Alpha blockers are a type of blood pressure medicine. Alpha blockers lower blood pressure by keeping a hormone called norepinephrine from tightening the muscles in the walls of smaller arteries and veins. As a result, the blood vessels remain open and relaxed. This improves blood flow and lowers blood pressure.

Alpha blockers also relax other muscles throughout the body. So, these medicines are sometimes used to improve urine flow in older men with prostate problems.

Alpha blockers are either short-acting or long-acting medicines. Short-acting medicines work quickly, but their effects last only a few hours. Long-acting medicines take longer to work, but their effects last longer. The alpha blocker that's best for you depends on your health and the condition being treated.

Alpha blockers also are called alpha-adrenergic blocking agents, alpha-adrenergic antagonists, adrenergic blocking agents, alpha-blocking agents and alpha-1 blockers.

Examples of alpha blockers used to treat high blood pressure include:

• Doxazosin (Cardura).
• Prazosin (Minipress).
• Terazosin.

Alpha blockers typically aren't the first treatment option for high blood pressure. Instead, they're used together with other medicines, such as diuretics, when high blood pressure is difficult to control.

Alpha blockers are sometimes given to prevent, treat or improve symptoms of an enlarged prostate, also called benign prostatic hyperplasia.

When you start taking an alpha blocker, you might have low blood pressure and dizziness. This can make you faint when you get up from sitting or lying down to standing. As a result, the first dose is often taken at bedtime.

Other side effects might include:

• Dizziness.
• Headache.
• Fast or pounding heartbeat.
• Weakness.

Before taking an alpha blocker, be sure your health care team knows about other medicines you take. Alpha blockers may affect how some other medicines work. Be sure to mention if you take any beta blockers, calcium channel blockers or medicines for erectile dysfunction.

Alpha blockers may improve total cholesterol. But some research suggests that long-term use of some alpha blockers might increase the risk of heart failure.

Talk to your health care team if you have any questions about the medicines you take.