An alpha-blocker
Doxazosin
An alpha-blocker used to ease prostate symptoms in men, and sometimes as an add-on treatment for high blood pressure.
What is Doxazosin?
Doxazosin is an alpha-blocker. Its main use is to ease the urinary symptoms of an enlarged prostate, such as a weak stream, hesitancy and frequent urination, and it is sometimes used to help lower blood pressure.
Education and reference only. This is a plain-language guide to Doxazosin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Doxazosin is an alpha-blocker. Its main use is to ease the urinary symptoms of an enlarged prostate (benign prostatic hyperplasia) — such as a weak stream, hesitancy and getting up at night — by relaxing muscle in the prostate and bladder neck. It is also sometimes used as an add-on treatment for high blood pressure that other medicines have not fully controlled. It comes in immediate-release and slow-release (Cardura XL) forms, which behave differently. It is a long-term, once-daily tablet.
How it works
Doxazosin blocks "alpha" receptors that, when active, keep certain muscles tightened. In the prostate and bladder neck, relaxing this muscle eases the flow of urine and reduces prostate-related symptoms. In blood-vessel walls, the same relaxing effect widens the vessels and lowers blood pressure. Because it relaxes vessels, it can cause a drop in blood pressure — particularly with the first dose — which is the main thing to be aware of when starting it.
Company & origin
Originated / developed by: Pfizer.
Doxazosin, an alpha-1 blocker, was developed by Pfizer (USA) and first approved by the US FDA in 1990, marketed as Cardura.
What it treats
Conditions Doxazosin is used for
Practical use
How to take Doxazosin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- The first dose can cause sudden dizziness or fainting, so it is often taken at bedtime when starting.
- Stand up slowly from sitting or lying down, especially in the first few days.
- Can be taken with or without food, at a regular time each day.
- Keep taking it as prescribed, as the benefit on urinary symptoms builds over time.
- Tell your doctor if you feel persistently dizzy or lightheaded.
- If you are due eye surgery for cataracts, tell your eye surgeon you take this medicine.
Weighing it up
Advantages & disadvantages of Doxazosin
Advantages
- Eases bothersome urinary symptoms of an enlarged prostate.
- Taken once daily.
- Can also help lower blood pressure, which may be useful if both conditions are present.
Disadvantages
- Can cause first-dose dizziness or fainting, particularly when standing up.
- May cause headache, tiredness or stuffy nose.
- Does not shrink the prostate, so it treats symptoms rather than the underlying enlargement.
- Can complicate cataract surgery if the surgeon is not told in advance.
Practical use
Good to know
The most important practical point is the "first-dose effect": the first dose (and dose increases) can cause a sharp drop in blood pressure with dizziness or even fainting, so it is often taken at bedtime to start with, and you should stand up slowly. If you are due cataract or other eye surgery, tell the eye surgeon you take (or have taken) doxazosin, as it can cause "floppy iris" during the operation — this changes how the surgeon plans the procedure. The immediate-release and slow-release (XL) forms are not interchangeable; the XL tablet is swallowed whole.
Who should not take it / use with caution
- People prone to fainting on standing, or with a history of low blood pressure on standing.
- Used with caution in people with certain heart conditions and in those having eye (cataract) surgery — the surgeon should be told.
- Care alongside other blood-pressure-lowering medicines and medicines for erectile dysfunction, which together can drop blood pressure too far.
Monitoring
- Blood pressure (lying and standing, especially at the start)
- Urinary symptoms and response
- For dizziness or fainting; a reminder to inform eye surgeons
Side effects
- Dizziness or light-headedness, especially on standing or with the first dose, and tiredness.
- Headache, ankle swelling, a blocked nose, or palpitations.
- Rarely, fainting, or a prolonged painful erection (priapism) — seek urgent advice for the latter; report fainting.
Key interactions
- Other blood-pressure-lowering medicines add to its effect and can cause dizziness or fainting.
- Medicines for erectile dysfunction can lower blood pressure further when combined with it.
- Some medicines can raise its levels — have new medicines checked, especially around starting.
Available as: Tablets, in immediate-release and slow-release (modified-release, "XL") forms that are not interchangeable.
Answers
Doxazosin: frequently asked questions
Why is the first dose of doxazosin taken at bedtime?
The first dose (and any increase) can cause a sudden drop in blood pressure with dizziness or even fainting — the "first-dose effect". Taking it at bedtime means you are lying down if this happens. When you do get up, stand slowly. This effect usually settles as your body adjusts.
I am having cataract surgery — does doxazosin matter?
Yes — tell your eye surgeon that you take, or have ever taken, doxazosin. Alpha-blockers can cause "floppy iris syndrome" during cataract and some other eye operations, which makes surgery trickier. Knowing in advance lets the surgeon plan for it, so do not stop the medicine yourself but do mention it.
What is the difference between Cardura and Cardura XL?
Cardura is the immediate-release form and Cardura XL is a slow-release form that releases the medicine gradually over the day. They are not interchangeable dose-for-dose, and the XL tablet is swallowed whole. Always take the exact form you were prescribed and check with your pharmacist if your tablets look different.
Does doxazosin treat the prostate, blood pressure, or both?
It can do both. Its main use is easing the urinary symptoms of an enlarged prostate by relaxing muscle there, but the same relaxing effect on blood vessels means it is also sometimes used as an add-on for high blood pressure. Your prescriber can tell you which use applies to you.
What is the difference between doxazosin and Cardura?
They are the same medicine — doxazosin is the generic (active-ingredient) name and Cardura (and Cardura XL) are brand names. Generic doxazosin contains the identical active ingredient.
The wider class
About Alpha-blockers
Doxazosin belongs to the alpha-blockers class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Doxazosin.
- electronic Medicines Compendium (SmPC): Cardura / Cardura XL.
- NICE CKS: Doxazosin.
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