Participation in a clinical trial enhances adherence and persistence to treatment: a retrospective cohort study.

Poor adherence to treatment is one of the major determinants of an uncontrolled blood pressure. Participation in a clinical trial may increase patient's adherence to treatment. This prompted us to investigate adherence and persistence profiles in patients with hypertension who had participated in a clinical trial, by collecting pharmacy refill data before, during, and after participation in the trial. Pharmacy refill data of 182 patients with hypertension who participated in the Home Versus Office Blood Pressure Measurements: Reduction of Unnecessary Treatment Study between 2001 and 2005 were obtained from 1999 until 2010. Refill adherence to treatment was compared for the periods before, during, and after this trial. Persistence to medication was investigated for the period after termination of the trial. Refill data were available for 22 600 prescriptions. Participation into the trial significantly increased refill adherence, from 90.6% to 95.6% (P<0.001). After the trial period, refill adherence decreased again to 91.8% (P<0.001), which did not differ from the adherence before the start of the trial (P=0.45). Except for adherence to trial medication, adherence to nontrial-related drugs also increased as a consequence of trial participation, from 77.6% to 89.6% (P<0.001). After termination of the trial, median persistence was 1424 days. Participants classified as adherent (adherence: >90%) were less likely to discontinue treatment compared with nonadherent participants (odds ratio: 0.66 [95% CI: 0.45 to 0.98]). Participation in a clinical trial significantly increases adherence to both trial-related and nontrial-related treatment, suggesting that participants in a trial are more involved with their conditions and treatments.