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About one billion people worldwide take regular aspirin, usually to prevent heart attacks or strokes. But a new study suggests a more tailored strategy is required.

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Daily aspirin reduces blood clots by inhibiting platelets, but yields only modest long-term reductions in heart attacks and strokes, although it remains the most widely used antiplatelet drug in routine practice. We suspected that the disparity between the effect of aspirin on platelets in laboratory studies and clinical benefits in practice might be due to the ‘one-dose-fits-all’ approach adopted in all trials and clinical practice, with possible under-dosing at high body-size and excess-dosing at low body-size. We hypothesised that standard low-dose aspirin (i.e. 75-100mg daily), which is widely used in UK and Europe, would be insufficient at high body-size, whereas higher doses (325mg daily is widely used in the USA) would be excessive at lower body-size. 

By studying detailed individual patient data from previous trials (with over 130,000 participants) we showed that standard low-dose aspirin (75-100mg daily) was indeed only effective in preventing heart attacks and strokes in people weighing less than 70kg and or with lower body mass index (BMI<25). In contrast, higher doses were only effective at weight above 70kg or at higher BMI. Effects on other outcomes, including cancer, were also dependent on body size.

Rothwell PM, Cook NR, Gaziano JM, Price JF, Belch JFF, Roncaglioni MC, Morimoto T, Mehta Z Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: analysis of individual patient data from randomised trials. Lancet 2018 4;392:387-399.

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