Effect of self-efficacy and social support on adherence to antihypertensive drugs.
STUDY OBJECTIVE
To determine the relationship between poor adherence and self-efficacy or social support after a pharmacist intervention.


DESIGN
Post-hoc analysis of data from two randomized controlled trials of physician-pharmacist collaborative interventions (6 and 9 mo, respectively) to improve blood pressure control.


SETTING
Eleven university-affiliated primary care clinics.


PATIENTS
Five hundred eighty-four patients (aged 21-85 yrs) with uncontrolled primary hypertension; 296 were in the intervention group and 288 were in the control group.


INTERVENTION
Pharmacists provided intensified hypertension management and drug adherence counseling to patients in the intervention group.


MEASUREMENTS AND MAIN RESULTS
Social support and self-efficacy questionnaires were administered at baseline and end-of-study visits. Patient adherence was monitored by using the Morisky self-reported adherence questionnaire. Self-reported adherence scores improved significantly in the control group (p=0.0053) but not in the intervention group; however, adherence at baseline in both groups was high. There were small, but significant, improvements in self-efficacy (p<0.04) and social support (p<0.05) scores in the intervention group but not the control group at the end of the study. Social support and, to a lesser extent, self-efficacy improved as a function of duration of study participation (9-mo vs 6-mo intervention), regardless of whether the patient received the intervention. Blood pressure control in both groups improved significantly at the end of the study; however, mean blood pressure was significantly lower in the intervention group (129.7/76.6 mm Hg) compared with the control group (140.8/78.9 mm Hg; p<0.0001 for systolic, p=0.032 for diastolic).


CONCLUSION
Social support and self-efficacy improved significantly in the intervention group at the end of the pharmacist intervention. Drug adherence was correlated with self-efficacy even though drug adherence did not improve significantly in the intervention group. The fact that social support and self-efficacy improved as a function of duration of study participation suggests that participation in a research study may have had a positive influence on these measures. Even though the changes in social support, self-efficacy, and drug adherence were modest, there was significantly better blood pressure control in the intervention group compared with the control group. These findings indicate that changes in drug adherence, self-efficacy, or social support probably played a minor role in the blood pressure outcomes in these studies.