Concern beliefs in medicines are patients' anxieties about the harmful effects of a specific prescribed medication. Three papers examined the importance of concern beliefs in medicine, specifically its relationship to patient outcomes such as self-reported adverse drug events (ADEs) and symptom attribution, and the factors that might drive a change in concern beliefs over time. For the first and second paper, a cross-sectional internet survey of Medicare enrollees who were English speakers, 65 years and older and enrolled in the Medicare Part D program was done. In the third paper, a longitudinal internet survey of the same sample was done before Medicare Part D in 2005 and after Medicare Part D in 2007, and adults 40 years and older with physical limitations were interviewed using telephone. Multiple logistic regressions showed that having stronger concern beliefs in medicine and more symptoms was related to self-reported ADE, rather than using an inappropriate medicine or the number of inappropriate medicines used. Using independent sample t-tests, concern beliefs in medicine were found to be unrelated to symptom attribution for any causal reason, irrespective of whether there was patient-clinician agreement on attribution. Multiple linear regressions showed that concern beliefs changed over time for some older adults and having an ADE in the past year was related to this change. Among adults with physical limitations, though concern beliefs changed for some individuals; only one factor included in this study, changes in number of medicines, was related to this change. Establishing the importance of concern beliefs in medicines as a socio-psychological variable to consider in medication use outcomes will enhance the understanding of clinical researchers and practitioners concerning the mechanism of ADEs and symptom reporting.