Is adherence to drug treatment correlated with health-related quality of life?

Background: Adherence to drug treatment and health-related quality of life (HRQL) are two distinct concepts. Generally one would expect a positive relationship between the two. Objectives: The purpose of this study was to assess the relationship between adherence and HRQL. Methods: HRQL was measured using the physical and mental summary measures of the RAND-12 (PHC-12, MHC-12), the SF-12 (PCS-12, MCS-12), HUI-2 and HUI-3. Adherence was assessed using Morisky's instrument. Three longitudinal datasets were used. One dataset included 100 hypertensive patients. Another dataset covered 199 high risk community-dwelling individuals. The third dataset consisted of 365 elderly patients. Spearman's correlation coefficients were used to assess association. Subgroup analyses by type of medication and inter-temporal analyses were also performed. Results: Correlation between adherence and PHC-12 ranged from 0.08 (p = 0.26) to 0.22 (p < 0.01). Correlations between adherence and MHC-12 ranged from 0.11 (p = 0.11) to 0.15 (p < 0.01). Similar results were observed using HUI-2, HUI-3, and SF-12 as well as by type of medication and in the lagged analyses. Conclusions: Correlations between HRQL and adherence were positive but typically weak or negligible in magnitude.