To evaluate the relation between adherence to drug therapy, including placebo, and
mortality.
Meta-analysis of observational studies.
Electronic databases, contact with investigators, and textbooks and reviews on adherence.
Review methods Predefined criteria were used to select studies reporting mortality
among participants with good and poor adherence to drug therapy. Data were extracted
for disease, drug therapy groups, methods for measurement of adherence rate, definition
for good adherence, and mortality.
Data were available from 21 studies (46,847 participants), including eight studies
with placebo arms (19,633 participants). Compared with poor adherence, good adherence
was associated with lower mortality (odds ratio 0.56, 95% confidence interval 0.50
to 0.63). Good adherence to placebo was associated with lower mortality (0.56, 0.43
to 0.74), as was good adherence to beneficial drug therapy (0.55, 0.49 to 0.62). Good
adherence to harmful drug therapy was associated with increased mortality (2.90, 1.04
to 8.11).
Good adherence to drug therapy is associated with positive health outcomes. Moreover,
the observed association between good adherence to placebo and mortality supports
the existence of the "healthy adherer" effect, whereby adherence to drug therapy may
be a surrogate marker for overall healthy behaviour.