[2] Common side effects include dizziness, sleepiness, swelling, nausea, shortness of breath, and abdominal pain.

[2] Severe side effects may include low blood pressure with standing, an irregular heart beat, and priapism.

Sympatholytic drugs, including prazosin and doxazosin, are used for nightmares and flashbacks in posttraumatic stress disorder (PTSD).

[citation needed] The Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) study stopped its arm of the trial looking at alpha blockers, because doxazosin was less effective than a simple diuretic, and because patients on doxazosin had a 25% higher rate of cardiovascular disease and twice the rate of congestive heart failure as patients on diuretics.

[11] Pfizer, aware of the results before publication, launched a marketing campaign in early 2000, and sales were largely unaffected, despite the dangers highlighted by the study.