Medication adherence was measured at baseline in Systolic Blood Pressure Intervention Trial.

Twenty-one percent had low, 40% had medium, and 39% had high adherence.

Systolic blood pressure (BP) was <140 in 55%, 140–160 in 37%, and >160 in 9%.

Baseline adherence and systolic BP were weakly associated.

No interaction between adherence and number of antihypertensive medications on systolic BP control.