Medically reviewed on April 30, 2018.
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
Therapeutic Class: Cardiovascular Agent
Pharmacologic Class: Alpha-1 Adrenergic Blocker
Uses For This Medicine
Prazosin is used alone or together with other medicines to treat high blood pressure (hypertension). High blood pressure adds to the workload of the heart and arteries. If it continues for a long time, the heart and arteries may not function properly. This can damage the blood vessels of the brain, heart, and kidneys, resulting in a stroke, heart failure, or kidney failure. High blood pressure may also increase the risk of heart attacks. These problems may be less likely to occur if blood pressure is controlled.
Prazosin belongs to the general class of medicines called antihypertensives. It works by relaxing the blood vessels so that blood passes through them more easily. This helps to lower blood pressure. Prazosin may also be used for other conditions as determined by your doctor.
Prazosin is available only with your doctor's prescription.
Before Using This Medicine
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For prazosin, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to prazosin or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies have not been performed on the relationship of age to the effects of prazosin in the pediatric population. Safety and efficacy have not been established.
No information is available on the relationship of age to the effects of prazosin in geriatric patients.
|All Trimesters||C||Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.|
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with Medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking prazosin, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using prazosin with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Using prazosin with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Interactions with Food/Tobacco/Alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.
Other Medical Problems
The presence of other medical problems may affect the use of prazosin. Make sure you tell your doctor if you have any other medical problems, especially:
- Angina (chest pain) or
- Heart disease, severe or
- Postural hypotension (low blood pressure)—Use with caution. May make these conditions worse.
- Cataract surgery—An eye problem called Intraoperative Floppy Iris Syndrome (IFIS) has occurred in patients who are taking or who have recently taken prazosin when they are having cataract surgery. You should tell your ophthalmologist (eye doctor) before your surgery if you are taking prazosin.
- Kidney disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.
Proper Use of This Medicine
In addition to the use of prazosin, treatment for your high blood pressure may include weight control and changes in the types of foods you eat, especially foods high in sodium (salt). Your doctor will tell you which of these are most important for you. You should check with your doctor before changing your diet.
Many patients who have high blood pressure will not notice any symptoms of the condition. In fact, many patients may feel normal. It is very important that you take your medicine exactly as directed and that you keep your appointments with your doctor even if you feel well.
Remember that prazosin will not cure your high blood pressure, but it does help control it. You must continue to take it as directed if you expect to lower your blood pressure and keep it down. You may have to take high blood pressure medicine for the rest of your life.
To help you remember to take your medicine, try to get into the habit of taking it at the same time each day.
The dose of prazosin will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of prazosin. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For oral dosage form (capsules):
- For high blood pressure:
- Adults—At first, 1 milligram (mg) two or three times a day. Your doctor will slowly increase your dose as needed. However, the dose is usually not more than 20 mg per day.
- Children—Use and dose must be determined by your doctor.
- For high blood pressure:
If you miss a dose of prazosin, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Precautions While Using This Medicine
It is very important that your doctor check your progress at regular visits to make sure that prazosin is working properly and to check for unwanted effects.
Dizziness, lightheadedness, or fainting may occur, especially when you get up from a lying or sitting position suddenly. Getting up slowly may help. These symptoms are more likely to occur when you begin taking prazosin, or when the dose is increased.
You may also have dizziness, lightheadedness, or fainting if you drink alcohol, stand for a long time, exercise or if the weather is hot. While you are taking prazosin, be careful to limit the amount of alcohol you drink. Also, use extra care during exercise or hot weather.
Prazosin may cause some people to become dizzy, drowsy, or less alert than they are normally. Make sure you know how you react to prazosin before you drive, use machines, or do anything else that could be dangerous if you are dizzy, drowsy, or are not alert.
Make sure any doctor or dentist who treats you knows that you are using prazosin. Prazosin may affect the results of certain medical tests.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
If you are a man and experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis.
This Medicine Side Effects
Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur:More common
- Dizziness or lightheadedness, especially when getting up from a lying or sitting position
- fainting (sudden)
- Loss of bladder control
- pounding heartbeat
- swelling of the feet or lower legs
- Chest pain
- trouble breathing
- Painful or prolonged erection of the penis
Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:More common
- lack of energy
- Dryness of the mouth
- unusual tiredness or weakness
- Frequent urge to urinate
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
See also: Side effects (in more detail)
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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- Drug class: antiadrenergic agents, peripherally acting
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