Impact of a pharmacy benefit change on new use of mail order pharmacy among diabetes patients: the Diabetes Study of Northern California (DISTANCE)

Health Serv Res. 2015 Apr;50(2):537-59. doi: 10.1111/1475-6773.12223. Epub 2014 Aug 15.


Objective: To assess the impact of a pharmacy benefit change on mail order pharmacy (MOP) uptake.

Data sources/study setting: Race-stratified, random sample of diabetes patients in an integrated health care delivery system.

Study design: In this natural experiment, we studied the impact of a pharmacy benefit change that conditionally discounted medications if patients used MOP and prepaid two copayments. We compared MOP uptake among those exposed to the benefit change (n = 2,442) and the reference group with no benefit change (n = 8,148), and estimated differential MOP uptake across social strata using a difference-in-differences framework.

Data collection/extraction methods: Ascertained MOP uptake (initiation among previous nonusers).

Principal findings: Thirty percent of patients started using MOP after receiving the benefit change versus 9 percent uptake among the reference group (p < .0001). After adjustment, there was a 26 percentage point greater MOP uptake (benefit change effect). This benefit change effect was significantly smaller among patients with inadequate health literacy (15 percent less), limited English proficiency (14 percent less), and among Latinos and Asians (24 and 16 percent less compared to Caucasians).

Conclusions: Conditionally discounting medications delivered by MOP effectively stimulated MOP uptake overall, but it unintentionally widened previously existing social gaps in MOP use because it stimulated less MOP uptake in vulnerable populations.

Keywords: Mail order pharmacy; comparative effectiveness; difference-in-differences; health disparities; inverse probability treatment weighting; marginal structural model; pharmacy benefit designs.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aged
  • California
  • Deductibles and Coinsurance / statistics & numerical data
  • Diabetes Mellitus / drug therapy*
  • Female
  • Humans
  • Hypoglycemic Agents / economics*
  • Hypoglycemic Agents / therapeutic use*
  • Insurance, Pharmaceutical Services / statistics & numerical data*
  • Male
  • Middle Aged
  • Pharmaceutical Services / statistics & numerical data*
  • Postal Service*
  • Socioeconomic Factors


  • Hypoglycemic Agents