Effect of increased cost-sharing on oral hypoglycemic use in five managed care organizations: how much is too much?

Med Care. 2005 Oct;43(10):951-9. doi: 10.1097/01.mlr.0000178216.23514.b7.


Background: For patients with a chronic disease, increased cost-sharing for medications may lead to unintended consequences, including reduced use of medications essential for control of their disease.

Objective: The objective of this study was to estimate the effects of small ($1-6 per 30-day supply), moderate ($7-10), and large (>$10) increases in medication cost-sharing on 12-month trends in oral hypoglycemic (OH) use among adults with type 2 diabetes.

Methods: We conducted a quasiexperimental study using a time series with comparison group design. Data were obtained from computerized membership, benefit, and pharmacy dispensing data of 5 managed care organizations (MCOs). A total of 13,110 12-month episodes of OH use and a medication cost-sharing increase ("intervention") were matched with 13,110 that had no increase. The dependent variable was OH average daily dose (ADD) standardized to each episode's mean OH ADD in the 6-month preintervention period. The principal independent variable was change in cost per 30-day OH supply between the 6-month pre- and postintervention periods. Effects of changes in cost-sharing on OH ADD were estimated using segmented time series regression.

Results: Episodes with >$10 increase in cost-sharing had significantly (alpha=0.05) decreased OH ADD in the postintervention period. At 6 months after this increase, OH ADD had decreased by 18.5% from that predicted from the preintervention trend. Episodes with a $1 to $10 increase in cost-sharing and those with no increase in cost-sharing had significant linear increases in OH use over the 12-month period.

Conclusions: Large increases in medication cost-sharing were associated with immediate and persistent reductions in OH use. Small and moderate increases had little effect on OH use in the 6-month period after the increase.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Chronic Disease / drug therapy
  • Chronic Disease / economics
  • Cost Sharing*
  • Databases, Factual
  • Diabetes Mellitus, Type 2 / drug therapy*
  • Diabetes Mellitus, Type 2 / economics*
  • Episode of Care
  • Financing, Personal
  • Humans
  • Hypoglycemic Agents / administration & dosage
  • Hypoglycemic Agents / economics*
  • Hypoglycemic Agents / therapeutic use
  • Managed Care Programs / economics
  • Middle Aged
  • Patient Compliance / statistics & numerical data*
  • Prescription Fees*
  • Regression Analysis
  • Self Administration / statistics & numerical data*
  • United States


  • Hypoglycemic Agents