title: How patient cost-sharing trends affect adherence and outcomes: a literature review.
abstract: OBJECTIVE
  We sought to assess the relationship between patient cost sharing; medication adherence; and clinical, utilization, and economic outcomes.
  
  
  METHODS
  We conducted a literature review of articles and abstracts published from January 1974 to May 2008. Articles were identified using PubMed, Ovid, medline, Web of Science, and Google Scholar databases. The following terms were used in the search: adherence, compliance, copay, cost sharing, costs, noncompliance, outcomes, hospitalization, utilization, economics, income, and persistence.
  
  
  RESULTS
  We identified and included 160 articles in the review. Although the types of interventions, measures, and populations studied varied widely, we were able to identify relatively clear relationships between cost sharing, adherence, and outcomes. Of the articles that evaluated the relationship between changes in cost sharing and adherence, 85% showed that an increasing patient share of medication costs was significantly associated with a decrease in adherence. For articles that investigated the relationship between adherence and outcomes, the majority noted that increased adherence was associated with a statistically significant improvement in outcomes.
  
  
  CONCLUSIONS
  Increasing patient cost sharing was associated with declines in medication adherence, which in turn was associated with poorer health outcomes.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Eaddy
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Cook
authors.forename: Ken
authors.initials: K
authors.lastname: O'Day
authors.forename: Steven P
authors.initials: SP
authors.lastname: Burch
authors.forename: C Ron
authors.initials: CR
authors.lastname: Cantrell