Doxazosin is in a group of drugs called alpha-adrenergic blockers. Doxazosin causes the blood vessels (veins and arteries) to relax and expand, improving blood flow. Doxazosin also relaxes muscles in the prostate and bladder neck, making it easier to urinate.

Doxazosin is used to treat hypertension (high blood pressure) and benign prostatic hyperplasia (enlarged prostate).

Doxazosin may also be used for other purposes not listed in this medication guide.

What is the most important information I should know about Doxazosin?

You should not use this medication if you are allergic to doxazosin or similar medicines such as prazosin (Minipress), tamsulosin (Flomax), or terazosin (Hytrin). Doxazosin lowers blood pressure and may cause dizziness or fainting, especially when you first start taking it, or when you start taking it again. To avoid falling, take the first dose of doxazosin at bedtime. You may wish to continue taking this medication only at bedtime if it causes you to feel light-headed.

You may feel very dizzy when you first wake up. Be careful when standing or sitting up from a lying position.

If you stopped taking doxazosin for any reason and have started taking it again, you may feel especially dizzy or light-headed after your first few doses.

Doxazosin can affect the pupils of your eyes during cataract surgery. If you have cataract surgery during your treatment with doxazosin, tell the surgeon ahead of time that you take doxazosin. Do not stop using the medication before surgery unless your surgeon tells you to.

What should I discuss with my doctor before taking Doxazosin?

You should not use this medication if you are allergic to doxazosin or similar medicines such as prazosin (Minipress), tamsulosin (Flomax), or terazosin (Hytrin). If you have liver disease or a history of prostate cancer, you may need a dose adjustment or special tests to safely take doxazosin.

Doxazosin can affect the pupils of your eyes during cataract surgery. If you have cataract surgery during your treatment with doxazosin, tell the surgeon ahead of time that you take doxazosin. Do not stop using the medication before surgery unless your surgeon tells you to.

FDA pregnancy category C. It is not known whether this medication is harmful to an unborn baby. Before taking doxazosin, tell your doctor if you are pregnant or plan to become pregnant during treatment. It is not known whether doxazosin passes into breast milk or if it could harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.

How should I take Doxazosin?

Take this medication exactly as it was prescribed for you. Do not take the medication in larger amounts, or take it for longer than recommended by your doctor. Follow the instructions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results from this medication.

Take each dose with a full glass of water. Doxazosin lowers blood pressure and may cause dizziness or fainting, especially when you first start taking it, or when you start taking it again. To avoid falling, take the first dose of doxazosin at bedtime. You may wish to continue taking this medication only at bedtime if it causes you to feel light-headed.

You may feel very dizzy when you first wake up. Be careful when standing or sitting up from a lying position.

If you stopped taking doxazosin for any reason and have started taking it again, you may feel especially dizzy or light-headed after your first few doses.

To be sure this medication is helping your condition, your blood pressure or prostate will need to be checked on a regular basis. It is important that you not miss any scheduled visits to your doctor.

If you are being treated for high blood pressure, keep using this medication even if you feel fine. High blood pressure often has no symptoms.

Store doxazosin at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at the next regularly scheduled time. Do not take extra medicine to make up the missed dose.

If you miss doses for several days in a row, call your doctor before taking any additional doses. You may need to use a lower dose of doxazosin for a short time.

What happens if I overdose?

Seek emergency medical attention if you think you have used too much of this medicine.

Overdose symptoms may include drowsiness, fainting, or seizure (convulsions).

Doxazosin side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects:

• fast or pounding heartbeats;
• feeling light-headed, fainting;
• swelling in your hands, ankles, or feet; or
• penis erection that is painful or lasts 4 hours or longer.

Less serious side effects may include:

• weakness;
• headache;
• dizziness; or
• diarrhea, stomach pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Doxazosin Dosing Information

Usual Adult Dose for Hypertension:

Initial dose: 1 mg orally once a day.
Maintenance dose: 1 to 16 mg orally once a day.

Usual Adult Dose for Benign Prostatic Hyperplasia:

Initial dose:
Immediate-release: 1 mg orally once a day.
Extended-release: 4 mg orally once a day with breakfast

Maintenance dose:
Immediate-release: 1 to 8 mg orally once a day.
Extended-release: 4 to 8 mg orally once a day with breakfast. Depending on the patient’s symptomatic response and tolerability, the dose may be increased to 8 mg (the maximum recommended dose). The recommended titration interval is 3 to 4 weeks.

If switching from immediate-release doxazosin to doxazosin extended-release tablets, therapy should be initiated with the lowest dose (4 mg once daily). Prior to starting therapy with doxazosin extended-release tablets, the final evening dose of immediate-release doxazosin should not be taken. If doxazosin extended-release is discontinued for several days, therapy should be restarted using the 4 mg once daily dose.

Usual Geriatric Dose for Hypertension:

Initial dose: 0.5 mg orally once a day.

What other drugs will affect Doxazosin?

Before using doxazosin, tell your doctor if you regularly use other medicines that make you sleepy (such as cold or allergy medicine, sedatives, narcotic pain medicine, sleeping pills, muscle relaxers, and medicine for seizures, depression, or anxiety). They can add to sleepiness caused by doxazosin.

Tell your doctor about all other medications you use, especially:

• sildenafil (Viagra, Revatio)
• tadalafil (Cialis); or
• vardenafil (Levitra).

This list is not complete and there may be other drugs that can interact with doxazosin. Tell your doctor about all your prescription and over-the-counter medications, vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start a new medication without telling your doctor.

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