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Prazosin Side Effects

In Summary

Commonly reported side effects of prazosin include: dizziness. Other side effects include: syncope and drowsiness. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to prazosin: oral capsule, oral tablet

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 or lightheadedness, especially when getting up from a lying or sitting position
  • fainting (sudden)
Less common
  • Loss of bladder control
  • pounding heartbeat
  • swelling of the feet or lower legs
  • Chest pain
  • trouble breathing
Incidence not known
  • Painful or prolonged erection of the penis

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 Less common
  • Dryness of the mouth
  • nervousness
  • unusual tiredness or weakness
  • Frequent urge to urinate
  • nausea

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. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

2. Cerner Multum, Inc. "Australian Product Information." O 0

3. "Product Information. Minipress (prazosin)." Pfizer US Pharmaceuticals, New York, NY.

Some side effects of prazosin may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.