The purpose of this study was to evaluate the efficacy and safety of the addition of doxazosin in the treatment of hypertensive patients who are being treated on another antihypertensive drug. The open-labeled, noncomparative, multicenter study was carried out in 2363 male hypertensive outpatients > 40 years of age, under reasonable control with single antihypertensive drug treatment (diastolic blood pressure < 95 mm Hg), and diagnosed with benign prostatic hypertrophy. Doxazosin was started at a dose of 1 mg/day, which was increased at 2-week intervals to 2 mg/day and 4 mg/day. The study lasted 14 weeks. Blood pressure and heart rate were measured at each of the visits. At baseline and after 14 weeks of treatment, prostatism symptoms were quantified with the International Prostate Symptom Score and quality of life was determined with the American Urology Association Committee Guidelines. Adverse effects were recorded. At the fourth visit, when the patients were taking 4 mg of doxazosin, the blood pressure reduction was 10.7 +/- 3/7.1 +/- 7.1 mm Hg. The decrease in diastolic blood pressure was significantly more marked in patients treated with beta blockers than in patients on calcium antagonists or angiotensin-converting enzyme inhibitors. For systolic blood pressure, decreases were larger in patients treated with diuretics than with calcium antagonists or angiotensin-converting enzyme inhibitors. Prostatism symptoms decreased from 15 +/- 5.8 points to 7.9 +/- 4.3 points (p is less than 0.001) and quality of life improved. Tolerability was good, with only a 4.4% cumulative incidence of adverse effects related to doxazosin. The patients who experienced adverse effects were older and their final blood pressures were lower. The results of this open-label study suggest that the addition of doxazosin to another antihypertensive drug in hypertensive patients with benign prostatic hypertrophy is well tolerated and leads to a reduction in prostatic symptoms. The additional beneficial effects on blood pressure suggest that the use of doxazosin may provide a rational approach to this category of patients.(c)2001 Le Jacq Communications, Inc.