title: Does medication adherence following a copayment increase differ by disease burden?
abstract: OBJECTIVE
  To compare changes in medication adherence between patients with high- or low-comorbidity burden after a copayment increase.
  
  
  METHODS
  We conducted a retrospective observational study at four Veterans Affairs (VA) medical centers by comparing veterans with hypertension or diabetes required to pay copayments with propensity score-matched veterans exempt from copayments. Disease cohorts were stratified by Diagnostic Cost Group risk score: low- (<1) and high-comorbidity (>1) burden. Medication adherence from February 2001 to December 2003, constructed from VA pharmacy claims data based on the ReComp algorithm, were assessed using generalized estimating equations.
  
  
  RESULTS
  Veterans with lower comorbidity were more responsive to a U.S.$5 copayment increase than higher comorbidity veterans. In the lower comorbidity groups, veterans with diabetes had a greater reduction in adherence than veterans with hypertension. Adherence trends were similar for copayment-exempt and nonexempt veterans with higher comorbidity.
  
  
  CONCLUSIONS
  Medication copayment increases are associated with different impacts for low- and high-risk patients. High-risk patients incur greater out-of-pocket costs from continued adherence, while low-risk patients put themselves at increased risk for adverse health events due to greater nonadherence.
authors.affiliation: Division of General Internal Medicine, Department of Medicine, Duke University, Durham, NC, USA. virginia.wang@duke.edu
authors.forename: Virginia
authors.initials: V
authors.lastname: Wang
authors.forename: Chuan-Fen
authors.initials: CF
authors.lastname: Liu
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Bryson
authors.forename: Nancy D
authors.initials: ND
authors.lastname: Sharp
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Maciejewski
mesh_terms: D000367:Age Factors; D000928:Antidepressive Agents / Q000191:economics / Q000627:therapeutic use; D000959:Antihypertensive Agents / Q000191:economics / Q000627:therapeutic use; D015897:Comorbidity; D003669:Deductibles and Coinsurance / Q000191:economics*; D003863:Depression / Q000188:drug therapy / Q000191:economics; D003920:Diabetes Mellitus / Q000188:drug therapy; D006302:Health Services Research; D006801:Humans; D006973:Hypertension / Q000188:drug therapy; D007004:Hypoglycemic Agents / Q000191:economics / Q000627:therapeutic use; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors; D012959:Socioeconomic Factors; D014481:United States; D014493:United States Department of Veterans Affairs; D016903:Drug Monitoring
chemical_list: D000928:Antidepressive Agents; D000959:Antihypertensive Agents; D007004:Hypoglycemic Agents