This is a pharmacoepidemiology study using data from The Health Improvement Network (THIN) primary care database in the UK. Patients aged 50-84 years with evidence of ischemic heart disease or cerebrovascular disease, who were new users of low-dose ASA (75-300 mg/day) and who had received at least two low-dose ASA prescriptions for the secondary prevention of cardiovascular disease or cerebrovascular disease between 2000 and 2007 were identified from THIN. .