Medication adherence is one important determinant of health outcomes. Approximately one half of treatments for chronic disease are not taken as directed. Cost is one of several important causes of poor adherence and it is particularly important for vulnerable people. At least 2.4 million adult Canadians report cost related nonadherence to medications. 31 % of prescriptions in Quebec are not filled and those of highest cost are least likely to be filled. Providing full drug coverage may improve medication adherence and clinical outcomes, particularly for vulnerable individuals and those with chronic diseases.