To explore the “healthy user” and “healthy adherer” effects—hypothetical sources of bias thought to arise when patients who initiate and adhere to preventive therapies are more likely to engage in healthy behaviors than are other subjects.
The authors examined the association between statin initiation and adherence, and the subsequent use of preventive health services and incidence of clinical outcomes unlikely to be associated with the need for, or use of, a statin among older enrollees in two state-sponsored drug benefit programs.
After adjustment for demographic and clinical covariates, patients who initiated statin use were more likely to receive recommended preventive services than noninitiators matched on age, sex, and state (hazard ratio [HR]: 1.10, 1.06–1.14 for males, HR: 1.09, 1.07–1.11 for females) and appeared to have a lower risk of a range of adverse outcomes (HR: 0.87, 0.85–0.89) thought to be unrelated to statin use. Adherence to a statin regimen was also associated with increased rates of preventive service use and a decreased rate of adverse clinical outcomes (HR: 0.93, 0.88–0.99).
These results suggest that patients initiating and adhering to chronic preventive drug therapies are more likely to engage in other health-promoting behaviors. Failure to account for this relationship may introduce bias in any epidemiologic study evaluating the effect of a preventive therapy on clinical outcomes.