Email updates

Keep up to date with the latest news and content from ETE and BioMed Central.

Open Access Open Badges Methodology

Why is greater medication adherence associated with better outcomes

Arthur Hartz* and Tao He

Author Affiliations

Health Services Research, Huntsman Cancer Institute, University of Utah School of Medicine, Salt Lake City, UT 84112, USA

For all author emails, please log on.

Emerging Themes in Epidemiology 2013, 10:1  doi:10.1186/1742-7622-10-1

Published: 2 February 2013



Previous studies found an association of greater adherence to placebo medication with better outcomes. The present study tested whether this association was explained by any of the following factors: 1) adherence to other medications, 2) healthcare behaviors, 3) disease risk, or 4) predicted degree of adherence. Data included information on more than 800 risk factors from 27,347 subjects in two randomized controlled trials of hormone therapy in the Women's Health Initiative.


Greater adherence to placebo was not associated with colon cancer but was substantially and significantly associated with several diverse outcomes: death, myocardial infarction, stroke, and breast cancer. Adherence to hormone therapy was only weakly associated with outcomes. The WHI risk factors only poorly predicted degree of adherence, R2 < 4%. No underlying factors accounted for the association between placebo adherence and outcome.


The results suggest that adherence to placebo is a marker for important risk factors that were not measured by WHI. Once identified these risk factors may be used to increase the validity of observational studies of medical treatment by reducing unmeasured confounding.

Adherence; Placebo; Risk factors; Confounding; Observational studies