Tamsulosin (Flomax): Uses, Dosage, Side Effects, and Abuses
January 30, 201901,366


What is Tamsulosin?

Tamsulosin is a α1-adregenic receptor blocker. It is used treat the symptoms of benign prostatic hyperplasia (BPH).1

Tamsulosin is a prescription medication. It cannot be bought over-the-counter.1,2

Tamsulosin is sold under the brand name Flomax.1 It has also been sold under a variety of generic names since 2010.2


How does tamsulosin work in the body?

Tamsulosin works by blocking the activation of specific receptors in the prostate and bladder. These receptors are called α1A-adregenic receptors.1

α1A-receptors are activated by a class of molecules called catecholamines.3

Catecholamines are chemicals that are released by certain nerves when they fire. Some common catecholamines you might know include epinephrine and norepinephrine.3

Normally, catecholamines released from an active nerve bind to α1A receptors on the surface of prostate and bladder muscle cells. The binding of catecholamine tells the cells to contract.1,3

When tamsulosin is present, though, tamsulosin can bind to the α1A receptor instead. This keeps the catecholamines from binding and therefore, the prostate and bladder muscles stay relaxed.1


Figure 1: Diagram of a Nerve Signaling to Prostate Cell.


Nerve cells release catecholamines (pink circles) which bind to α1A-adregenic receptors. Activated α1A– receptors tell the prostate or bladder muscle cell. Tamsulosin prevents catecholamines from binding to the α1A– receptors (red line). Original diagram; see texts for sources.

This is very helpful for men with a condition called benign prostatic hyperplasia (BPH).1


What is Benign Prostatic Hyperplasia?

BPH is a condition characterized by growth of the prostate that is not caused by cancer.4

It is a very common condition among men over the age of 50. In fact, around 90 percent of men in their 80s have BPH.4,5

Doctors are not sure what causes the prostate to start growing in BPH. They think it might be a combination of many factors involved in the aging process. These factors may include5:

  • Changes in nerve function
  • Changes in growth hormone levels
  • Changes in metabolism
  • Development of chronic inflammation in the prostate

Regardless of why the prostate begins to grow, if it gets too big, it can push in on the urethra. When it pushes too much, the urine that normally flows freely during urination cannot flow well anymore. This leads to symptoms of BPH.1,4


Figure 2: Effect of a Normal Prostate vs. Enlarged Prostate on Urine Flow

If the prostate pinches in on the urethra, it can cause urine to become trapped in the bladder (yellow arrows). (


Symptoms of BPH

Symptoms of BPH include4:

  • Difficulty starting the flow of urine
  • Urine flow that stops and starts again
  • Feeling that there is still urine in the bladder after using the restroom
  • Having to urinate often
  • Having to get up at night to empty your bladder

In addition to these frustrating symptoms, long-term inability to empty your bladder can lead to more serious conditions, including4:

  • Bladder infections
  • Decrease in the ability of your kidneys to work
  • Blood in your urine
  • Build-up of toxins in the blood that should normally be filtered into the urine

Though tamsulosin does not reverse the growth of the prostate, it can help ease urine flow by helping the prostate stay relaxed. This helps keep urine from backing-up and decreases the risk of developing more serious symptoms.1,4


Tamsulosin Uses

The only FDA-approved use for tamsulosin is the treatment of BPH symptoms (see above).1

However, doctors sometimes prescribe tamsulosin for other conditions as well. Off-label uses for tamsulosin may include6-12:

  • Easing the passing of kidney stones
  • Reducing pain after ureter stent placement
  • Overactive bladder in women

Tamsulosin and Kidney stones

Kidney stones are a build-up of solid salts in the kidneys. Usually, this salt is calcium oxalate.7

When these stones form in the kidneys, it causes severe pain.7

The ultimate goal for treating kidney stones is to remove the stones from the kidney. One option for doing so is to get the stones to flow out of the kidney with the urine.7

Doctors sometimes prescribe tamsulosin to help with this process.6,7,13

The idea is that tamsulosin will help keep the bladder, urethra, ureter and prostate (in men) relaxed. This should also help keep the organs from spasming around the stone as it moves along. The stone should be able to move more quickly and the process should be less painful.6

However, new studies suggest that these effects may only be helpful in individuals with large stones.6,13

In those with kidney stones larger than 5 mm in diameter, tamsulosin may help the stone pass more quickly and with less pain.6,13

Multiple studies have shown no benefit for those with smaller stones, though.6,13,14


Tamsulosin and Ureter Stent Maintenance

The treatment of some kidney conditions includes the insertion of a ureter stent. The stent is a device that holds the ureter (the tube which connects the kidney to the bladder) open, so that urine can flow freely.10,11

Many individuals receiving a stent report side effects. These include10,11:

  • Frequent urge to urinate
  • Blood in urine
  • Infections
  • Bladder irritation and pain
  • Pain in the side or lower abdomen
  • Anxiety
  • Decreased quality of life

Studies suggest that tamsulosin may help decrease the severity of these symptoms.10,11 Scientists think this is likely due to the medication preventing spasms of the ureter caused by the presence of a foreign object.10

Tamsulosin and Overactive Bladder

Overactive Bladder is a condition characterized by urinary urgency. It is usually accompanied by a frequent need to use the restroom, even at night.9

Overactive Bladder can be caused by a variety of different conditions, including9:

  • A urinary tract infection
  • Impaired bladder contractions
  • Decreased blood flow to the bladder
  • Neurological problems (Alzheimer’s Disease, Parkinson’s Disease, dementia, multiple sclerosis, stroke)

Some individuals experience Overactive Bladder without doctors ever being able to find a cause. This is called idiopathic Overactive Bladder.9

Some studies suggest that tamsulosin may be helpful for improving the symptoms of Overactive Bladder.15,8


Tamsulosin Dosages

Adult Dosage


The recommended initial dose of tamsulosin for adult men with BPH is 0.4 mg per day.1

If your symptoms do not respond well within 2 to 4 weeks, your doctor may increase your dose to 0.8 mg per day.1


Since tamsulosin is not approved to treat any condition in women, there are no recommended dosages for this population.1

Studies looking at whether tamsulosin may be helpful for treating Overactive Bladder in women have used daily doses ranging from 0.2-1.5 mg.12,15 Doses of 0.2 mg per day were found to be effective.15

If your doctor decides to prescribe tamsulosin off-label to treat your Overactive Bladder symptoms, he will individualize your personal dosage.

Elderly Individuals

There is no difference in dosage recommended for older individuals. Elderly men experiencing BPH symptoms may receive 0.4 mg or 0.8 mg per day of tamsulosin, without restrictions.1

Individuals with Kidney and Liver Disease

It is unknown if individuals with end-stage kidney or liver disease should take smaller doses of tamsulosin or not.1

Dosage for Children

Children should not take tamsulosin.1


Tamsulosin Side Effects

Though the α1A-receptor is found concentrated in the prostate, it can also be found in other parts of the body.3

When tamsulosin prevents α1A-receptors in other parts of the body from being activated, it can cause side effects.

Additionally, although tamsulosin appears to preferentially bind to the α1A-receptor, it can also bind to the two other subtypes of α1-receptors: α1B and α1D.1 Blocking signaling for α1B and α1D receptors can also cause side effects.

Some of these side effects are common and relatively mild. Others can be quite serious.

More Common Side Effects

The most common side effects of tamsulosin include1:

  • Headache
  • Dizziness
  • Blurred Vision
  • Cold-like symptoms
  • Infection
  • Abnormal ejaculation
  • Loss of libido
  • Fatigue or drowsiness
  • Diarrhea
  • Nausea
  • Back pain
  • Chest pain
  • Cough
  • Insomnia
  • Problems with your teeth


Serious Side Effects

Rare side effects reported for tamsulosin include1:

  • Dyspnea
  • Abnormal heart beat
  • Very low blood pressure
  • Severe skin reactions
  • Constipation
  • Vomiting
  • Dry mouth
  • Problems seeing
  • Nose bleeds
  • Persistent erection
  • Allergic reactions (hives, swelling of the face or throat, problems breathing)


Warnings for Tamsulosin Use

General Warnings

Risk of Injury

Tamsulosin can cause dizziness or fainting in some individuals. When you first start taking tamsulosin, you should avoid situations that might put you in danger if you were to get dizzy or faint.1


Though rare, taking tamsulosin may cause you to develop a persistent erection (priapism). You should be aware that this is a serious medical situation.1

If left untreated, this can cause permanent impotence. You may never be able to experience an erection or orgasm again. Please seek immediate medical attention if you develop an erection without being aroused.1

Floppy-Iris Syndrome

If you are taking or have taken tamsulosin in the last 9 months and you need eye surgery, you should tell your surgeon. Tamsulosin and other α1-receptor blockers may increase your risk of developing Floppy-Iris Syndrome.1

Floppy-Iris Syndrome is when the iris (the colored part of your eye), slips out of place, or out of an incision, following surgery.1,16

If the surgeon knows that you are at risk for this syndrome, she can change how she does your surgery to help prevent this from happening.1

Prostate Cancer

The symptoms of BPH can be similar to the symptoms of prostate cancer.1

Improvement of your symptoms with tamsulosin does not mean that you cannot have prostate cancer.1

You should continue to undergo normal prostate cancer screenings.1

Please do not ignore any changes in your symptoms as “simply” your BPH. They may indicate a more serious problem.1

If you are concerned about any changes in your symptoms, please talk to your doctor.

Warnings for Individuals with Sulfa Allergies

Individuals with a sulfa allergy may have an allergic reaction to tamsulosin.1

“Sulfa” refers to a drug containing a sulfonamide group in its structure.17

Tamsulosin has one such structure and may be able to trigger a sulfa allergy.18


Figure 3: Structures of Sulfonamide (above) and Tamsulosin (below).

Red box highlights the sulfonamide group in the structure of tamsulosin.

Sulfonamide Group by Benjah-bmm27 is in the public domain.

Tamsulosin Structural Formulae by is in the public domain; original modifications.

If you have a known, serious sulfa allergy, it may be safer for you to use another drug to control your urinary symptoms.1


Warnings for Individuals with Kidney Disease or Liver Disease

Tamsulosin is believed to be safe for individuals with mild kidney or liver disease. There are no recommendations for decreased dosage.1

However, tamsulosin has not been tested in end-stage kidney or liver failure. It is possible that you may experience adverse effects taking tamsulosin if you have one of these conditions. What these effects might be is not yet known.1

Warnings for Pregnant Women

Though tamsulosin was not originally intended for women, scientists have done animal studies to see how it affects unborn babies.1

Based on these studies, the FDA has classed tamsulosin as a category B pregnancy drug.1

This means the animal studies showed no negative effects in unborn animals.1

No studies have been done on human mothers during pregnancy to confirm these results. There is some risk that tamsulosin may have adverse effects on human pregnancies.1

If your doctor is thinking about prescribing tamsulosin off-label for you, please tell him if you are pregnant or plan to become pregnant.

Warnings for Nursing Women

Since tamsulosin was not originally not intended for women, no studies have been done to see if it is safe while nursing.1


Tamsulosin Compared to Other Similar Drugs

Tamsulosin vs. Dutasteride

Dutasteride is another medication that can be used to treat the symptoms of BPH.19

Dutasteride works by blocking the activity of the 5α-reductase enzyme.19

The 5α-reductase enzyme normally converts testosterone into a metabolite called 5α-dihydrotestosterone (DHT).19

DHT is a growth hormone that works on reproductive organs, like the prostate. Blocking its production by 5α-reductase enzyme slows down prostate growth.19

Dutasteride has different side effects, risks, and drug interactions from tamsolusin. Depending on your medical history, your doctor may decide that dutasteride or tamsolusin is a safer or more effective option for you.



Though not yet studied in detail, dutasteride might be unsafe for those with liver disease. If you have severe liver disease, your doctor may decide tamsulosin is safer for you.19

Dutasteride is much less safe for individuals trying to become pregnant.19

Dutasteride is a category X pregnancy drug. It is associated with birth defects, particularly of the genitals of male babies.19

Women who are pregnant or trying to become pregnant should not handle dutasteride. It can be absorbed through their skin and harm the baby.19

Dutasteride is found in sperm of men taking it. It can make it more difficult to get pregnant. It can also increase the risk of birth defects, should pregnancy occur.19

Tell your doctor if you and your partner are trying to get pregnant. Tamsulosin is likely a safer option for you.

Side Effects

The common side effects associated with dutasteride only affect sexual health.19

Similar to tamsulosin, dutasteride may cause19:

  • Impotence
  • Abnormal ejaculation
  • Loss of libido

Additionally, dutasteride may also cause growth of breast tissue.19

            Drug Interactions

Several medications that interact with tamsulosin do not interact with dutasteride.1,19

These include1,19:

  • Paroxetine
  • Erythromycin
  • Terbinafine
  • Cimetidine
  • α-Receptor Blockers
  • PDE5 inhibitors
  • Warfarin

If you are taking any of these medications, dutasteride may be safer for you.

Dutasteride may interact with calcium channel blockers, however, which tamsulosin does not.1,19 If you are on a calcium channel blocker, your doctor may decide that tamsulosin is safer for you.

Tamsulosin vs. Finasteride

Finasteride is a 5α-reductase enzyme inhibitor, like dutasteride.20

Finasteride can also be used to improve the symptoms of BPH, though it is only approved by the FDA to treat hair loss in men.20

Risks and Side Effects

Finasteride has essentially the same side effects and risks as dutasteride. Finasteride is also a less safe choice than tamsulosin if you have liver disease or are trying to become pregnant.19,20

Drug Interactions

Unlike tamsulosin and dutasteride, scientists have found no drug interactions with finasteride.1,19,20

If you are on multiple medications, your doctor may chose finasteride to treat your BPH symptoms.



Tamsulosin Drug Interactions

Tamsulosin and Inhibitors of CYP3A4 or CYP2D6

Tamsulosin is broken down by the liver enzymes CYP3A4 and CYP2D6.1

Taking tamsulosin at the same time as medications that decrease the activity of these enzymes can increase the amount of tamsulosin in your body. This increases your risk of side effects or overdose.1

Medications that inhibit these enzymes include1:

  • Ketoconazole
  • Erythromycin
  • Paroxetine
  • Terbinafine


Tamsulosin and Cimetidine

Cimetidine is a histamine H2-receptor blocker. Doctors prescribe it to treat ulcers and gastric reflux disease.21

Taking cimetidine at the same time you are taking tamsulosin may decrease your body’s ability to break down tamsulosin. This can increase the amount of tamsulosin and increase your risk of side effects and overdose.1,21


Tamsulosin and Other α-Receptor Blockers

Taking tamsulosin with other α-receptor blockers is unsafe. Since they all work by blocking the same receptors, medications in this class of drugs taken together can have additive effects. This increases your risk of side effects or overdose.1

Examples of other α-Receptor Blockers include22:

  • Doxazosin
  • Prazosin
  • Terazosin
  • Silodosin
  • Alfuzosin
  • Guanadrel
  • Guanethidine
  • Mecamylamine


Tamsulosin and PDE5 Inhibitors

PDE5 inhibitors block the activity of the phosphodiesterase enzyme 5.23 This enzyme normally helps make signaling molecules that tell the body to increase blood pressure. Blocking this enzyme helps lower blood pressure.23

Since tamsulosin can also lower blood pressure, taking these two types of medications together can cause the blood pressure to go too low.1,23

 Tamsulosin and Warfarin

Studies have not been able to rule out an interaction between tamsulosin and warfarin.

You should be careful when taking these two drugs together. You may be at an increased risk of excessive bleeding.1


Abuses of Tamsulosin

Tamsulosin does not cause any sort of high. It is not believed to have any addictive properties.1

The risk of abuse or misuse of tamsulosin is very low.1


Tamsulosin Overdose

The major risk associated with tamsulosin overdose is an extreme drop in blood pressure.1

This may lead to fainting or loss of consciousness.1

If you suspect a tamsulosin overdose, keep the person lying down to help stabilize their blood pressure.1 Then call for medical help.

Doctors can monitor the person’s blood pressure and provide medications and other treatment options to stabilize their blood pressure.1


Tamsulosin FAQs

  • When should I take tamsulosin? Day or night?

It doesn’t matter if you take tamsulosin in the morning or at night. Studies have found no difference in how well tamsulosin treats symptoms of BPH when taken in the morning or at night.24

Whenever you choose to take tamsulosin, however, you should be consistent. Tamsulosin should be taken at the same time each day.1

  • How long does it take tamsulosin to work?

You will likely see improvements in your symptoms after your first dose of tamsulosin.25

Your symptoms will likely continue to improve for around a week before leveling off. It takes about a week for the medicine to exert its full effects.25

  • How long should I take tamsulosin?

There is no recommended length of therapy with tamsulosin. You should take tamsulosin as long as your doctor has ordered you to.1

Do not stop taking tamsulosin without talking to your doctor.

  • How much tamsulosin can I take?

You should take the amount of tamsulosin that your doctor prescribed to you.

If you are taking tamsulosin to treat the symptoms of BPH, this is likely 0.4 mg or 0.8 mg per day. You should take this dose once a day, at the same time each day.1

  • Does Flomax cause constipation?

Constipation has rarely been reported as a side effect of Flomax.1

It is possible for you to experience new or worsening constipation after starting Flomax.1

  • How long does it take to pass a kidney stone with Flomax?

Kidney stones may take several days to several weeks to pass.13,14

If you have a small stone, Flomax is unlikely to speed up the passing process.13

If you have a large stone, Flomax might speed up the process by around 3 or 4 days.13 The whole process might still take a week or longer, even with Flomax.13



  1. Astellas Pharma Inc. Flomax Prescribing Information. Last updated October, 2014. Accessed August 18, 2017. PDF.
  2. FDA. Generic Drug Round Up: April 2010. Last updated April 21, 2010. Accessed August 18, 2017.
  3. Cotecchia S. The alpha1-adrenergic receptors: diversity of signaling networks and regulation. Journal of receptor and signal transduction research.2010;30(6):410-419. Doi: 10.3109/10799893.2010.518152
  4. Paolone DR. Benign prostatic hyperplasia. Clinics in geriatric medicine. 2010;26(2):223-239. Doi: 10.1016/j.cger.2010.02.010
  5. Gandaglia G, Briganti A, Gontero P, et al. The role of chronic prostatic inflammation in the pathogenesis and progression of benign prostatic hyperplasia (BPH). BJU international. 2013;112(4):432-441. Doi: 10.1111/bju.12118
  6. Swaminathan A. Stop prescribing tamsulosin for all kidney stones. Emergency Medicine News. 2016;38(10):14. Doi: 10.1097/01.EEM.0000503375.61563.93
  7. Worcester EM, Coe FL. Clinical practice. Calcium kidney stones. The New England journal of medicine. Sep 02 2010;363(10):954-963. Doi: 10.1056/NEJMcp1001011
  8. Andersson KE, Chapple CR, Cardozo L, et al. Pharmacological treatment of overactive bladder: report from the International Consultation on Incontinence. Curr Opin Urol. 2009;19:380-394. Doi: 10.1097/MOU.0b013e32832ce8a4
  9. Banakhar MA, Al-Shaiji TF, Hassouna MM. Pathophysiology of overactive bladder. Int Urogynecol J. 2012;23:975-982. Doi: 10.1007/s00192-012-1682-6
  10. Kwon J, Cho K, Oh C, et al. The beneficial effect of alpha-blockers for ureteral stent-related discomfort: systematic review and network meta-analysis for alfuzosin versus tamsulosin versus placebo. BMC Urology. 2015;15:55. Doi: 10.1186/s12894-015-0050-5
  11. Lamb AD, Vowler SL, Johnston R, Dunn N, Wiseman OJ. Meta-analysis showing the beneficial effect of α-blockers on ureteric stent discomfort. BJU international. 2011;108(11):1894-1902. Doi: 10.1111/j.1464-410X.2011.10170.x
  12. Robinson D, Cardozo L, Terpstra G, Bolodeoku J. A randomized double-blind placebo-controlled multicentre study to explore the efficacy and safety of tamsulosin and tolterodine in women with overactive bladder syndrome. BJU international. 2007;100:840-845. Doi: 10.1111/j.1464-410X.2007.07162.x
  13. Furyk JS, Chu K, Banks C, et al. Distal Ureteric Stones and Tamsulosin: A Double-Blind, Placebo-Controlled, Randomized, Multicenter Trial. Annals of emergency medicine. 2016;67(1):86-95 e82. Doi: 10.1016/j.annemergmed.2015.06.001
  14. Pickard R, Starr K, MacLennan G, et al. Medical expulsive therapy in adults with ureteric colic: a multicentre, randomised, placebo-controlled trial. Lancet. Jul 25 2015;386(9991):341-349. Doi: 10.1016/S0140-6736(15)60933-3
  15. Kim S, Choi HS, Kwon D. The α1 Adrenoceptor Antagonist Tamsulosin for the Treatment of Voiding Symptoms Improves Nocturia and Sleep Quality in Women. Urol J. 2014;11(3):1636-1641.
  16. Flach AJ. Intraoperative Floppy Iris Syndrome: Pathophysiology, Prevention, and Treatment Trans Am Ophthalmol Soc. 2009;107:234-241. https://www.ncbi.nlm.
  17. T.E. K, Hackett PH. Acetazolamide and Sulfonamide Allergy: A Not So Simple Story. High altitude medicine & biology. 2010;11(4):319-323. Doi: 10.1089/ham.2010.1051
  18. Nanubolu JB, Sridhar B, Ravikumar K. Polymorphism in R-tamsulosin (an alpha blocker): The unexpected manifestation of a sulfonamideo-diethoxybenzene heterosynthon. Journal of Molecular Structure. 2014;1078:43-60. Doi:
  19. GlaxoSmithKline. Adovart (Dutasteride) Prescribnig Information. Last updated February 2008. /2008/021319s015lbl.pdf. Accessed August 21, 2017. PDF.
  20. Merck & Co, Inc. Propecia (Finasteride) Prescribing Information. Last updated December 2010. /020788s018lbl.pdf. Accessed August 21, 2017. PDF
  21. Kubecova M, Kolostova K, Pinterova D, Kacprzak G, Bobek V. Cimetidine: An anticancer drug? European Journal of Pharmaceutical Sciences. 2011;42(5):439-444. Doi:
  22. Antiadrenergic agents, peripherally acting. Drugs.Com. 2017. Accessed August 22, 2017.
  23. Elhwuegi AS. The Wonders of Phosphodiesterase-5 Inhibitors: A majestic history. Ann Med Health Sci Res. 2016;6(3):139-145. Doi: 10.4103/2141-9248.183943
  24. Michel MC, Neumann HG, Mehlburger L, Schumacher H, Goepel M. Does the time of administration (morning or evening) affect the tolerability or efficacy of tamsulosin? BJU international. Jan 2001;87(1):31-34.
  25. Lowe FC. Summary of Clinical Experiences With Tamsulosin for the Treatment of Benign Prostatic Hyperplasia. Rev Urol. 2005;7(suppl 4):S13-S21.


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