Over the next three weeks the journal is devoting 50 pages to overviews prepared by the Antiplatelet Trialists' Collaboration.*RF1-3* Altogether, some 300 randomised controlled trials assessing the potential benefits of antiplatelet treatment are considered. This editorial and the next one, by George Davey Smith and Matthias Egger,4 discuss some of the clinical and methodological implications of these landmark papers.

The first paper (p 81)1 reviews the efficacy of such treatments in preventing death, myocardial infarction, and stroke in patients with documented atherosclerosis (for example, unstable angina, or previous myocardial infarction, transient ischaemic attack, or stroke). This large overview confirms that antiplatelet treatment reduces vascular events by about a quarter in these high risk patients. Non-fatal myocardial infarction and stroke are reduced by one third; vascular deaths (from fatal myocardial infarction and stroke) fall by one sixth.

In this heterogeneous group of patients these benefits are apparent irrespective of age, sex, blood pressure, or the presence of diabetes. Aspirin alone, at doses ranging from 75 mg to 325 mg, seems as effective as any other antiplatelet regimen, with little risk of adverse side effects (such as gastrointestinal or intracerebral haemorrhage). The most effective dose of aspirin for long term treatment still needs to be …