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.

High blood pressure: The recommended adult dose of doxazosin ranges from 1 mg to 16 mg daily, depending on the person's needs and circumstances. The recommended initial dose of doxazosin for blood pressure is 1 mg once daily. This dose can be slowly increased 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 person's needs and circumstances. 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. If you miss taking the medication for several days in a row, contact your doctor for advice. You may need to restart on a lower dose and gradually increase again.

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

1 mg
Each white-to-off-white, capsular-shaped tablet, debossed "1 mg" with break line on one side and "R" on the other, contains doxazosin mesylate equivalent to 1 mg of doxazosin. Nonmedicinal ingredients: colloidal silicone dioxide, lactose monohydrate, magnesium stearate, microcrystalline cellulose PH, pregelatinized starch, sodium lauryl sulfate, and sodium starch glycolate Type A.

2 mg
Each pale-pink-to-pink, capsular-shaped tablet, debossed "2 mg" with break line on one side and "R" on the other, contains doxazosin mesylate equivalent to 2 mg of doxazosin. Nonmedicinal ingredients: FD&C Red No. 40 Alum Lake, colloidal silicone dioxide, lactose monohydrate, magnesium stearate, microcrystalline cellulose PH, pregelatinized starch, sodium lauryl sulfate, and sodium starch glycolate Type A.

4 mg
Each pale-pink-to-pink, capsular-shaped tablet, debossed "4 mg" with break line on one side and "R" on the other, contains doxazosin mesylate equivalent to 4 mg of doxazosin. Nonmedicinal ingredients: FD&C Red No. 40 Alum Lake, colloidal silicone dioxide, lactose monohydrate, magnesium stearate, microcrystalline cellulose PH, pregelatinized starch, sodium lauryl sulfate, and sodium starch glycolate Type A.

Do not take this medication if you:

• are allergic to doxazosin or any ingredients of the medication
• are allergic to other quinazolines, such as alfuzosin or prazosin
• have hereditary problems of galactose intolerance, the Lapp lactase deficiency, or glucose-galactose malabsorption

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.

• dizziness
• ejaculation problems
• headache
• sleepiness or drowsiness
• unusual tiredness or weakness
• weight gain

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:

• dizziness or lightheadedness (e.g., when rising from a lying or sitting position)
• fainting (sudden)
• increased frequency of infections (e.g., sore throat, fever, feeling unwell, cough, sinus or chest congestion)
• shortness of breath
• swelling of feet or lower legs

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 heartbeat
• 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.

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 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, avoid driving or performing hazardous tasks for 24 hours after your first dose of doxazosin, after the dose is increased, and when the medication is started again after not taking it for a period of time. You should also avoid situations where you could be injured if you were to lose consciousness.

Eye problems: During eye surgery for cataracts, people who take or have taken doxazosin are at risk for developing a condition called intraoperative floppy iris syndrome (IFIS). This condition can lead to eye damage. If you are planning to have an operation on your eye, inform your doctor if you are taking or have taken doxazosin.

Kidney function: If you have reduced kidney function or kidney disease, 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.

Lactose: This medication contains lactose. If you have hereditary problems of galactose intolerance, lactase deficiency or glucose-galactose malabsorption, discuss with your doctor whether this medication is appropriate for you.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, 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.

People taking doxazosin may have changes in liver function that produce abnormal liver test results. Your doctor will recommend regular liver tests while you are taking this medication. If you have severe changes in liver function, your doctor may recommend that you take a lower dose of this medication or stop taking it altogether.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Low blood pressure: The first dose or first few doses of doxazosin can cause your blood pressure to lower. You may notice this particularly when moving from a sitting or lying position to a standing position. Be alert for any lightheadedness or dizziness. A similar effect can occur if doxazosin 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.

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.

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: Doxazosin crosses the placenta and may affect the developing baby if it is taken 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: This medication passes into breast milk. If you are breast-feeding and taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

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.

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

• aldesleukin
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• antipsychotics (e.g., clozapine, olanzapine, quetiapine, risperidone)
• "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
• barbiturates (e.g., butalbital, phenobarbital)
• bortezomib
• bosentan
• brimonidine
• bromocriptine
• clarithromycin
• clomipramine
• cobicistat
• decongestant cold medications (e.g., ephedrine, phenylephrine, pseudoephedrine)
• decongestant eye drops and nasal sprays (e.g., naphazoline, oxymetazoline, xylometazoline)
• diazoxide
• diuretics (water pills; e.g., bumetanide, furosemide)
• duloxetine
• epinephrine
• flunarizine
• general anesthetics (medications used to put people to sleep before surgery)
• HIV protease inhibitors (e.g., atazanavir, darunavir, lopinavir, ritonavir)
• imipramine
• levodopa
• methylphenidate
• mifepristone
• monoamine oxidase inhibitors (e.g., phenelzine, rasagiline, selegiline, tranylcypromine)
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• obinutuzumab
• other alpha blockers (e.g., alfuzosin, prazosin, tamsulosin)
• pentoxifylline
• phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• primidone
• protein kinase inhibitors (e.g., brigatinib, ceritinib, idelalisib, tucatinib)
• riociguat
• ropinirole
• rotigotine
• sacubitril
• sotalol
• tretinoin
• yohimbine

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.