What Is Tamsulosin and How Does It Work?

Tamsulosin is used by men to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia-BPH). It does not shrink the prostate, but it works by relaxing the muscles in the prostate and the bladder. This helps to relieve symptoms of BPH such as difficulty in beginning the flow of urine, a weak stream, and the need to urinate often or urgently (including during the middle of the night).

  • Tamsulosin belongs to a class of drugs known as alpha-blockers.
  • Do not use this medication to treat high blood pressure.
  • Tamsulosin is available under the following different brand names: Flomax.

What Are Dosages of Tamsulosin?

Dosage of Tamsulosin:

Dosage Forms and Strengths


  • 0.4mg

Dosing Considerations – Should be Given as Follows:

Benign Prostatic Hypertrophy

0.4 mg orally once daily, 30 minutes after the same meal each day; if the response is inadequate after 2-4 weeks, maybe increased to 0.8 mg once daily; if therapy is interrupted, should be resumed at 0.4 mg once daily

Bladder Outlet Obstruction

Relief of symptoms

  • 0.4 mg orally once daily

Ureteral Stones

Facilitation of stone expulsion

  • 0.4 mg orally once daily; discontinued after successful expulsion (average, 1-2 weeks)

Dosing Modifications

Renal impairment

  • CrCl 10 mL/min or greater: Dosage adjustment not necessary
  • CrCl less than 10 mL/min: Not studied

Hepatic impairment

  • Mild to moderate: Dosage adjustment not necessary
  • Severe: Not studied

Pediatric: Safety and efficacy not established

What Are Side Effects Associated with Using Tamsulosin?

Common Side effects of Tamsulosin include:

  • Headache
  • Dizziness upon standing
  • Runny and stuffy nose
  • Abnormal ejaculation
  • Dizziness
  • Joint pain
  • Infection
  • Weakness and lack of energy
  • Back pain
  • Skin rash
  • Sore throat
  • Diarrhea
  • Muscle pain
  • Chest pain
  • Cough
  • Sleepiness
  • Nausea
  • Sinus infection (sinusitis)
  • Abdominal discomfort
  • Bitter taste
  • Decreased sex drive
  • Insomnia

Postmarketing side effects of tamsulosin reported include:

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Tamsulosin?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

Severe Interactions of tamsulosin include:

  • boceprevir
  • ombitasvir/paritaprevir/ritonavir
  • ombitasvir/paritaprevir/ritonavir and dasabuvir

Tamsulosin has serious interactions with at least 31 different drugs.

Tamsulosin has moderate interactions with at least 73 different drugs.

Mild interactions of tamsulosin include:

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns or for more information about this medicine.

What Are Warnings and Precautions for Tamsulosin?


  • This medication contains tamsulosin. Do not take Flomax if you are allergic to tamsulosin or any ingredients contained in this drug
  • Keep out of reach of children
  • In case of overdose, get medical help or contact a Poison Control Center immediately


  • Hypersensitivity

Effects of Drug Abuse

  • No information available

Short-Term Effects

  • May cause lightheadedness and/or fainting (first-dose effect)
  • See "What Are Side Effects Associated with Using Tamsulosin?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Tamsulosin?"


Pregnancy and Lactation

  • Tamsulosin may be acceptable for use during pregnancy
  • Either animal studies show no risk but human studies are not available, or animal studies showed minor risks and human studies were done and showed no risk
  • Women are unlikely to use tamsulosin, so there is no information on use while breastfeeding
  • Consult your doctor
Medscape. Tamsulosin.

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