Low adherence was the most common cause of poor blood pressure control in patients with apparent resistant hypertension, being twice as frequent as secondary causes of hypertension. Incomplete adherence was far more common than complete nonadherence; thus, assessment of adherence in patients on multiple drug regime is only reliable when all drugs are included in assessment. Assessing adherence by toxicological urine screening is a useful tool in detecting low adherence, especially in the setting of multidrug regimen as a cause of apparently resistant hypertension.