Concern beliefs in medications: changes over time and medication use factors related to a change in beliefs. BACKGROUND: Concern belief in medication is a construct that may characterize patients' attitude toward managing medicines, and this could change with time. Understanding the factors that would impact a change in concern beliefs would be helpful in interventions that could reframe patients' perceptions about their medicines. OBJECTIVES: To examine if patient concern beliefs in medications change over time, assess the characteristics of individuals whose beliefs change, and determine what factors might impact a change in patient beliefs. METHODS: Secondary data analysis using 2 longitudinal studies. The first study was an Internet-based survey of Medicare enrollees pre-post Medicare Part D. The second study was a randomized controlled trial evaluating a medication management intervention among adults with physical limitations. Respondents were classified as those whose beliefs remained stable and those whose beliefs increased and decreased over 2 separate periods. Chi-square analysis examined significant differences across the groups. Multiple linear regressions examined factors that influence changes in patient beliefs. RESULTS: Among older adults, there were differences in perceived health status (χ(2)=26.05, P=.001), number of pharmacies used (χ(2)=17.41, P=.008), and number of medicines used after the start of Medicare Part D. There were no significant differences among adults with physical limitations. Among older adults, having an increased number of medicines over time and reporting a self-reported adverse effect to a physician were positively associated with an increase in concern beliefs in medication. Having an increase in adherence was associated with a decrease in concern beliefs over time. CONCLUSION: Concern beliefs in medications may contribute independent information about individuals' response to drug programs and policies. Outcomes of medication use may influence patient anxieties about medicines. The instability of patient concerns in medications that occurs with prescription drug coverage changes, and the emergence of adverse outcomes of medication use may provide insight into the development of individualized interventions.