Prazosin Side Effects

Medically reviewed by Drugs.com. Last updated on Mar 31, 2025.

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 side effects

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

Less common side effects

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

Rare side effects

• 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 side effects

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

Less common side effects

• 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

Rare side effects

• 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.

General adverse events

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

Cardiovascular

• 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]

Other

• Common (1% to 10%): Lack of energy, weakness, asthenia
• Rare (less than 0.1%): Fever, pain
• Frequency not reported: Malaise^[Ref]

Gastrointestinal

• 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]

Psychiatric

• Common (1% to 10%): Depression, nervousness
• Uncommon (0.1% to 1%): Insomnia
• Rare (less than 0.1%): Hallucinations^[Ref]

Respiratory

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

Ocular

• 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]

Genitourinary

• Common (1% to 10%): Urinary frequency, impotence
• Rare (less than 0.1%): Incontinence, priapism^[Ref]

Dermatologic

• Common (1% to 10%): Rash
• Uncommon (0.1% to 1%): Diaphoresis, pruritus, urticaria
• Rare (less than 0.1%): Alopecia, lichen planus^[Ref]

Metabolic

• Common (1% to 10%): Edema^[Ref]

Musculoskeletal

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

Immunologic

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

Endocrine

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

Hepatic

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

Further information

Prazosin side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer