Prazosin is used alone or in combination with other medications to treat high blood pressure. Prazosin is in a class of medications called alpha-blockers. It works by relaxing the blood vessels so that blood can flow more easily through the body.
Prazosin comes as a capsule to take by mouth. It usually is taken two or three times a day at evenly spaced intervals. The first time taking prazosin, you should take it before you go to bed. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take prazosin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
Your doctor will probably start you on a low dose of prazosin and gradually increase your dose.
Prazosin controls high blood pressure but does not cure it. Continue to take prazosin even if you feel well. Do not stop taking prazosin without talking to your doctor.
Prazosin is also used to treat benign prostatic hyperplasia (BPH, noncancerous enlargement of the prostate), congestive heart failure, pheochromocytoma (adrenal gland tumor), sleep problems associated with post-traumatic stress disorder (PTSD; an anxiety disorder in people who experience or witness a traumatic, life-threatening event), and Raynaud's disease (condition where the fingers and toes change skin color from white to blue to red when exposed to hot or cold temperatures). Talk to your doctor about the possible risks of using this medication for your condition.
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.
Before taking prazosin,
- tell your doctor and pharmacist if you are allergic to prazosin, alfuzosin (Uroxatral), doxazosin (Cardura), terazosin (Hytrin), or any other medications.
- tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention: beta-blockers such as propranolol (Inderal); medications for erectile dysfunction (ED) such as sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra);and other medications for high blood pressure.
- tell your doctor if you have narcolepsy (a sleep disorder that may cause extreme sleepiness, sudden uncontrollable urge to sleep during daily activities) or if you have or have ever had prostate cancer or liver disease.
- tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking prazosin, call your doctor.
- if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking prazosin. If you need to have eye surgery at any time during or after your treatment, be sure to tell your doctor that you are taking or have taken prazosin.
- you should know that this drug may make you drowsy or dizzy. Do not drive a car, operate machinery, or perform dangerous tasks for 24 hours after the first time you take prazosin or after your dose is increased.
- ask your doctor about the safe use of alcoholic beverages while you are taking prazosin. Alcohol can make the side effects from prazosin worse.
- you should know that prazosin may cause dizziness, lightheadedness, and fainting when you get up too quickly from a lying position. This is more common when you first start taking prazosin, when your dose is increased, or when another blood pressure medication is added to your treatment. To help avoid this problem, get out of bed slowly, resting your feet on the floor for a few minutes before standing up. If you experience these symptoms, sit or lie down. These symptoms may also occur if you drink alcohol, stand for long periods of time, exercise, or if the weather is hot. If these symptoms do not improve, call your doctor.
Follow your doctor's directions for your meals, including advice for a reduced salt (sodium) diet.
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Check with your doctor if you have missed two or more doses.
Prazosin may cause side effects. Tell your doctor if any of these symptoms or those listed in the SPECIAL PRECAUTIONS section are severe or do not go away:
Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:
- difficulty breathing
- fast, pounding, or irregular heartbeat
- chest pain
- painful erection of the penis that lasts for hours
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.
Symptoms of overdose may include:
- decreased reflexes
Keep all appointments with your doctor and the laboratory. Your blood pressure should be checked regularly to determine your response to prazosin.
Before having any laboratory test, tell your doctor and the laboratory personnel that you are taking prazosin.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.
Selected Revisions: September 1, 2010.