Purpose: The purpose of this systematic review is to evaluate the evidence of the challenges and barriers to medication taking (adherence) and to summarize the interventions that improve medication taking in type 1 and type 2 diabetes mellitus.

Methods: PubMed, the Cochrane Collaborative, and the Health and Psychosocial Instruments databases were used to obtain articles identified by using the MeSH headings of diabetes, medication, oral hypoglycemic agents, oral antihyperglycemic agents, oral antidiabetic agents, insulin, adherence, medication taking, compliance, fears, treatment, and electronic monitoring. Only articles published in English between 1990 and May 7, 2007, and including individuals of all ages with type 1 or type 2 diabetes mellitus were included. Retrospective and prospective studies reporting adherence to medications using self-report, pill counts, medication possession ratios, and electronic monitoring devices were included. Database analyses of prescription records from various organizations or countries were included only if adherence to pharmacologic therapy was stated. Surveys and questionnaires assessing medication taking were also included. The data from the selected literature was abstracted independently. The various studies were grouped together based on the type of study conducted. Studies were not included if a specific measure of adherence to medication was not used or stated. The studies are presented in 3 tables according to design.

Conclusions: Several barriers to medication taking have been suggested for those with diabetes mellitus, although well-controlled trials to confirm and resolve these barriers are limited. Diabetes educators should be aware of the common barriers to medication taking (regimen complexity of more than 1 diabetes mellitus drug or more than 1 dose daily, depression, and remembering doses and refills) and provide screening and support to their patients to resolve barriers if they exist. Further studies are needed to test specific interventions to improve medication taking in diabetes.