The primary objective was to determine the effects of the Gastrointestinal Therapeutic System (GITS) formulation of Doxazosin when used in combination therapy with the 5 major classes of antihypertensive agents as measure by 24-hour diastolic blood pressure.

Inclusion Criteria:

• Eligible subjects were males or females ≥18 years of age with a diagnosis of primary essential hypertension and currently taking 1 or 2 individual antihypertensive agents
• Dosing for entry antihypertensive medication was at the accepted efficacious dose or the maximum tolerated dose and had to be stable for at least 4 weeks prior to study entry
• Subjects were required to have clinic sitting DBP ≥95 and ≤110 mmHg and SBP ≥140 and ≤180 mmHg as an average of 3 readings on their current antihypertensive therapy at visits 1 and 2

Exclusion Criteria:

Exclusion criteria included, but were not limited to:

• Subjects taking antihypertensive medications for other indications (i.e. arrhythrma, unstable angina, CHF, etc.)
• Orthostatic hypotension, defined as a decrease of at least 20 mmHg systolic or 1OmmHg diastolic pressure between sitting and standing blood pressures after 2 rmnutes, or known fluid depletion.