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Terazosin, Oral ter-AY-zoh-sin

What are other names for this medicine?

Type of medicine: alpha blocker; antihypertensive; treatment for enlarged prostate

Generic and brand names: terazosin, oral

What is this medicine used for?

This medicine is taken by mouth to treat and control high blood pressure. Your healthcare provider may prescribe other medicines to be taken along with this medicine to increase its effectiveness.

This medicine is also used to treat the symptoms of an enlarged prostate gland.

This medicine may be used for other conditions as determined by your healthcare provider.

What should my healthcare provider know before I take this medicine?

Before taking this medicine, tell your healthcare provider if you have ever had:

  • an allergic reaction to any other medicine
  • a heart attack, chest pain, or heart failure
  • liver disease
  • low blood pressure
  • prostate cancer

Tell your healthcare provider if you are taking any other medicines for high blood pressure. Talk to your healthcare provider before you use any nasal decongestants or take cold medicines, including nonprescription products.

Females of childbearing age: Tell your healthcare provider if you are pregnant or plan to become pregnant. It is not known whether this medicine will harm an unborn baby. Do not breast-feed while taking this medicine without your healthcare provider's approval.

How do I take it?

Check the label on the medicine for directions about your specific dose. Take this medicine exactly as directed by your healthcare provider. Do not take more or less or take it longer than prescribed. Do not stop taking this medicine without your healthcare provider's approval, even if you start to feel better.

Take this medicine at bedtime unless your healthcare provider tells you otherwise.

What if I miss a dose?

If you miss a dose, take it as soon as you remember unless it is almost time for the next scheduled dose. In that case, skip the missed dose and take the next one as directed. Do not take double doses. If you are not sure of what to do if you miss a dose, or if you miss more than one dose, contact your healthcare provider.

What if I overdose?

If you or anyone else has intentionally taken too much of this medicine, call 911 or go to the emergency room right away. If you pass out, have seizures, weakness or confusion, or have trouble breathing, call 911. If you think that you or anyone else may have taken too much of this medicine, call the poison control center. Do this even if there are no signs of discomfort or poisoning. The poison control center number is 800-222-1222.

Symptoms of an acute overdose may include: drowsiness, dizziness, fainting.

What should I watch out for?

You may feel dizzy or faint when you get up quickly after sitting or lying down. Getting up slowly may help. If you feel dizzy or faint while you are standing, lie down for a while and then get up slowly.

Alcohol, exercise, and hot weather may make you feel dizzy, lightheaded, or drowsy. Do not drink large amounts of alcohol, and be careful when you exercise in hot weather. Do not drive or operate machinery unless you are fully alert. This is especially important:

  • after you take the first few doses
  • after your dosage is increased
  • when you start taking the medicine again after some time without it.

While you are taking this medicine, do not take medicines to treat erectile dysfunction. Your blood pressure could suddenly drop and you could get dizzy or faint.

Rarely, this medicine may cause a painful erection of the penis that will not return to normal. If this occurs, contact your healthcare provider or get medical care right away. It can lead to permanent erectile dysfunction if not treated.

If you need emergency care, surgery, or dental work, tell the healthcare provider or dentist you are taking this medicine. If you need to have eye surgery at any time during or after taking this medicine, tell your healthcare provider that you are taking or have taken this medicine.

Your healthcare provider will need to see you regularly to check your blood pressure and to adjust your dosage, if necessary. Keep all appointments.

What are the possible side effects?

Along with its needed effects, your medicine may cause some unwanted side effects. Some side effects may be very serious. Some side effects may go away as your body adjusts to the medicine. Tell your healthcare provider if you have any side effects that continue or get worse.

Life-threatening (Report these to your healthcare provider right away. If you cannot reach your healthcare provider right away, get emergency medical care or call 911 for help): Allergic reaction (hives; itching; rash; trouble breathing; tightness in your chest; swelling of your lips, tongue, and throat).

Serious (report these to your healthcare provider right away): Irregular or fast heartbeat; fainting; chest pain; trouble breathing; swelling or numbness in your hands, legs, or feet or any unexplained swelling; severe or constant headache; dizziness; weakness; trouble urinating; painful or prolonged erection.

Other: Nausea, weakness, tiredness, drowsiness, stomach pain, nervousness, headache, vomiting, vision problems, runny nose, stomach pain, diarrhea, constipation, dry mouth, back pain, joint or muscle pain, change in sexual desire or ability.

What products might interact with this medicine?

When you take this medicine with other medicines, it can change the way this or any of the other medicines work. Nonprescription medicines, vitamins, natural remedies, and certain foods may also interact. Using these products together might cause harmful side effects. Talk to your healthcare provider if you are taking:

  • ACE inhibitors such as benazepril (Lotensin), captopril, enalapril (Vasotec), fosinopril, lisinopril (Prinivil, Zestril), quinapril (Accupril), and ramipril (Altace)
  • angiotensin receptor II blockers such as candesartan (Atacand), eprosartan (Teveten), irbesartan (Avapro), losartan (Cozaar), olmesartan (Benicar), telmisartan (Micardis), and valsartan (Diovan)
  • beta blockers such as acebutolol (Sectral), atenolol (Tenormin), carvedilol (Coreg), labetalol (Normodyne, Trandate), metoprolol (Lopressor, Toprol XL), nadolol (Corgard), pindolol, propranolol (Inderal), and sotalol (Betapace)
  • calcium channel blockers such as diltiazem (Cardizem, felodipine, isradipine (DynaCirc CR), nicardipine (Cardene), nifedipine (Adalat CC, Procardia), and verapamil (Calan, Covera-HS, Isoptin SR, Verelan, Tiazac)
  • diuretics (water pills) such as amiloride, bumetanide, chlorothiazide (Diuril), furosemide (Lasix), hydrochlorothiazide (Microzide), spironolactone (Aldactone), torsemide (Demadex), and triamterene (Dyrenium)
  • natural remedies such as dong quai, ephedra, garlic, ginseng, saw palmetto, and yohimbe
  • medicines to treat erectile dysfunction such as sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra)

Do not drink alcohol while you are taking this medicine.

If you are not sure if your medicines might interact, ask your pharmacist or healthcare provider. Keep a list of all your medicines with you. List all the prescription medicines, nonprescription medicines, supplements, natural remedies, and vitamins that you take. Be sure that you tell all healthcare providers who treat you about all the products you are taking.

How should I store this medicine?

Store this medicine at room temperature. Keep the container tightly closed. Protect it from heat, high humidity, and bright light.


This advisory includes selected information only and may not include all side effects of this medicine or interactions with other medicines. Ask your healthcare provider or pharmacist for more information or if you have any questions.

Ask your pharmacist for the best way to dispose of outdated medicine or medicine you have not used. Do not throw medicine in the trash.

Keep all medicines out of the reach of children.

Do not share medicines with other people.


Developed by RelayHealth.
Medication Advisor 2012.1 published by RelayHealth.
Last modified: 2010-12-09
Last reviewed: 2010-09-09
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2012 RelayHealth and/or its affiliates. All rights reserved.
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