The study is conducted using The Health Improvement Network database in the UK. Patients aged 40-84 years between January 1997 and December 2005 with a registration status of permanent or deceased, who were enrolled for at least 2 years with a GP and had 1 year of electronic prescription history. Patients with a code for cancer, peptic ulcer (both uncomplicated and complicated), upper GI bleeding, oesophageal varices, Mallory-Weiss disease, alcohol abuse, liver disease, or coagulopathies before beginning date were excluded from the source population. All patients in the study population were followed up until the end of the study period (December 2005), or until they reached the age of 85, died, met any of the exclusion criteria (including receiving a diagnosis of complicated peptic ulcer disease), or received a diagnosis of uncomplicated peptic ulcer disease.Patient records were manually reviewed to validate cases.