What is Prazosin?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 06 October 2019
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Prazosin is a hypertension medication a doctor may prescribe alone or with other medications to bring a patient's blood pressure down. This medication is also useful in the treatment of some other medical conditions. It is available in the form of tablets to be taken at precise dosage intervals. Patients should be aware that this medication can cause what is known as a first dose response, where the first dose taken results in severe side effects, but these are not repeated with future doses.

This medication works by acting on alpha receptors to relax the blood vessels. When people initially take prazosin, their heart rates can go up, as the body has adjusted to chronic high blood pressure, and the relaxation of the blood vessels will force the heart to work harder. The first dose response to the medication can include a sudden drop in blood pressure, along with fainting. Often, doctors advise patients to take the first dose before they go to bed, so this response will be less dangerous.

Side effects of prazosin include dizziness, fatigue, and fainting, especially when the medication is first started. As the patient's body adjusts, the side effects should resolve. If they do not, the patient may be sensitive to the medication. A doctor can try adjusting the dosage to see if this addresses the problem, or may switch the patient to another medication. Nasal congestion is also a common side effect.


A doctor may prescribe prazosin to a patient with urinary hesitation to relax the bladder muscles and make it easier to pee, especially in men with prostate enlargement. The medication is also useful in the management of nightmares associated with post-traumatic stress disorder. Patients with Raynaud's phenomenon, where circulation to the extremities falls, causing them to turn blue and numb, can also benefit from prazosin therapy. The relaxing effect on the blood vessels keeps even the small vessels at the ends of the extremities open, allowing blood to flow freely.

The safety of this drug in pregnancy and breastfeeding is not known. Some studies suggest it may not be safe in pregnancy. If high blood pressure in a pregnant patient is a concern, a doctor may explore safer medications and other methods for management before turning to prazosin. Pregnant patients on this medication should report any side effects to their doctors, and an obstetrician may recommend special screening during the pregnancy to identify complications as early as possible.


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