is insufficient and inconclusive data to show that such low doses are effective in preventing heart attacks and ischemic strokes.
There also is no evidence that higher doses of aspirin, such as 1000 mg/day or higher, is more effective than lower doses. Some studies even suggest that higher doses may not be as effective as lower doses. Since the side effects of aspirin are more frequent with higher doses, doctors generally do not recommend higher doses for long-term use.
Who should take aspirin to prevent and treat heart attacks and strokes?
Even though aspirin is available without a doctor's prescription and has been used safely for many years by patients for fever and pain, patients should NOT take aspirin on a long-term basis without consulting with their doctor.
Aspirin prevents blood clots from forming inside arteries affected by atherosclerosis, but aspirin does not prevent atherosclerosis. Other measures (losing excess weight, controlling high blood pressure and diabetes, lowering LDL cholesterol, increasing HDL cholesterol, and stopping cigarette smoking) are necessary to prevent atherosclerosis.
Most doctors now recommend low doses of aspirin long-term for patients with advanced atherosclerosis for secondary prevention purposes. Such patients include those with:
- prior heart attacks
- prior strokes
- exertional and unstable angina
- TIAs (transient ischemic attack, mini-stroke)
- vascular procedures such as PTCA and CABG
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