Adverse drug problems (ADPs) have become a serious and urgent health issue, causing significant morbidity, mortality, and economic burden to patients. A brief questionnaire asking patients how they coped with such problems can be a useful tool for providing timely interventions given information about their level of coping. The objective of this study was to develop a medication-problem coping scale to measure patients' coping responses to their ADP using item response theory (IRT). Candidate items were developed based on a comprehensive literature review that identified relevant items for measuring how patients coped with their ADPs. To fill in the content gaps, new items were added to the initial item pool. The items were administered to patients at community pharmacies that are incorporated into the Minnesota practice-based research network (PBRN). Psychometric analyses based on IRT were performed. Items that satisfied the model assumptions and achieved an adequate model fit remained in the final item bank. Reliability was assessed by analyzing the item information and test information. Convergent validity was evaluated by testing a priori formulated hypotheses about expected correlations between the coping scores on this scale and other related scales. A total of 140 patients participated in this study by answering all items. Confirmatory factor analysis suggested unidimensionality of 11 items. These items demonstrated adequate psychometric properties when calibrated using the two-parameter logistic (2PL) model. Reliability was evaluated by the information of the 11-item bank and a 6-item short-form. Respondents reporting their ADP as relatively large showed higher coping scores than those who perceived their ADP as small. Health literacy levels were higher in patients who sought out information as a coping strategy than in those who did not. However, there was unexpectedly little or no relationship between patients' coping levels and their coping self-efficacy. This study presents a medication-problem coping scale developed with IRT. The final item bank and its short-form may be applied to clinical samples to evaluate their usefulness.