How does this medication work? What will it do for me?

Doxazosin belongs to the family of medications called antihypertensives, specifically the alpha-1 receptor antagonists (alpha blockers). It is used to treat mild to moderate high blood pressure. It may be used alone or in combination with other medications that treat high blood pressure. It works to control blood pressure by relaxing blood vessels.

It is also used to treat the symptoms of benign prostatic hyperplasia (BPH or enlarged prostate). It works to relax the muscles around the neck of the bladder, allowing urine to flow out more freely. You may notice an improvement in symptoms within 1 to 2 weeks.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

This medication is available as 1 mg, 2 mg, and 4 mg tablets.

How should I use this medication?

High blood pressure: The recommended adult dose of doxazosin ranges from 1 mg to 16 mg daily, depending on the needs and circumstances of the person. The recommended initial dose of doxazosin for blood pressure is 1 mg once daily. This dose can be doubled every 1 to 2 weeks to a maximum of 16 mg once daily.

BPH: The recommended dose for symptoms of enlarged prostate ranges from 1 mg to 8 mg once daily, depending on the needs and circumstances of the person. The recommended initial dose of doxazosin for BPH is 1 mg once daily. This dose can be doubled every 1 to 2 weeks to a maximum of 8 mg once daily.

Doxazosin can be taken with or without food.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take this medication if you are allergic to doxazosin, quinazolines or any ingredients of the medication.

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • constipation
  • decreased frequency or amount of urine
  • dizziness
  • dry mouth
  • ejaculation problems
  • gas
  • general body pain
  • headache
  • inability to sleep
  • indigestion
  • muscle cramps
  • nausea
  • nervousness, restlessness, unusual irritability
  • runny nose
  • sleepiness or drowsiness
  • sweating
  • unusual tiredness or weakness

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • abdominal pain
  • anxiety
  • depression
  • dizziness or lightheadedness (e.g., when rising from a lying or sitting position)
  • fainting (sudden)
  • muscle twitching
  • shortness of breath
  • swelling of feet or lower legs
  • vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • painful or prolonged erection of the penis (priapism) – although extremely rare, this condition requires immediate medical attention
  • chest pain
  • rapid, pounding, or irregular heart beat
  • symptoms of a severe allergic reaction (e.g., rash; hives; difficulty breathing; swelling of the mouth, tongue, face, or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Blood cell counts: This medication may cause leukopenia (low white blood cell count), which can mean your immune system is weak. If you develop a fever, talk to your doctor as soon as possible. Your doctor will also perform blood tests regularly to monitor your blood cell counts.

BPH: Doxazosin therapy does not cure or change the natural course of benign prostatic hyperplasia (BPH or enlarged prostate). It does not slow down or stop the progression of BPH. Note that BPH is not the same thing as prostate cancer, although they do cause many of the same symptoms. It is possible for men to have both BPH and prostate cancer at the same time.

Your doctor may check for prostate cancer before starting doxazosin and once a year after you turn 50 years old (40 years old if you have a family member who has had prostate cancer).

Drowsiness/reduced alertness: Due to the possibility of excessive lowering of blood pressure, people taking doxazosin should avoid driving or performing hazardous tasks for 24 hours after the first dose, after the dose is increased, and when the medication is started again after not taking it for a period of time. They should also avoid situations where injury could result from loss of consciousness.

Liver and kidney: If you have reduced liver function, are taking medications that reduce liver metabolism, or have reduced kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Low blood pressure: The first or first few doses of doxazosin can cause a marked lowering of blood pressure, especially when moving from a sitting or lying position to a standing position, and may even result in a loss of consciousness. A similar effect can occur if therapy is started again after stopping for more than a few doses. These effects are most likely to occur 2 to 6 hours after taking the medication.

While loss of consciousness due to excessive blood pressure lowering is the most severe side effect of doxazosin, other symptoms of low blood pressure such as dizziness, lightheadedness, or loss of sense of balance can occur.

Lie down when symptoms of low blood pressure occur and be careful when getting up from a lying position (move slowly). If dizziness, lightheadedness, or palpitations are bothersome, report them to your doctor so that dose adjustment can be considered.

The likelihood of excessive lowering of blood pressure can be reduced by the doctor limiting the initial dose of doxazosin to 1 mg, by increasing the dosage slowly, and by starting any other blood pressure medication as directed by your doctor.

Long-term use: Long-term safety and efficacy (i.e., for more than 4 years) have not yet been established for the use of doxazosin in the treatment of BPH.

PDE-5 inhibitors: If you are taking a PDE-5 inhibitor (e.g., sildenafil, tadalafil, or vardenafil) while taking this medication, you may be at risk for low blood pressure. Talk to your doctor.

Pregnancy: There are no studies on the effect of using this medication during pregnancy. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if this medication passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding. In general, women should not breast-feed while taking this medication.

Children: The safety and effectiveness of using this medication have not been established for children. It is not recommended for use by children.

Seniors: Seniors may experience excessive lowering of blood pressure or dizziness when they take doxazosin. Talk to your doctor if you have any concerns.

What other drugs could interact with this medication?

There may be an interaction between doxazosin and any of the following:

  • other medications that reduce blood pressure (e.g., thiazide diuretics, beta-blockers, other alpha-blockers)
  • PDE-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
  • rituximab

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.