Men's Health

What Is Tamsulosin: Usage, Dosage, Side Effects, and Drug Interactions

What Is Tamsulosin: Usage, Dosage, Side Effects, and Drug Interactions

Generic Name: Tamsulosin

Brand Name: Flomax

What is tamsulosin?

Tamsulosin is an alpha-blocker that helps treat the symptoms of benign prostatic hyperplasia (BPH) or an enlarged prostate. This medication works by relaxing the bladder and prostate muscles to help improve the flow of urine in men and relieve the symptoms of BPH, which include:

  • Frequent urination (urgent need to urinate)
  • Nocturia (excessive urination at night)
  • Trouble starting urination
  • Weak urine stream 
  • Dribbling after urination
  • Urinary retention (inability to completely empty the bladder)

Tamsulosin is available under the brand name Flomax. Tamsulosin is not approved for the treatment of high blood pressure. 

What is benign prostatic hyperplasia (BPH)?  

Benign prostatic hyperplasia (BPH) is the non-cancerous enlargement of the prostate gland. As males age, their prostate goes through periods of growth. The first one occurs during adolescence when their prostate doubles in size. Another period of growth happens when men reach the age of 25 and above. As men age, their prostate tends to become larger. BPH usually occurs during the second phase of growth. 

An enlarged prostate tends to squeeze the urethra, disrupting urine flow from the bladder and prevent the urine from being expelled. The bladder wall also becomes thicker and loses its ability to completely empty, leaving some urine in the bladder. 

BPH is not cancer and does not lead to nor cause cancer. However, cancer and BPH can occur at the same time. BPH is commonly seen in the aging male population. Approximately half of all men who are 51-60 years old have BPH and up to 90 percent of those who are 80 years old and older have BPH. 

Important Notes

This medication should not be used if you are allergic to tamsulosin or any of its ingredients. Tamsulosin should not also be used along with the following similar medications:

This medicine may cause fainting or dizziness, particularly during initial treatment or when patients start taking tamsulosin again. For this reason, extra caution must be taken if you drive or perform anything that requires focus and mental alertness. Do not get up too fast from a lying or sitting position to avoid feeling dizzy. 

A dose adjustment may be needed if you stopped taking this medicine for a time, and then need to start taking it again. Consult your doctor before taking this medication for a proper dose adjustment. 

During cataract surgery, this medication can affect the pupils. Make sure to inform your eye surgeon that you are using tamsulosin before undergoing the surgery. Do not stop taking this medication before surgery unless your surgeon specifically says otherwise. 

Many drugs can interact with tamsulosin, so it is very important to inform your healthcare provider of all the medications you use. 


Read and follow the directions indicated on the prescription label. The dose may be occasionally adjusted by your doctor to get the best results. This medication should not be used longer than prescribed and in larger or smaller amounts. 

Take tamsulosin at the same time every day. This medication is usually taken once a day and about half an hour after a meal. Swallow the capsule whole instead of opening, chewing, or crushing the capsule. 

Tamsulosin tends to lower a person's blood pressure, so it may cause fainting or dizziness, particularly at the start of treatment or when starting the medication again. Seek immediate medical help if you experience severe dizziness or feel like you're going to pass out. 

There are also other causes of low blood pressure. They include heart disease, excessive sweating, consuming a diet low in salt, diuretics, vomiting, diarrhea, or dialysis. Inform your healthcare provider if you continue to have vomiting and diarrhea. 

Before and during tamsulosin treatment, you will be checked for prostate cancer. Your blood pressure will also be frequently checked. 

Store this medication in a cool, dry place, and away from heat and moisture. You can ask your healthcare provider or pharmacist if you have more questions about using tamsulosin. 


  • Initial Adult Dose for BPH: 0.4 mg orally taken once a day 
  • Maximum Dose for BPH: 0.8 mg orally taken once a day

If the medicine is discontinued for several days, treatment should start again with 0.4 mg once a day. If you missed a dose, take it as soon as you remember. However, if it is time for your next dose, take only one dose. Do not catch up by taking two doses to avoid serious side effects. 

You can tell if the medicine is working if you notice an improvement in your symptoms, such as the lesser need to urinate often, lesser urinary urgency, and a stronger urine flow. 

Side Effects

The most commonly reported side effects of this medication are:

Seek emergency medical help if you notice any signs and symptoms of an allergic reaction, such as:

  • Hives or rash
  • Itching
  • Difficulty breathing
  • Swelling of the face, throat, tongue, or lips

Stop using this medicine and seek immediate medical attention if you have:

  • Lightheadedness or feeling faint
  • Painful erection that lasts for four hours or longer
  • Severe skin reactions
  • Fever
  • Sore throat
  • Swelling of the face or tongue
  • Burning in your eyes
  • Skin pain followed by a red or purple skin rash that spreads in the face or upper body along with blistering and peeling

Other common side effects of tamsulosin include:

Drug Interactions

The following drugs may interact with tamsulosin:

  • Other alpha-blocker drugs (prazosin, terazosin, doxazosin)
  • Acid-blocking drug (cimetidine)
  • Antibiotic (erythromycin)
  • Antidepressant or SSRI (paroxetine)
  • Azole antifungals (ketoconazole, itraconazole)
  • Terbinafine
  • Drugs for the treatment of pulmonary hypertension or erectile dysfunction (tadalafil, sildenafil, vardenafil)
  • Azole antifungals (ketoconazole, itraconazole)
  • Clarithromycin
  • Boceprevir
  • Cobicistat
  • HIV-protease inhibitors (ritonavir, lopinavir)
  • Ribociclib
  • Alfuzosin

Do not take this drug if you have had an allergic reaction to tamsulosin or sulfa. Taking this drug again could cause fatal consequences or death. Sulfa is found as an ingredient in certain medications. Speak with your doctor if you have had a serious allergic reaction to sulfa.