OBJECTIVES: To analyze the add-on and switch patterns for patients who dispensed platelet aggregation inhibitors, excluding heparin (acetylsalicylic acid, clopidogrel, and dipyridamole) in the South-West region of Sweden. METHODS: This was a retrospective database study of medication utilization amongst patients from the South-West region of Sweden (1.5 million inhabitants). All patients who dispensed platelet aggregation inhibitors (B01AC), excluding heparin, from 2006 to 2009 were included in the study. A dispatch was classified as new, switch, add-on, or continuation. All dispatches were annotated, at the ATC level, as either new (no other anticoagulant within 105 days), add-on (another anticoagulant dispatched both before and after), switch (another anticoagulant dispatched before, but not after), or continuation (dispatched same ATC-code within 105 days). RESULTS: 163 330 patients had at least one B01AC filled prescription. The total number of dispatches for these patients were 3 327 499. 96% of all patients had been dispatched acetylsalicylic acid (ASA), 11% clopidogrel and 6% dipyridamole. ASA was dispatched as a new prescription in 17% of all dispatches, in <0.5% as add-on, <0.5% as switch, and in 83% as continuation. For clopidogrel the distribution was 17% (new), 4% (add-on), 3% (switch), and 77% (continuation). For dipyridamole the distribution was 7%, 18%, 8%, and 68%. CONCLUSIONS: Not surprisingly ASA was by far the most common treatment. ASA and Clopidogrel both had first line treatment profiles, of which it was most pronounced for ASA (<1% add-on or switch). Dipyridamole is used more as an add-on or switch therapy with 18% as add-on, 8% as switch, and only 7% as new dispatches.