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Prazosin Side Effects

Medically reviewed by Last updated on Mar 29, 2023.

Applies to prazosin: oral capsule.

Serious side effects of Prazosin

Along with its needed effects, prazosin 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 while taking prazosin:

More common

  • Dizziness
  • fast, irregular, pounding, or racing heartbeat or pulse
  • sleepiness

Less common

  • Blurred vision
  • chills
  • cold sweats
  • dizziness, faintness, or lightheadedness when getting up from lying or sitting position
  • swelling
  • trouble breathing


  • Bloating
  • constipation
  • darkened urine
  • decreased interest in sexual intercourse
  • fever
  • inability to have or keep an erection
  • indigestion
  • loss in sexual ability, desire, drive, or performance
  • loss of appetite
  • nausea
  • painful or prolonged erection of the penis for more than 4 hours
  • pains in the stomach, side, or abdomen, possibly radiating to the back
  • vomiting
  • yellow eyes or skin

Incidence not known

  • Arm, back, or jaw pain
  • chest pain, discomfort, tightness, or heaviness
  • confusion
  • cough
  • difficulty swallowing
  • eye pain
  • hives, itching, skin rash
  • puffiness or swelling of the eyelids or around the eyes, face, lips or tongue
  • slow or irregular heartbeat
  • unusual tiredness or weakness

Other side effects of Prazosin

Some side effects of prazosin 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

  • Headache
  • lack of energy
  • unusual drowsiness, dullness, or feeling of sluggishness

Less common

  • Bloody nose
  • diarrhea
  • discouragement
  • dry mouth
  • feeling of constant movement of self or surroundings
  • feeling sad or empty
  • increased need to urinate
  • loss of interest or pleasure
  • nervousness
  • passing urine more often
  • sensation of spinning
  • stuffy nose
  • trouble concentrating
  • trouble sleeping


  • Burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • continuing ringing or buzzing or other unexplained noise in the ears
  • difficulty in moving
  • hearing loss
  • increased sweating
  • loss or thinning of the hair
  • muscle pain or stiffness
  • pain in the joints
  • seeing, hearing, or feeling things that are not there

Incidence not known

  • Feeling of warmth
  • lack or loss of strength
  • redness of the face, neck, arms and occasionally, upper chest
  • swelling of the breasts or breast soreness in both females and males

For Healthcare Professionals

Applies to prazosin: compounding powder, oral capsule.


The most common adverse reactions were postural hypotension, dizziness, headache, drowsiness, lack of energy, weakness, palpitations, and nausea.[Ref]


Very common (10% or more): Postural hypotension (up to 14%)

Common (1% to 10%): Palpitations, tachycardia, orthostatic hypotension

Uncommon (0.1% to 1%): Angina pectoris

Rare (less than 0.1%): Bradycardia, flushing, hypotension, vasculitis

Frequency not reported: Angina exacerbation, myocardial infarction[Ref]

Nervous system

Very common (10% or more): Dizziness (up to 10.3%)

Common (1% to 10%): Drowsiness, headache, faintness, syncope, vertigo

Uncommon (0.1% to 1%): Paresthesia, tinnitus

Rare (less than 0.1%): Narcolepsy worsened[Ref]


Common (1% to 10%): Lack of energy, weakness, asthenia

Rare (less than 0.1%): Fever, pain

Frequency not reported: Malaise[Ref]


Common (1% to 10%): Constipation, diarrhea, dry mouth, nausea, vomiting

Uncommon (0.1% to 1%): Abdominal discomfort and/or pain

Rare (less than 0.1%): Pancreatitis[Ref]


Common (1% to 10%): Dyspnea, nasal congestion, epistaxis[Ref]


Common (1% to 10%): Depression, nervousness

Uncommon (0.1% to 1%): Insomnia

Rare (less than 0.1%): Hallucinations[Ref]


Common (1% to 10%): Blurred vision, sclera reddened

Uncommon (0.1% to 1%): Eye pain

Frequency not reported: Pigmentary mottling, serious retinopathy, cataract development, cataract disappearance[Ref]


Common (1% to 10%): Urinary frequency, impotence

Rare (less than 0.1%): Incontinence, priapism[Ref]


Common (1% to 10%): Rash

Uncommon (0.1% to 1%): Diaphoresis, pruritus, urticaria

Rare (less than 0.1%): Alopecia, lichen planus[Ref]


Common (1% to 10%): Edema[Ref]


Uncommon (0.1% to 1%): Arthralgia[Ref]


Rare (less than 0.1%): Allergic reaction, positive antinuclear antibody titer[Ref]


Rare (less than 0.1%): Gynecomastia[Ref]


Rare (less than 0.1%): Liver function abnormalities[Ref]


1. Product Information. Minipress (prazosin). Pfizer U.S. Pharmaceuticals. 2001.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Cerner Multum, Inc. Australian Product Information.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.