Aspirin has clear benefits in cardiovascular disease. It reduces total mortality, cardiovascular mortality, and cardiovascular morbidity in people with cardiovascular disease or those at high risk of the disease; it is also cheap, relatively safe, and easy to use.1 So why does aspirin fail to work in some people who take it as prescribed? Research on this clinical “resistance” to aspirin has tried to assess whether the effect on the in vitro activation of platelets depends only on the dose and type of antithrombotic agent given, or whether some people respond poorly (“resist”) to a specific drug, as some people do to specific antibiotics. In the accompanying systematic review, Krasopoulos and colleagues assess whether resistance to aspirin is related to cardiovascular outcomes in people with cardiovascular disease.2

To date, most research has focused on whether aspirin resistance …