prazosin hydrochloride at a glance
Medicine class
Selective alpha-1 adrenoceptor blocker
Licensed uses
Hypertension, refractory congestive heart failure, Raynaud’s symptoms and urinary obstruction associated with benign prostate enlargement
How it is taken
An oral tablet taken exactly as prescribed
Key practical risk
Dizziness or fainting from a fall in blood pressure, particularly when treatment is started or changed
What is prazosin hydrochloride used for?
UK-licensed indications represented by the selected product are:
Essential or secondary hypertension, alone or with other blood-pressure-lowering treatment
Congestive heart failure that is resistant or refractory to conventional treatment
Symptomatic treatment of Raynaud’s phenomenon or Raynaud’s disease
Adjunctive relief of urinary obstruction caused by benign prostatic hyperplasia
Specialists sometimes use prazosin for PTSD-related nightmares. This is not a licensed UK indication; evidence suggests possible benefit but findings are inconsistent.
How does prazosin hydrochloride work?
Prazosin selectively blocks postsynaptic alpha-1 adrenoceptors. This relaxes arteries and veins, reducing resistance to blood flow. It also relaxes smooth muscle around the prostate and urethra, which can improve urinary flow.
prazosin hydrochloride preparations and strengths
Tablet
Route: Oral
Strengths: 0.5 mg
How to take prazosin hydrochloride
Take the tablet by mouth exactly as directed on the prescription label. Do not change or stop treatment without speaking to the prescriber. If dizziness or weakness occurs, lie down until it passes, then rise slowly. Avoid driving or machinery while affected.
Tell the cataract surgeon about current or previous prazosin use before eye surgery.
Arrange a further supply before tablets run out.
prazosin hydrochloride side effects
Common or expected effects
- Dizziness, faintness, drowsiness, headache or weakness
- Palpitations
- Nausea, vomiting, constipation, diarrhoea or dry mouth
- Blurred vision or nasal congestion
- Rash
- Ankle or leg swelling
- Passing urine more frequently
- Depression or nervousness
Get urgent medical advice
- Severe allergic reaction, including breathing difficulty or facial or throat swelling
- Marked low blood pressure, collapse or recurrent fainting
- A prolonged erection lasting longer than four hours
- New or severe chest pain
- Severe breathlessness
prazosin hydrochloride in pregnancy
Safety in pregnancy is not established. Limited human observations, including a small prospective series, have not identified outcomes above expected background rates, but the evidence is insufficient to confirm safety. Use requires an individual prescriber assessment that expected benefit outweighs potential risk.
prazosin hydrochloride while breastfeeding
Small amounts of prazosin have been detected in human milk. The product information advises caution, so breastfeeding should be discussed with the prescriber, particularly for a premature or unwell infant.
prazosin hydrochloride interactions
Important interactions mainly involve an additional fall in blood pressure.
PDE-5 inhibitors, including sildenafil, tadalafil and vardenafil
The combination can cause symptomatic or postural hypotension, with dizziness or fainting.
Beta blockers, calcium-channel blockers and ACE inhibitors
Blood pressure may fall substantially, requiring close clinical observation.
Other alpha-1 blockers
Combined treatment can increase hypotension and should not normally be used.
Common questions about prazosin hydrochloride
Answers are fully visible for fast scanning and source review.
Why can prazosin hydrochloride make me dizzy when I stand up?
Alpha-1 blockade relaxes blood vessels, so blood pressure can fall when changing position. Rise slowly and sit or lie down if dizziness develops.
Can prazosin hydrochloride cause fainting?
Yes. Syncope is reported, particularly when treatment begins or changes. Recurrent fainting or failure to recover requires urgent assessment.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.