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Last updated: Nov 10, 2020
5 min read

Tamsulosin (Flomax) warnings: be aware of these issues

chimene richa

Medically Reviewed by Chimene Richa, MD

Written by Michael Martin


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

If you’ve recently been prescribed tamsulosin, you may be wondering if it’s safe for you. Always tell your healthcare provider about all medications and supplements you’re currently taking before you begin taking tamsulosin or any new medication. 

Doing this will reduce the chance of encountering potentially dangerous drug interactions. Some people with certain medical conditions cannot take tamsulosin or should use it with caution. Your healthcare professional can help you navigate this path, but you should know some important drug information.

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What is tamsulosin used for?

Tamsulosin is FDA-approved to treat benign prostatic hyperplasia or hypertrophy (BPH), also known as an enlarged prostate; it belongs to the alpha-blocker medication class. Other examples of this drug class include prazosin (brand name Minipress), doxazosin (brand name Cardura), alfuzosin (brand name Uroxatral), terazosin (brand name Hytrin), and silodosin (brand name Rapaflo).

As the prostate gets larger, it puts pressure on the urethra (the tube that carries urine from your bladder out through the penis). This pressure can cause common BPH symptoms, like urinary retention (incomplete empty of the bladder); needing to urinate more often, especially at night; trouble starting urination; a weak flow of urine; starting and frequently stopping during urination and having to strain to urinate (AUA, 2020). Tamsulosin helps by relaxing your bladder and prostate muscles, allowing urine to flow easier and improving your BPH symptoms. Because prostate cancer and BPH can exist simultaneously, you should be screened for prostate cancer before beginning tamsulosin and regularly thereafter (DailyMed, 2017

Tamsulosin is also prescribed “off-label” for chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) in men and ureteral calculi (kidney stones in the ureter) (UpToDate, n.d.).

Flomax generic

Tamsulosin is the generic version of the brand-name drug Flomax. It is the same medication and, depending on your prescription plan, may be a less expensive alternative to Flomax. Generic medications need to through rigorous testing to make sure that they are as safe and effective as brand name drugs. 

Tamsulosin warnings

People with certain medical issues or who experience certain side effects should take special caution when using tamsulosin. In some cases, it should be avoided altogether. Tamsulosin is not approved for use in women. Potential issues to be aware of include: 

Chest pain

If you develop chest pain while taking tamsulosin, you should seek immediate medical attention. People with heart problems, like cardiovascular disease, may develop chest pain or angina as a warning sign of poor blood flow to the heart. If you already experience chest pain, let your healthcare provider know (UpToDate, n.d.). 

Heart failure

People who have heart failure should be careful when taking tamsulosin because it can worsen existing heart failure and lead to more heart problems. (UpToDate, n.d.).  

Problems during eye surgery

People who want to have eye surgery, like cataract surgery or glaucoma surgery, should not start taking tamsulosin or other alpha-blockers. In some people, tamsulosin changes the iris and makes it “floppy”—this can lead to problems during eye surgery. This intraoperative floppy iris syndrome (IFIS) can happen even if you stopped your tamsulosin months before surgery. For this reason, your healthcare provider may recommend not starting the drug if you anticipate eye surgery in the future—wait until after surgery if you can (DailyMed, 2017).

Sulfonamide allergy

Rarely, people with allergies to sulfonamide or “sulfa” drugs have had an allergic reaction to tamsulosin. Be careful when taking tamsulosin if you experienced a sulfa allergy in the past. Avoid taking it if your sulfa allergy was severe (swelling, trouble breathing, etc.) (DailyMed, 2017). 

Orthostatic hypotension 

If you’re taking medication for high blood pressure (hypertension), consult your healthcare provider about whether it’s safe and advisable for you to take tamsulosin as well. Taking blood pressure medications with tamsulosin can increase the risk of orthostatic hypotension (Biaggioni, 2018).

Orthostatic hypotension is a sudden drop in blood pressure (hypotension) that can happen when you stand up from a sitting position. This low blood pressure can cause dizziness, vertigo, and fainting (syncope). Some people experience this with tamsulosin, especially when first starting tamsulosin or with an increased dose. If you’re just beginning treatment with tamsulosin or are changing the dose, be wary of orthostatic hypotension and avoid situations where injury can occur (DailyMed, 2017). 

Furthermore, if you have low blood pressure, use tamsulosin with caution to prevent your blood pressure from dropping even further. 


Rarely, tamsulosin (and other alpha antagonist drugs) can cause priapism, a prolonged, painful erection lasting more than four hours. This condition requires emergency medical attention, and you should seek medical help immediately. Left untreated, priapism can lead to permanent penile or erectile dysfunction (DailyMed, 2017).

Tamsulosin side effects

Like all medications, tamsulosin has side effects that you should be aware of. Some common side effects of tamsulosin include headache, dizziness, common cold symptoms (like a runny nose or nasal congestion), diarrhea, drowsiness, and abnormal ejaculation (DailyMed, 2017).

However, more serious side effects can occur with tamsulosin (UpToDate, n.d.) and include low blood pressure or fainting (syncope), especially when standing from a sitting position (orthostatic hypotension). Some people may experience angina (chest pain) or have a severe allergic reaction to tamsulosin, such as developing a skin rash, swelling, and trouble breathing. If you experience any of these symptoms, seek medical attention immediately.

This may not include all side effects of tamsulosin. Ask your healthcare professional or pharmacist for medical advice. 

Tamsulosin interactions

Before starting tamsulosin, inform your healthcare provider of other medications, whether prescription drugs or over-the-counter medicines, that you are taking as tamsulosin may interact with certain drugs, including:

Sildenafil and other PDE5 inhibitors

Phosphodiesterase-5 (PDE5) inhibitors are oral medications used to treat erectile dysfunction (ED). They’re vasodilators (meaning they work by dilating blood vessels), which lower blood pressure. Taking both tamsulosin and PDE5 inhibitors may cause low blood pressure (hypotension) (DailyMed, 2017).

Examples of PDE5 inhibitors include: 

Seek medical advice to determine if it’s safe to take tamsulosin while you’re taking a PDE5 inhibitor.

CYP3A4 and CYP2D6 blockers 

CYP3A4 and CYP2D6 are two liver enzymes in the cytochrome P450 system that help the liver metabolize tamsulosin. Any drug that blocks or inhibits CYP3A4 and CYP2D6 affects the breakdown of tamsulosin and can increase its concentration in the body. A higher concentration may increase your risk of adverse effects, and your healthcare provider may need to adjust your medication dose (DailyMed, 2017).

Examples of CYP3A4 and CYP2D6 blockers include:

  • Cimetidine 
  • Ketoconazole 
  • Erythromycin
  • Terbinafine
  • Paroxetine 

In summary

Tamsulosin works well in improving BPH symptoms in most people. However, if you have certain medical conditions or take other medications, you should be aware of the warnings that go along with using tamsulosin. Consult with your healthcare provider for more information.


  1. American Urology Association (AUA). (2020). Urology Care Foundation: What is benign prostatic hyperplasia? Retrieved on Sep. 8, 2020 from
  2. Biaggioni, I. (2018). Orthostatic Hypotension in the Hypertensive Patient. American Journal of Hypertension, 31(12), 1255–1259. Retrieved from
  3. DailyMed. (n.d.). FLOMAX- tamsulosin hydrochloride capsule. Retrieved Sep. 10, 2020 from
  4. National Health Service (NHS). (2019, November 14). Tamsulosin. Retrieved Sep. 10, 2020 from
  5. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (2018). Alpha 1 Adrenergic Receptor Antagonists. In LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. Retrieved from
  6. UpToDate. (n.d.). Tamsulosin: Drug information. Retrieved on Sep. 8, 2020 from

Dr. Chimene Richa is a board-certified Ophthalmologist and Senior Medical Writer/Reviewer at Ro.