Doxazosin

Pronunciation: dox-AY-zoh-sin.

Generic name
doxazosin
Drug class
Alpha-1-adrenergic receptor antagonist (quinazoline class)
Form
Tablet (immediate-release, 1/2/4/8 mg) or extended-release tablet, depending on brand/market
Route
Oral
Legal status
Prescription-only

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Doxazosin mesilate (generic, IDT Australia Ltd) (5) · Full directory

What doxazosin is and how it works

Doxazosin is a prescription medicine that relaxes certain blood vessels and the muscle around the bladder outlet and prostate. It is used to lower blood pressure in hypertension and to relieve urinary symptoms caused by an enlarged prostate (benign prostatic hyperplasia, BPH). (1) (2)

Doxazosin has a well-known 'first-dose effect': your blood pressure can drop suddenly, especially after your very first dose, after any increase in dose, or if you restart it after missing several doses -- this can cause dizziness, weakness, or, rarely, fainting. Your clinician will start you on a low dose and increase it slowly for this reason. Always follow the exact starting dose and titration schedule your clinician gives you.

Mechanism of action: how doxazosin works

Doxazosin is a quinazoline-derivative, selective alpha-1-adrenergic receptor antagonist that blocks post-synaptic, post-junctional alpha-1 receptors, producing vasodilation (reducing peripheral vascular resistance and blood pressure) and relaxation of smooth muscle in the bladder neck and prostate (relieving BPH-related outflow obstruction). It is extensively hepatically metabolised, primarily via CYP3A4 with some CYP2D6/CYP2C9 involvement, and is highly protein bound. (1) (2) (4)

What doxazosin is used for

High blood pressure (hypertension)

Used alone or together with other blood-pressure medicines to lower high blood pressure. (1) (2)

Benign prostatic hyperplasia (BPH) symptoms

Used to relieve urinary symptoms (such as difficulty urinating, weak stream, or frequent urination) caused by an enlarged, non-cancerous prostate gland. (1) (2)

Before taking doxazosin

Do not take / not appropriate for

  • Do not take doxazosin if you are allergic to doxazosin or to related medicines called quinazolines (such as prazosin or terazosin). (all countries) (1) (2)
  • Do not take doxazosin if you have a history of fainting or severe dizziness on standing up (orthostatic hypotension) before starting, unless your clinician has specifically assessed this. (United Kingdom, European Union) (2)
  • If being treated for BPH, do not take doxazosin as your only medicine if you also have urinary tract blockage, long-term urinary infections, bladder stones, or an overflowing bladder/inability to pass urine (anuria) -- these need specific clinician assessment first. (United Kingdom, European Union) (2)
  • Do not increase your own dose or restart doxazosin on your own after missing several doses -- the first-dose blood-pressure-drop risk can return and your clinician needs to re-titrate you safely. (all countries) (1) (2)

Tell your clinician about

  • If you have ever fainted, felt very dizzy, or had low blood pressure on standing.
  • If you are scheduled for cataract or other eye surgery, even if you stopped doxazosin some time ago -- alpha-1 blockers can affect the iris during surgery (Intraoperative Floppy Iris Syndrome).
  • If you have liver problems -- doxazosin needs particular caution in people with impaired liver function.
  • If you take, or are prescribed, a medicine for erectile dysfunction (a PDE-5 inhibitor, such as sildenafil, tadalafil, or vardenafil) -- combining these can cause an additive blood-pressure drop.
  • If you take a strong CYP3A4-inhibiting medicine (for example clarithromycin, ketoconazole, itraconazole, or ritonavir) -- these can increase doxazosin levels in your body.
  • If you are pregnant, planning pregnancy, or breastfeeding.
  • If you notice a painful erection lasting several hours (priapism) -- this needs immediate medical attention.
(1) (2)

How to take doxazosin

  • Take doxazosin exactly as prescribed, once daily, with or without food, at the same time each day.
  • Your clinician will start you at the lowest dose (usually 1 mg once daily) to reduce the risk of a sudden blood-pressure drop.
  • Do not increase your dose yourself -- your clinician will raise it gradually, usually at 1-2 week intervals, only if needed.
  • Take your first dose, and any increased dose, at a time when you can sit or lie down afterward and avoid driving or operating machinery for the following 24 hours, in case you feel dizzy or faint.
  • If you have not taken doxazosin for several days or more, contact your clinician before restarting -- you may need to restart at the lowest dose.
(1) (2)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

If you miss a dose, take it as soon as you remember unless it is almost time for your next dose -- in that case, skip the missed dose and continue your regular schedule. Do not take a double dose. If you have missed several days of doxazosin, contact your clinician before taking your next dose, because you may need to restart at a lower dose to avoid a sudden blood-pressure drop.

Overdose

An overdose can cause a severe drop in blood pressure. If someone has taken too much doxazosin and feels very dizzy, faints, or collapses, call emergency services or a poison-control service immediately and, if they have fainted, lay them down with their legs raised (supine, head-down position) while waiting for help. (1) (2)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Dizziness.

What to notice: Dizziness.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (2)

Tiredness or drowsiness (somnolence).

What to notice: Tiredness or drowsiness (somnolence).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (2)

Headache.

What to notice: Headache.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Low blood pressure or a drop in blood pressure on standing (postural hypotension).

What to notice: Low blood pressure or a drop in blood pressure on standing (postural hypotension).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Palpitations or a fast heartbeat.

What to notice: Palpitations or a fast heartbeat.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Stomach pain, indigestion, dry mouth, or nausea.

What to notice: Stomach pain, indigestion, dry mouth, or nausea.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Swelling of the ankles or legs (oedema), chest discomfort, or general weakness.

What to notice: Swelling of the ankles or legs (oedema), chest discomfort, or general weakness.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (2)

Serious warnings

Signs of a sudden blood-pressure drop (the 'first-dose effect') — serious

Symptoms: Severe dizziness, light-headedness, weakness, or fainting (loss of consciousness) -- most likely shortly after your first dose, after a dose increase, or after restarting following a break in treatment.

Action: Sit or lie down immediately if you feel dizzy or faint. Avoid driving or hazardous tasks for 24 hours after your first dose, any dose increase, or restarting therapy. Contact your clinician if this happens, and never increase your own dose or restart on your own after missing doses. (1) (2)

Signs relevant to upcoming cataract or eye surgery — high caution

Symptoms: No symptoms beforehand -- this is a surgical planning issue, not something you will feel.

Action: Tell your eye surgeon and anaesthetist that you are taking, or have ever taken, doxazosin or a similar alpha-1-blocker medicine before any cataract or eye surgery, even if you stopped it some time ago -- it can cause Intraoperative Floppy Iris Syndrome (IFIS), which the surgical team needs to plan for. (1) (2)

A painful erection lasting several hours (priapism) — serious

Symptoms: A prolonged, painful erection not relieved by sexual activity.

Action: Seek immediate medical attention -- this is a medical emergency that can cause permanent damage if not treated promptly. (1) (2)

Interactions

  • Combining doxazosin with a PDE-5-inhibitor erectile-dysfunction medicine (such as sildenafil, tadalafil, or vardenafil) can cause an additive drop in blood pressure and symptomatic hypotension -- your clinician may recommend timing or dose adjustments. (1) (2)
  • Strong CYP3A4-inhibiting medicines (for example clarithromycin, ketoconazole, itraconazole, or ritonavir) may increase doxazosin levels in the body, raising the risk of low blood pressure and its symptoms. (1) (2)
  • Doxazosin can add to the blood-pressure-lowering effect of other alpha-blockers and other antihypertensive medicines. (2)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Available human data are not sufficient to establish whether doxazosin raises the risk of birth defects or miscarriage; animal studies at very high doses reduced fetal survival, though no clear teratogenic effect was seen at therapeutic doses. Use only if your clinician judges the potential benefit outweighs the potential risk. (1) (2) (3) (4) (5) (6)

Breastfeeding

Doxazosin passes into breast milk at very low levels (estimated relative infant dose under 1%), but there is no information on effects on a breastfed infant or on milk supply. Discuss with your clinician before use while breastfeeding. (1) (2) (3) (4) (5) (6)

Children

No specific paediatric dosing guidance was identified in the sources reviewed for this dossier -- doxazosin is used in adults for hypertension and BPH, a condition that does not occur in children. (1) (2) (3) (4) (5) (6)

Elderly

No specific dose adjustment based on age alone is described in the sources reviewed, but older adults may be more prone to postural-hypotension symptoms and should be monitored carefully, especially when starting or increasing the dose. (1) (2) (3) (4) (5) (6)

Hepatic Impairment

Doxazosin should be given with particular caution in people with impaired liver function; the US label specifies monitoring blood pressure and symptoms of hypotension in Child-Pugh Class A and B hepatic impairment. (1) (2) (3) (4) (5) (6)

Renal Impairment

No specific dose adjustment based on kidney function alone is described in the sources reviewed for this dossier. (1) (2) (3) (4) (5) (6)

Monitoring

Before starting

  • Baseline blood pressure and standing (orthostatic) blood pressure
  • Assessment for prostate cancer before starting treatment for BPH symptoms
  • Review of current medicines for PDE-5 inhibitors or strong CYP3A4 inhibitors

During treatment

  • Blood pressure monitoring for at least 6 hours following the initial dose and each dose increase, per the US label.
  • Ongoing routine blood-pressure monitoring throughout treatment.
  • Watch for dizziness, fainting, or symptoms of low blood pressure, especially after dose changes.
  • Tell any surgical/eye-care team about current or past doxazosin use before cataract surgery.
(1) (2)

Storage

Store at room temperature, away from moisture and direct light, out of reach of children, following the exact instructions on your product's label.

Study the drug class: Alpha blockers

Professional information

Clinician-facing context only, sourced from the current US FDA Cardura prescribing information and the UK Doxazosin SmPC; verify against the current full label for the specific product and formulation before prescribing.

United States

Indication: Hypertension and BPH

Dose summary: Hypertension: initial 1 mg once daily, may double up to max 16 mg/day. BPH: initial 1 mg once daily, titrate at 1-2 week intervals to max 8 mg/day.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (1)

United Kingdom / European Union

Indication: Hypertension and BPH

Dose summary: Hypertension: initial 1 mg, titrate to 2 mg then 4 mg over 1-2 week intervals; max 16 mg/day. BPH: initial 1 mg, titrate to 2 mg then 4 mg (max 8 mg); usual dose 2-4 mg daily.

Renal context: No specific renal dosing guidance identified in the sources reviewed. (2)

Mechanism of action

Hepatic guidance

Administer with particular caution in hepatic impairment; monitor blood pressure and symptoms of hypotension in Child-Pugh Class A and B impairment per the US label.

Overdose note

Overdose is managed with supine, head-down positioning, volume expansion, and vasopressors if needed, with renal-function monitoring; doxazosin is highly protein bound so dialysis is not indicated. (1) (2) (4)

Frequently asked questions

Is doxazosin available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes. It is sold under many brand names -- Cardura/Cardura XL (United States, United Kingdom), Cardular PP/Uro (Germany), Cardura and generics (Canada), generic doxazosin mesilate tablets (Australia, since the original Carduran brand was discontinued in 2019), and Apo-Doxazosin (New Zealand) -- and is authorised and currently marketed in all 6 of these countries/regions. (1) (2) (3) (4) (5) (6)

Why do I have to start at such a low dose?

Doxazosin can cause a sudden, significant drop in blood pressure -- sometimes called the 'first-dose effect' -- especially after the very first dose or any dose increase. Starting at 1 mg and increasing slowly, usually every 1-2 weeks, helps your body adjust and reduces the risk of severe dizziness or fainting. (1) (2)

Why should I avoid driving after my first dose or a dose increase?

Because doxazosin can cause dizziness or, rarely, fainting shortly after your first dose or after a dose increase, US labelling specifically advises avoiding driving or hazardous tasks for 24 hours after these events, until you know how the medicine affects you. (1)

Do I need to tell my eye surgeon I take doxazosin?

Yes. Doxazosin and other alpha-1-blocker medicines can cause Intraoperative Floppy Iris Syndrome (IFIS) during cataract surgery, even if you stopped the medicine some time ago. Always tell your eye surgeon and anaesthetist about current or past use. (1) (2)

What is the mechanism of action of doxazosin?

Doxazosin is a quinazoline-derivative, selective alpha-1-adrenergic receptor antagonist that blocks post-synaptic, post-junctional alpha-1 receptors, producing vasodilation (reducing peripheral vascular resistance and blood pressure) and relaxation of smooth muscle in the bladder neck and prostate (relieving BPH-related outflow obstruction). It is extensively hepatically metabolised, primarily via CYP3A4 with some CYP2D6/CYP2C9 involvement, and is highly protein bound. (1) (2) (4)

What is the generic name of Doxazosin?

The generic name is doxazosin. (1) (2)

What class of drug is doxazosin?

Doxazosin is classed as: Alpha-1-adrenergic receptor antagonist (quinazoline class). (1) (2)

References

  1. CARDURA (doxazosin mesylate) tablets -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information · United States · accessed 2026-07-30 · source 1
  2. Doxazosin 4mg Tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom · United Kingdom · accessed 2026-07-30 · source 2
  3. Cardular PP 4 mg / 8 mg Retardtabletten -- Fachinformationfachinfo.de (German professional-information register) -- Viatris Healthcare GmbH · European Union (Germany) · accessed 2026-07-30 · source 3
  4. CARDURA (doxazosin mesylate) Product Monograph; current generic doxazosin products (APO-DOXAZOSIN, TEVA-DOXAZOSIN, JAMP-DOXAZOSIN)Health Canada product monograph register (pdf.hres.ca) -- AstraZeneca Canada Inc. / current generics via Health Canada Drug and Health Products Portal · Canada · accessed 2026-07-30 · source 4
  5. Doxazosin mesilate Tablets 1 mg / 4 mg / 8 mg -- ARTG entries (238895 / 238897 / 238898)Therapeutic Goods Administration (TGA), Australia -- Australian Register of Therapeutic Goods (ARTG) · Australia · accessed 2026-07-30 · source 5
  6. Doxazosin Tablets (Apo-Doxazosin) 2mg/4mg -- New Zealand Data SheetMedsafe (New Zealand regulator) -- approved data sheet · New Zealand · accessed 2026-07-30 · source 6

Brand names by country

Single-ingredient doxazosin names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Cardura8 mg, 2 mg, 4 mg, 1 mg · viatris specialty llc

United Kingdom

  • Cardura / Cardura XL (2)MHRA licensed emc smpc confirmed · 1 mg, 2 mg, 4 mg, 8 mg · Pfizer (historic) / various generics
  • Doxazosin (generic) (2)MHRA licensed emc smpc confirmed · 1 mg, 2 mg, 4 mg · Various generic manufacturers

Canada

  • CARDURA-1

Australia

  • Doxazosin mesilate (generic, IDT Australia Ltd) (5)TGA ARTG active registration confirmed · 1 mg, 4 mg, 8 mg · IDT Australia Ltd

New Zealand

  • Apo-Doxazosin (6)Medsafe approved data sheet confirmed · 2 mg, 4 mg · Apotex
View brands in additional countries.

European Union

Cardular PP / Cardular Uro (3), Doxazosin-ratiopharm / Doxazosin AbZ / Doxazosin-CT / Doxazosin 1 A Pharma (generics) (3)

This page provides general reference information about doxazosin and is not a substitute for advice from the clinician managing your treatment. All dosing, titration, and treatment decisions should be made with your prescriber or pharmacist.

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