title: The impact of the Medicare Part D prescription benefit on generic drug use.
abstract: BACKGROUND
  Little information exists regarding the impact of Medicare Part D on generic drug use.
  
  
  OBJECTIVE
  To examine changes in the use of generic prescriptions attributable to Part D among a sample of Medicare beneficiaries.
  
  
  METHODS
  Difference-in-difference analysis of pharmacy claims of Part D enrollees and non-enrollees aged 67-79 years from 2005 to 2006. The final sample represented approximately 2.4 million unique subjects. Analyses were conducted separately for major therapeutic classes, limited to subjects filling at least one prescription within the class during 2005 and 2006, and adjusted for subject characteristics, prescription characteristics, socio-demographic characteristics measured through zipcode-linked Census data, baseline differences between Part D and non-Part D enrollees, and secular trends in generic use.
  
  
  RESULTS
  Generic drugs accounted for 58% of total prescriptions. Among the entire group of beneficiaries, there was a trend of increased generic drug use in 13 out of 15 drug classes examined. However, after adjusting for potential confounders, the growth rate of generic drug use was lower among Part D enrollees than among non-enrollees; enrollees were slightly less likely to fill prescriptions for generic drugs vs. brand-name drugs in 2006 compared to 2005 (odds ratio 0.95, 95% confidence interval 0.94-0.95).
  
  
  CONCLUSIONS
  Despite secular trends of increased utilization of generic drugs among both Part D enrollees and non-enrollees, the net impact of Part D among these beneficiaries was a modest decrease in the use of generic drugs. This finding, which is consistent with economic theory but contrary to several recent reports, highlights the complexity of assessing the impact of Part D on overall consumer welfare.
authors.affiliation: Department of Pharmacy, School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA.
authors.forename: James X
authors.initials: JX
authors.lastname: Zhang
authors.forename: Wesley
authors.initials: W
authors.lastname: Yin
authors.forename: Shawn X
authors.initials: SX
authors.lastname: Sun
authors.forename: G Caleb
authors.initials: GC
authors.lastname: Alexander
mesh_terms: D000368:Aged; D011307:Drug Prescriptions / Q000191:economics*; D017723:Drug Utilization Review / Q000379:methods / Q000639:trends; D016568:Drugs, Generic / Q000191:economics* / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007356:Insurance, Pharmaceutical Services / Q000191:economics / Q000639:trends; D008297:Male; D054524:Medicare Part D / Q000191:economics* / Q000639:trends; D011897:Random Allocation; D014481:United States
chemical_list: D016568:Drugs, Generic