The aim of this cross-sectional study was to quantify patients' personal beliefs about
the necessity of their prescribed medication and their concerns about taking it and
to assess relations between beliefs and reported adherence among 324 patients from
four chronic illness groups (asthma, renal, cardiac, and oncology). The findings revealed
considerable variation in reported adherence and beliefs about medicines within and
between illness groups. Most patients (89%) believed that their prescribed medication
was necessary for maintaining health. However, over a third had strong concerns about
their medication based on beliefs about the dangers of dependence or long-term effects.
Beliefs about medicines were related to reported adherence: higher necessity scores
correlated with higher reported adherence (r=0.21, n=324, p<0.01) and higher concerns
correlated with lower reported adherence (r=0.33, n=324, p<0.01). For 17% of the total
sample, concerns scores exceeded necessity scores and these patients reported significantly
lower adherence rates (t=-4.28, p<0.001). Stepwise multiple linear regression analysis
showed that higher reported adherence rates were associated with higher necessity-concerns
difference scores (beta=0.35, p<0.001), a diagnosis of asthma (beta= -0.31, p<0.001),
a diagnosis of heart disease (beta=0.19, p<0.001), and age (beta=0.22, p<0.001). Gender,
educational experience, or the number of prescribed medicines did not predict reported
adherence. Medication beliefs were more powerful predictors of reported adherence
than the clinical and sociodemographic factors, accounting for 19% of the explained
variance in adherence. These data were consistent with the hypothesis that many patients
engage in an implicit cost-benefit analysis in which beliefs about the necessity of
their medication are weighed against concerns about the potential adverse effects
of taking it and that these beliefs are related to medication adherence.