Drug Side Effect Symptoms and Adherence to Antihypertensive Medication

BACKGROUND: Non-adherence to antihypertensive medication increases the risk of uncontrolled hypertension. Antihypertensive drug-related symptoms (side effects) are frequently cited as a main cause of non-adherence, but with little support from prospective studies. We evaluated the association between drug side effects and prospective adherence to treatment. METHODS: We collected data on the number and dose of antihypertensive drugs at enrollment and at 3, 6, 9, and 12 months of follow-up in a cohort of 175 hypertensive patients starting or restarting antihypertensive treatment (mean age: 50 years; 58% women). During the follow-up visits, we gathered data on 24 side effects during the last month and the pill count adherence ratio (PCAR = pills taken out of number prescribed × 100) since the previous visit. The association between side effects at a visit and adherence through the next visit was estimated using mixed effect models. RESULTS: Eighty-five percent of the participants experienced side effects, and 34.5% became non-adherent (PCAR <80%). After adjusting for confounders, PCAR was 6.0 percentage points lower (P = 0.04) among individuals with number of side effects above the median value (4 symptoms). Also, in individuals with genitourinary side effects, PCAR was 7.1 percentage points lower (P = 0.02) than in those without such side effects. Specifically, PCAR was 6.5 (P = 0.06) and 7.6 (P = 0.01) percentage points lower among individuals with excessive urination and decrease in sexual drive, respectively. CONCLUSION: Antihypertensive drug side effects was associated with drug adherence but only excessive urination and decrease in sexual drive significantly predicted lower adherence. These symptoms could be used as markers to screen out patients at high risk of non-adherence.