What is Tamsulosin: Uses, Warnings & Interactions

Updated Aug 19, 2025  •  Published Dec 30, 2020

Tamsulosin is a generic prescription drug that relieves urination retention in men with an enlarged prostate. As an alpha blocker, tamsulosin relaxes the smooth muscle cells in the prostate and bladder neck, allowing patients to more completely empty the bladder when urinating. Doses are taken once daily, one-half hour following the same meal each day.

Tamsulosin overview

BRAND NAMES:

  • Flomax

Generic Names:

  • Tamsulosin HCl

Uses:

  • Treats the urinary symptoms of benign prostatic hyperplasia (enlarged prostate).

Therapeutic Classes:

  • Alpha blocker

Forms:

  • Capsule

How it’s taken:

  • By mouth

What is Tamsulosin used for?

Tamsulosin is FDA-approved to treat men with urinary retention caused by an enlarged prostate. Doctors sometimes use it off-label to treat urinary retention in women or to help patients pass kidney stones.

What form(s) does Tamsulosin come in

  • Capsule

    • 0.4 mg

What are common Tamsulosin doses?

  • For the urinary symptoms of benign prostatic hyperplasia (enlarged prostate): 0.4–0.8 mg taken once per day, ½ hour after the same meal each day

Common Tamsulosin prescriptions

  • Tamsulosin HCl
    0.4mg capsule

How to take Tamsulosin

  • Follow all the prescriber’s instructions. 

  • Please read the Patient Information sheet before taking this medicine.

  • Take only one dose daily.

  • Take each dose 30 minutes after the same meal each day. 

    • For instance, if you take the first dose after breakfast, take all other daily doses after breakfast.

  • Swallow the capsule whole. Do not crush, chew, or open it.

  • Store tamsulosin capsules at room temperature.

What to do if you miss a dose of Tamsulosin

  • If you miss a dose, take it as soon as you remember.

  • If it’s the next day, skip the missed dose. Take the next dose when you usually would.

  • If several doses in a row are missed, call the prescriber for advice before taking another dose.

  • Do not take extra medicine to make up for a missed dose.

Tamsulosin contraindications

  • This medicine is not right for everyone. 

  • Do not use it if you have had an allergic reaction to tamsulosin.

Tamsulosin warnings

  • Inform other healthcare professionals treating you that you are taking tamsulosin.

  • The prescriber needs regular visits to check your progress and the effects of tamsulosin therapy. Keep all appointments.

  • Before starting tamsulosin, make sure the prescriber knows your medical history and current medical problems, particularly:

    • Kidney problems

    • Liver problems

    • A history of low blood pressure

    • Sulfa drug allergies

  • Tell the healthcare provider if you’ve been diagnosed as a poor CYP2D6 metabolizer. This is a genetic condition that affects your ability to break down certain drugs like tamsulosin.

  • Tamsulosin can cause problems during cataract or glaucoma surgery. Tell the ophthalmologist before the procedure that you’re using tamsulosin.

  • Tamsulosin can cause dizziness, lightheadedness, or fainting when standing up or changing position. 

    • To manage this, stand or sit up slowly. 

    • Sit back down if you feel dizzy until the lightheadedness passes.

    • Avoid driving or other potentially hazardous activities until you know how the medicine affects you.

  • In rare cases, tamsulosin can cause persistent, painful erections. Get immediate medical attention when this happens.

Tamsulosin interactions

  • Tell the prescriber about all the drugs and supplements you regularly take. In particular, tamsulosin can cause problems in people taking:

    • Other alpha blockers

    • Erectile dysfunction medications

    • Blood pressure medications

    • HIV/AIDS drugs called protease inhibitors

    • Cimetidine, erythromycin, itraconazole, ketoconazole, paroxetine, terbinafine

  • Tell other healthcare providers you are using tamsulosin before they prescribe new medications.

Tamsulosin side effects

Serious side effects

Talk to a doctor if you notice any signs or symptoms of a possible serious side effect, including:

  • Lightheadedness, dizziness, fainting

  • Painful, prolonged erection of your penis

  • Blistering, peeling, red skin rash

  • Allergic reaction: Itching, skin rash, hives, swelling in your face, mouth, or throat, chest tightness, trouble breathing, trouble swallowing

Less serious side effects

  • Headache

  • Problems with ejaculation

  • Runny or stuffy nose

  • Dizziness

  • Infection

Sources:

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