Prazosin

1 medicine

Prazosin is an alpha-1 blocker used for high blood pressure, urinary symptoms of an enlarged prostate, and PTSD-related nightmares; its first dose can cause a sudden drop in blood pressure and fainting, so it is taken at bedtime.

Minipress

Prazosin

1/2mg

Minipress is a heart blood pressure medication containing Prazosin, available as 1/2mg tablets.

from $0.56 / tablet View

Key facts

  • Prazosin is an alpha-1 blocker (brand name Minipress) that relaxes the muscle in blood vessel walls and in the prostate and bladder neck.
  • It treats high blood pressure, urinary symptoms of an enlarged prostate, and nightmares linked to post-traumatic stress disorder.
  • The first dose, or any dose increase, can cause a steep drop in blood pressure with dizziness or fainting. Take the first dose at bedtime, while lying down, and avoid driving for the next 24 hours.
  • Seek urgent care for fainting, a fast or irregular heartbeat, or a painful erection lasting more than 4 hours.

What prazosin treats

Prazosin lowers blood pressure that has not responded well enough to other treatments. It eases urinary symptoms of benign prostatic hyperplasia (an enlarged prostate), such as a weak stream, frequent urination, or a sense the bladder never fully empties. It is also widely used, based on strong clinical evidence, to reduce the frequency and intensity of nightmares in people with post-traumatic stress disorder.

How prazosin works

Prazosin blocks alpha-1 adrenergic receptors, which normally receive signals from noradrenaline that tell smooth muscle to tighten. With these receptors blocked, blood vessel walls relax and blood pressure falls, and the muscle around the prostate and bladder neck loosens so urine flows more easily. In the brain, reducing noradrenaline signaling is thought to calm the exaggerated arousal that drives PTSD nightmares.

Before you take it

  • Avoid prazosin if you have had an allergic reaction to it or to related alpha-blockers (terazosin, doxazosin).
  • Tell your prescriber about other blood pressure medicines, erectile dysfunction drugs (sildenafil and similar), and any history of fainting or very low blood pressure, since combining these intensifies the blood-pressure drop.
  • People with severe heart valve disease should discuss the risks with their prescriber before starting.
  • If you need cataract surgery, tell your eye surgeon you take prazosin, since it can cause a complication during the operation.

Side effects

Common effects include dizziness, headache, fatigue, nausea, nasal congestion, palpitations, and dry mouth, which often ease as your body adjusts.

Stop and seek urgent medical care for any of these:

  • Fainting or a sudden, severe drop in blood pressure.
  • A fast, irregular, or pounding heartbeat.
  • Chest pain or pressure that does not go away.
  • An erection lasting more than 4 hours.
  • Signs of a severe allergic reaction: rash, swelling, or difficulty breathing.

Safety essentials

  • The first-dose effect is the defining risk: take your first dose (and any increase) at bedtime, rise slowly from sitting or lying, and do not drive until you know how prazosin affects you.
  • Combining prazosin with other blood-pressure medicines, alcohol, or erectile dysfunction drugs increases the risk of a dangerous blood pressure drop.
  • Buy prazosin only from a licensed pharmacy to avoid counterfeit or substandard tablets.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.