Cardura

Introduction

Written by Lee Holland, PharmD, MPH
Medically reviewed by Victor Nguyen, PharmD, MBA 
Updated on November 3, 2023

Doxazosin (doks AY zoe sin) is a generic medication prescribed for high blood pressure and enlarged prostate. Doxazosin belongs to a group of drugs called quinazolines.

Side effects of doxazosin

Doxazosin may cause mild or serious side effects. More common mild side effects of doxazosin and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about doxazosin’s side effects, see this article or ask your doctor or pharmacist. You can also refer to the prescribing information for doxazosin listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of doxazosin are listed below. These side effects may differ based on the form of doxazosin you take.

This article doesn’t include all possible mild side effects of the drug. To learn more about doxazosin’s side effects based on the form, refer to the prescribing information for doxazosin listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Doxazosin oral tablet’s mild side effects include:

• general discomfort
• fatigue (low energy)
• low blood pressure
• dizziness
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for doxazosin” section.

Serious side effects

Serious side effects of doxazosin are listed below. These side effects may differ based on the form of doxazosin you take.

This article doesn’t include all possible serious side effects of the drug. To learn more about doxazosin’s side effects based on the form, refer to the prescribing information for doxazosin listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, doxazosin’s serious side effects include: 

• low blood pressure when standing up, which can cause you to feel dizzy or lightheaded
• cataract surgery complications
• prolonged erection
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for doxazosin” section.

Uses of doxazosin

The Food and Drug Administration (FDA) approves prescription drugs such as doxazosin for certain conditions. Approved uses for doxazosin are described below.

Use for enlarged prostate

Doctors may prescribe doxazosin tablets for treating benign prostate hyperplasia, also known as an enlarged prostate. It’s used for this purpose in adults. It’s usually prescribed as a long-term treatment.

The prostate is a gland found in males.* It’s found under the bladder and surrounds the urethra. The urethra is the tube that carries urine from the bladder to the outside of the body. When the prostate grows, it can narrow the urethra. If not treated, this can cause difficulty urinating and other urinary tract and kidney problems.

* Sex and gender exist on spectrums. In this article, we use the term male to refer to a person’s sex assigned at birth.

Use for high blood pressure

Doctors may prescribe doxazosin tablets for treating high blood pressure. It’s used for this purpose in adults. It’s usually prescribed as a long-term treatment.

People with high blood pressure usually don’t have any symptoms. But high blood pressure can damage your internal organs and eyes if left untreated. Some complications from high blood pressure include heart attack and stroke. Medications like doxazosin can lower blood pressure and prevent internal damage and complications.

Doctors often prescribe doxazosin along with other high blood pressure medications.

Common questions about doxazosin

Below you’ll find answers to a few commonly asked questions about doxazosin.

How does doxazosin work?

Doxazosin works by relaxing muscles and blood vessels. This is known as its mechanism of action.

For enlarged prostate, doxazosin helps relax the muscles around the prostate gland, allowing urine to flow more easily.

For high blood pressure, doxazosin helps relax blood vessels. This can slightly increase the size of blood vessels and lower blood pressure.

If you’d like to know more about how doxazosin works, talk with your doctor or pharmacist.

How long does doxazosin take to start working?

For an enlarged prostate, doxazosin can start working in about a week. You will notice that it’s easier to urinate. Other symptoms may also improve.

For high blood pressure, doxazosin starts working between 1 and 6 hours after the first dose. You may not notice any benefits since high blood pressure may not have symptoms associated with it. But lowering your blood pressure can lower your risk of heart attack and stroke.

For more information on how long doxazosin takes to start working, talk with your doctor or pharmacist.

Interactions and warnings for doxazosin

Below you’ll find information about doxazosin’s possible interactions and warnings.

Interactions of doxazosin

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take doxazosin, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs 
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for doxazosin” section below.

Warnings for doxazosin

Some people should not take doxazosin, and others should take it cautiously.

Doxazosin could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether doxazosin is a safe option for you. These warnings may differ based on the form of doxazosin you take.

Ask your doctor about specific warnings for doxazosin, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Doxazosin can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to doxazosin or any of its ingredients, your doctor will likely recommend that you do not take doxazosin. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to doxazosin, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of doxazosin

If you take doxazosin by mouth, you should not take more doxazosin than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much doxazosin, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and doxazosin

Information about doxazosin and pregnancy and breastfeeding is described below.

Doxazosin and pregnancy

It’s not known whether doxazosin should be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.

Doxazosin and breastfeeding

It’s not known whether doxazosin should be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.

What to ask your doctor

Let your doctor know if you have questions about doxazosin or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• What are my options if I can’t afford my medication?
• Will my doctor need to change my dosage of doxazosin if I am taking other medications?
• Am I at higher risk of side effects than others?

Resources

• Doxazosin — doxazosin tablet (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/2ea9bb6b-a4f0-496a-b27b-4454167a4b70/spl-doc
• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.