Indiana University-Purdue University Indianapolis (IUPUI) / Medication adherence remains a problem among Type-2 diabetes (T2D) patients despite availability of effective treatments. Three analyses of extant data sets were conducted to examine barriers to using medication as prescribed as an alternate method to assess medication adherence: 1) development and psychometric evaluation of the Murage-Marrero-Monahan-Medication barriers (4M) scale to assess patients’ perceived barriers; 2) patient demographic factors associated with barriers to using medication as prescribed, and 3) the association between patients’ perceived barriers to medication use and cardiovascular disease (CVD) risk factor control.Twelve focus groups and a cross-sectional study of 362 T2D patients contributed to develop and evaluate psychometric properties of the 4M scale. A cross-sectional survey of 964 T2D patients was used for the other two studies. Analysis of covariance identified demographic factors associated with reported barriers. Multivariable logistic regression was used to identify barriers associated with CVD risk factors (glucose, blood pressure and lipids) categorized as either poor or good control. Exploratory factor analysis with Varimax rotation resulted in a 19-item 4M scale with acceptable psychometric properties. As a five-domain (or single-domain) structure, coefficient alpha ranged from 0.70 to 0.83 (0.92). Both structures demonstrated discriminant validity and known-group validity. Age was inversely associated with all identified barriers while income was inversely associated with poor communication with providers and side effects. A unit increase in the overall barrier mean score on the 4M scale was associated with 92% increase in the odds of having poor control of two or more CVD risk factors compared to good control of all three risk factors (adjusted OR=1.92, 95% CI: 1.16–3.17; p<0.05). The 4M scale demonstrated acceptable psychometric properties in assessing barriers to using medication among T2D patients. Poor medication adherence has been previously associated with CVD risk. In this study, greater barriers were associated with poorer control of CVD risk factors making barriers a potential alternative to medication adherence, whose current assessment methods are limited. The 4M scale has the advantage to identify specific barriers inhibiting medication use that can facilitate patient-provider discussions and the development of targeted interventions. / Some parts of this dissertation work were jointly funded by Program Announcement 04005 from the Centers for Disease Control and Prevention (Division of Diabetes Translation) and the National Institute of Diabetes and Digestive and Kidney Diseases. The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the funding agency(s).