[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) › Prazosin [Pharmacology](https://durgical.com/en/pharmacology/) · [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) # Prazosin A short-acting alpha-1 blocker for high blood pressure. Its first dose can cause a sudden faint, so treatment always starts at the lowest strength. Updated 2026-11-01 - Class: [Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) - Receptor: Alpha-1 adrenergic receptors - ATC code: C02CA01 ◎**Alpha-1 adrenergic receptors**Prazosin ⓘ No structure of prazosin bound to its receptor is available; the figure shows doxazosin, a quinazoline blocker of the same family, in the binding site of the human alpha-1A adrenergic receptor. **Target in 3D:** Alpha-1 adrenergic receptors. PDB structure 9M4Q (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/9M4Q) · Drag to rotate · pinch to zoom ## Mechanism of action Prazosin is a quinazoline that competitively and reversibly blocks alpha-1 receptors on arterioles and veins, so peripheral resistance and venous return fall. Because it spares presynaptic alpha-2 receptors, reflex tachycardia is milder than with non-selective blockers. It also relaxes the smooth muscle of the prostate and bladder neck. - Prazosin blocks alpha-1 receptors on arterioles and veins - Norepinephrine can no longer constrict the vessels - Resistance and blood pressure fall; prostatic muscle relaxes ## Pharmacokinetics **Absorption** Oral; peak levels in about three hours (label) **Distribution** Highly bound to plasma proteins **Metabolism** Extensive metabolism in the liver **Half-life** About 2 to 3 hours (label), so it is taken more than once a day ## Indications - High blood pressure [Arterial hypertension →](https://durgical.com/en/conditions/arterial-hypertension/) - Other uses: benign prostatic hyperplasia [Benign prostatic hyperplasia →](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/) - Other uses: nightmares and sleep problems in post-traumatic stress disorder, Raynaud phenomenon ## Adverse effects ### Common - Dizziness and lightheadedness - Headache and drowsiness - Tiredness, weakness and lack of energy - Palpitations - Nausea, dry mouth and nasal congestion ### Serious (rare, important) - Syncope with sudden loss of consciousness, mostly after the first dose - Priapism - Intraoperative floppy iris syndrome during cataract surgery ## Contraindications - Known sensitivity to quinazolines or prazosin ## Key interactions **PDE-5 inhibitors (for example sildenafil)** Additive fall in blood pressure and symptomatic hypotension **Other antihypertensives and diuretics** Additive hypotension ## What is monitored - Blood pressure lying and standing, especially after the first dose or a dose increase - Dizziness and falls ## Nursing care - Before the first dose: teach that dizziness or fainting can happen in the first hours; treatment starts at the lowest strength. - Avoid driving or hazardous tasks after the first dose and after a dose increase. - Rise slowly from lying or sitting; sit or lie down if dizzy. - Before cataract surgery, tell the eye surgeon about alpha blocker use. - An erection lasting several hours is an emergency. ## Pregnancy and breastfeeding Human data are limited; it has been used, alone or with other drugs, in severe hypertension of pregnancy, and animal studies showed no malformations. ## Memory aid PrazoSIN: Syncope Is Number one after the first dose. ## Test yourself Think of the answer, then tap the question to see it. ## Why does prazosin treatment always start at the lowest strength? Because of the first-dose effect: marked orthostatic hypotension, sometimes with syncope, in the first hours after the first dose. ## Why does prazosin cause less reflex tachycardia than phentolamine? It is selective for alpha-1 receptors and spares presynaptic alpha-2 receptors, so norepinephrine release is not increased. ## Which drug combination with prazosin can cause symptomatic hypotension? PDE-5 inhibitors such as sildenafil, because both lower blood pressure. ## Which psychiatric use does prazosin have outside its labelled indication? Nightmares and sleep problems linked to post-traumatic stress disorder. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/prazosin/) ## Related drugs - [Doxazosin](https://durgical.com/en/pharmacology/doxazosin/) - [Terazosin](https://durgical.com/en/pharmacology/terazosin/) - [Tamsulosin](https://durgical.com/en/pharmacology/tamsulosin/) ## Related conditions - [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/) - [Benign prostatic hyperplasia](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/) [← Back to the class: Alpha blockers](https://durgical.com/en/pharmacology/classes/alpha-blockers/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - PRAZOSIN HYDROCHLORIDE capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7293cef3-ef9e-40dc-9995-875ef047f693) (DailyMed (U.S. National Library of Medicine), 2026); [Prazosin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682245.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C02CA01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), cap. 10 (McGraw Hill, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/prazosin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/prazosin/