Skip to main content


Generic name: tamsulosintam-soo-LOE-sin ]
Drug class: Alpha blockers

Medically reviewed by Philip Thornton, DipPharm. Last updated on Apr 5, 2023.

What is Flomax?

Flomax (tamsulosin) belongs to in a class of medications called alpha blockers. It works by relaxing the muscles in the prostate and bladder so that urine can flow easily.

Flomax capsules are used in men to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia or BPH) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency.

Flomax capsules are not approved for use in women or children.


You should not use Flomax if you are allergic to tamsulosin. Do not take tamsulosin with other similar medicines such as alfuzosin (Uroxatral), doxazosin (Cardura), prazosin (Minipress), silodosin (Rapaflo), or terazosin (Hytrin).

Flomax may cause dizziness or fainting, especially when you first start taking it or when you start taking it again. Be careful if you drive or do anything that requires you to be alert. Avoid standing for long periods of time or becoming overheated during exercise and in hot weather. Avoid getting up too fast from a sitting or lying position, or you may feel dizzy.

If you stop taking this medicine for any reason, call your doctor before you start taking it again. You may need a dose adjustment.

Tamsulosin can affect your pupils during cataract surgery. Tell your eye surgeon ahead of time that you are using this medication. Do not stop using Flomax before surgery unless your surgeon tells you to.

There are many other drugs that can interact with this medicine. Tell your doctor about all medications you use.

Follow all directions on your medicine label and package. Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

Before taking this medicine

You should not use Flomax if you are allergic to tamsulosin.

To make sure this medicine is safe for you, tell your doctor if you have ever had:

Tamsulosin can affect your pupils. If you have cataract surgery, tell the surgeon you use this medicine.

Ask your doctor about prostate cancer screening before and while taking this medicine.

Flomax capsules are not approved for use in women.

How should I take Flomax?

Take Flomax capsules exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Flomax capsules are usually taken once a day, within 30 minutes after the same meal each day.

Swallow the capsule whole and do not crush, chew, break, or open it.

Your blood pressure will need to be checked often.

If you stop using this medicine, do not start it again without your doctor's advice.

Store tightly closed at room temperature, away from moisture and heat.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

If you stop using this medicine for several days in a row, do not start it again without your doctor's advice.

Dosing information

Usual Adult Dose for Benign Prostatic Hyperplasia:

0.4 mg orally once a day; the dose may be increased to 0.8 mg orally once a day in patients who fail to respond to 0.4 mg once a day within 2 to 4 weeks

-This drug should be administered approximately one-half hour following the same meal each day.

Use: Benign prostatic hyperplasia (BPH)

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking Flomax?

Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.

Avoid getting up too fast from a sitting or lying position, or you may feel dizzy.

Flomax side effects

Get emergency medical help if you have signs of an allergic reaction to Flomax (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Tamsulosin may lower your blood pressure and may cause dizziness or fainting, especially when you first start taking it or your dose changes.

Tamsulosin may cause serious side effects. Stop using Flomax and call your doctor at once if you have:

Common Flomax side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Flomax?

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your blood levels of other drugs you use, which may increase side effects or make the medicines less effective.

Tell your doctor about all your current medicines. Many drugs can affect tamsulosin, especially:

This list is not complete and many Other drugs may interact with tamsulosin. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Popular FAQ

Taking Flomax should cause you to more completely empty the bladder each time you pee. This results in fewer trips to the bathroom. Flomax decreases the symptoms of BPH, which include:

  • Starting and stopping the stream of urine
  • Dribbling after urination
  • A sudden strong need to urinate
  • Frequent urination
  • The sensation that the bladder is not empty after urination
  • Having trouble passing urine despite pushing and straining
  • Waking up at night to urinate

Flomax reaches its peak 4 to 5 hours after taking a dose on an empty stomach. The peak occurs 7 to 8 hours after taking a dose with food. It may take up to 5 days to see an effect on urine flow.

Although it is not FDA-approved for this use, Flomax may be used to treat kidney stones. The American Academy of Family Physicians recommends the use of alpha blockers, such as Flomax, to treat kidney stones in some cases. It’s been shown to help:

  • Pass a stone that is larger than 5 millimeters
  • Decrease the time it takes to pass a stone
  • Reduce the need to go to the hospital

It depends on whether or not you have symptoms of BPH after TURP (transurethral resection of the prostate). Your doctor may tell you to continue Flomax while the catheter is in place to aid with emptying your bladder. Depending on symptoms, you may need to continue taking Flomax long-term.

Flomax may lower blood pressure when changing positions. This can happen when moving from a sitting position to a standing position. Flomax more specifically targets the receptors on the prostate than the receptors on blood vessels. Be sure to let your doctor know if you are taking other drugs for high blood pressure.

Flomax is usually taken long-term. If your doctor prescribes it and it is working for you, you will likely continue taking it forever. Your doctor will continue to monitor your symptoms of BPH. It’s important to keep all of your follow-up appointments.

Flomax should be taken at the same time each day, about 30 minutes after a meal, such as dinner.

Flomax can cause a drop in blood pressure when moving from sitting to standing. Symptoms may include feeling dizzy, lightheaded or fainting. If you have these symptoms, you may wish to take your dose at bedtime. If Flomax doesn’t cause these problems for you, you may take it in the morning.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Flomax only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.