Objectives: The aim of this study was to determine the reasons why households kept unwanted medicines. Methods: A questionnaire was completed by patients or their families when they returned unused medicines for disposal to pharmacies in the community or to hospitals in Taipei. The reasons why medications were unused and the ways in which they were disposed were recorded and analyzed. Results: A total of 2,012 people completed the questionnaire. The way that they knew about returning unwanted medications was, ”walked by and saw the return box” (30.1%). The way they had previously disposed of unwanted medicines was to ”dispose in the trash can” (61.8%). The reasons for possessing unused medication were: ”felt well already” (35.7%) and ”forgot to take the medicines” (19.3%). The most commonly returned items were medications for ”gastrointestinal” (15.8%) and ”cardiovascular” (13.4%) problems. Conclusions: The results showed that medication adherence could be better. We suggest that pharmacists could do more patient education about chronic illness, following orders, not stopping the medication without asking the doctor; and, if they don't need medications for common illnesses, patients should discuss this with their doctor in order not to waste health insurance resources.