Table 1.

Studies Reporting on the Association between Polypharmacy and Medication Adherence in Older Adults in the United States, 1998–2011

Citation	Study Design	Sample Description	Measure of Adherence	Polypharmacy Definition	Key Polypharmacy Findings
Chapman et al (2008)	Observational cohort	Adults aged ≥ 65 years who initiated treatment with both AH and LL therapy within a 90-day period	Medication possession ratio (cutoff 80%)	# of prescription medications	Adherence rate was decreased with taking more medications (AOR 0.43 for ≥ 6 medications vs 0–1 medication; 95% CI 0.36 to 0.50; P<0.001).
Choudhry et al (2011)	Observational cohort	Patients prescribed a statin or an ACE-inhibitor (2 separate cohorts) from a large pharmacy benefit manager	Proportion of days covered (also assessed therapeutic complexity)	# of prescription medications	Adherence was decreased with a greater number of medications in both cohorts (statin users: adjusted % change in adherence per additional medication, 0.89, P<0.001; ACE-inhibitor users: adjusted % change in adherence per additional medication, 0.69, P<0.001).
Gazmararian et al (2006)	Observational cohort	Adults aged ≥ 65 years with coronary heart disease, diabetes, hyper-lipidemia, and/or HTN	Cumulative medication gap less than 20%	# of oral prescription medications (≤ 3 vs >3)	Multivariate analysis showed that those who took more medications had a lower odds of having nonadherence compared to those taking less medication (AOR 0.77; 95%, CI 0.73 to 0.95) after controlling for health literacy, age, race, sex, and education.
Grant et al (2003)	Cross-sectional	Patients with diabetes (mean age 66 years) receiving primary care	Self-reported diabetes-related medication adherence	# of prescription medications	Adherence was not significantly associated with the number of diabetes- related medications.
Gray et al (2001)	Observational cohort	Adults aged ≥ 65 years receiving home health care following hospitalization for medical illness	Underadherence: at least one medication < 70%; Overadherence: at least one medication > 120%	# of prescription medications; Taking a drug ≥3 times/day	Multivariable analysis showed that underadherence was significantly associated with greater medication use (AOR 1.16, 95% CI 1.03 to 1.31) after controlling for demographic, health- related and medication-related covariates.
Ownby et al (2006)	Cross-sectional	Patients with memory disorders cared for at a memory disorders clinic	Caregivers’ reports of patients’ medication adherence	# of prescription medications	Adherence was not found to be associated with the number of medications.
Turner et al (2009)	Cross-sectional	Adults aged ≥ 70 years with HTN	Self-reported not missing any medication in the past 3 months	Antihypertensive regimen complexity ≥4 medications)	Adherence was significantly negatively 4 associated (less likely) with having ≥ 4 antihypertensive medications in regimen (AOR 0.23; 95% CI, 0.08 to 0.72).
Stoehr et al (2008)	Cross-sectional	Adults aged ≥ 65 years cared for in 7 private office practices	Global judgment by research nurses (ie, dichotomous outcome, yes/no) after a home visit	# of prescription medications (≥ 5 vs < 5); Dosing frequency(≥4 vs <4 times/day)	Adherence was negatively associated with a greater number of prescription medications (OR 0.45; 95% CI, 0.21 to 0.95; P=0.04).
van Bruggen et al (2009)	Cluster-RCT	Patients with diabetes (mean age ~67 years) receiving primary care (Netherlands)	Medication possession ratio (cutoff 80%)	# of prescription medications	Adherence to blood pressure lowering drugs was negatively associated with a greater number of prescription medications (AOR 0.84; 95% CI 0.78–91; P<0.0001), however, adherence was not significantly associated with the number of oral blood glucose or cholesterol lowering drugs.