Methods for evaluating patient adherence to antidepressant therapy: a real-world comparison of adherence and economic outcomes

Med Care. 2006 Apr;44(4):300-3. doi: 10.1097/01.mlr.0000204287.82701.9b.


Objective: The objective of this study was to differentiate between 3 measures of antidepressant adherence with regard to the number of patients deemed adherent to therapy and the association between adherence and resource utilization.

Design and setting: The authors conducted a retrospective study of patients initiating selective serotonin reuptake inhibitor (SSRI) therapy for depression and/or anxiety between July 2001 and June 2002 in a large national managed care database.

Main outcome measures: Rates of 6-month SSRI adherence were measured by 3 different metrics: length of therapy (LOT), medication possession ratio (MPR), and combined MPR/LOT. Differences in resource utilization for each adherence metric were measured for patients deemed as 1) adherent, 2) nonadherent, 3) therapy changers, and 4) dose titraters.

Results: There were 22,947 patients meeting study criteria. Although statistically different, 6-month adherence rates were numerically similar across all methods (LOT, 44.6%; MPR, 43.3%; and MPR/LOT, 42.9%, P < 0.001); approximately 57% of patients were nonadherent to therapy. Regardless of metric, the adherent cohort incurred the lowest yearly medical costs, followed by the nonadherent, titrate, and therapy change cohorts (P < 0.001 between adherent cohort and all other cohorts). The LOT method produced the greatest difference in yearly medical costs between adherent and nonadherent patients (Dollars 511) followed by MPR/LOT (Dollars 432) and MPR (Dollars 423). When antidepressant prescription costs were added to medical costs, patients requiring a therapy change and titrating therapy incurred higher costs than adherent patients, whereas nonadherent and adherent patients incurred similar costs.

Conclusion: Regardless of adherence metric, approximately 43% of patients were adherent to antidepressant therapy, and adherent patients were associated with the lowest yearly medical costs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Antidepressive Agents, Second-Generation / economics
  • Antidepressive Agents, Second-Generation / therapeutic use*
  • Anxiety Disorders / drug therapy*
  • Anxiety Disorders / epidemiology
  • Anxiety Disorders / psychology
  • Cohort Studies
  • Comorbidity
  • Depressive Disorder / drug therapy*
  • Depressive Disorder / epidemiology
  • Depressive Disorder / psychology
  • Health Care Costs
  • Humans
  • Managed Care Programs
  • Mental Health Services / economics*
  • Mental Health Services / statistics & numerical data
  • Outcome Assessment, Health Care / economics*
  • Patient Compliance / statistics & numerical data*
  • Research Design
  • Retrospective Studies
  • Serotonin Uptake Inhibitors / economics
  • Serotonin Uptake Inhibitors / therapeutic use*
  • United States / epidemiology


  • Antidepressive Agents, Second-Generation
  • Serotonin Uptake Inhibitors