Long-term efficacy and safety of prazosin in essential hypertension.

The long-term efficacy and safety of prazosin plus a thiazide diuretic in severe hypertension has been evaluated in an open trial that is now in its fifth year. The combination is consistently effective in reducing diastolic blood pressure to 90 mm Hg or less. No side effects or adverse reactions have been observed except a "first-dose" fall in blood pressure, and there is no evidence of development of tolerance to the agent.