Can You Take Doxasozin And Flomax Together?

In our latest question and answer, the pharmacist discusses why Flomax (tamsulosin) and doxazosin are not recommended to be taken together.


I am 76 years old and currently being treated for BPH. I have been taking doxazosin 4 mg daily for several years and my urologist has prescribed tamsulosin 0.4 mg by mouth once a day. I have experienced a severe drop in blood pressure. I have also read not to take both so I dropped the doxazosin, but now I have more difficulty urinating. If I take the doxazosin, my flow was great but my blood pressure fell through the floor. Now, my question is, what are my alternatives? Am I doomed to have a flow problem? It seems like there should be something else I can use.

Asked by Bernie On Jun 12, 2022

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Jun 13, 2022
Last updated Apr 11, 2024

Key points

  • Flomax (tamsulosin) and doxazosin are generally not given together as they work the same way (i.e. have the same mechanism of action)
  • Taking both together increases the risk of side effects such as low blood pressure, dizziness, lightheadedness, and ejaculatory dysfunction.
  • Several other treatment options exist for BPH including 5-alpha reductase inhibitors (e.g. Avodart and Proscar) and PDE-5 inhibitors (e.g. Cialist)

Hello and thanks for your great question!

So, there are two parts to this I want to answer.

First, I want to talk about why you generally don't want to take doxazosin and Flomax (tamsulosin) together, and then I'll discuss some other treatment options for BPH (benign prostatic hyperplasia) that you should talk to your doctor about.

Problems Taking Doxasozin And Flomax Together

The primary reason it isn't generally recommended to take doxazosin and Flomax together is that they work the same way, which increases the risk of side effects occurring.

Both drugs are considered 'alpha-1 blockers', meaning they both block alpha-1 receptors in the body.

Alpha-1 receptors are all located all over the body, including in blood vessels, the bladder, and the prostate.

When alpha-1 receptors are blocked in the blood vessels, it produces 'vasodilation', opening them up, which, in turn, lowers blood pressure.

In the prostate and bladder, blocking alpha-1 receptors relaxes the smooth muscle, resulting in increased urine flow.

Now, even though doxazosin and Flomax (tamsulosin) work in the same manner, there is an important distinction between them.

Flomax (tamsulosin) is far more of a selective alpha-1 blocker than doxazosin is, meaning it more selectively acts on alpha-1 receptors located in the prostate and bladder versus other places in the body.

Doxazosin is a non-selective alpha-1 blocker, and acts on, more or less, alpha receptors located all over the body. Due to this, doxazosin is generally associated with more side effects than Flomax, and a greater percentage of individuals experience fatigue, drowsiness, lightheadedness, and low blood pressure when compared to Flomax. This is also why doxazosin is sometimes used to treat high blood pressure (Flomax is not used for this reason).

Even though Flomax is selective, it still does carry the side effect risk of lowering blood pressure (just not as much as doxazosin).

Taking Doxazosin and Flomax together is considered a 'therapeutic duplication' because, again, they work essentially the same way.

Taking both can be more effective than taking either alone, but the increase in effectiveness usually isn't too significant and puts you at risk for more side effects, so it generally is not recommended.

You mention in your question that your 'blood pressure dropped through the floor', which is exactly what the precaution would be for someone taking doxazosin and Flomax together. It makes sense to just take one or the other (based on your doctor's direction of course).

Other potential side effects to be concerned about are dizziness, fatigue, lightheadedness and ejaculatory dysfunction.

Alternative Therapy Options For BPH

This gets us to talking about what your other options are.

There are other alpha-1 blockers available on the market, most notably alfuzosin ER.

You may find it more effective than what you have tried before, and it carries the lowest risk of ejaculatory dysfunction among alpha-1 blockers

There are other drug classes available that are indicated for BPH as well. They include:

5-alpha reductase inhibitors can be used alone for BPH or in combination with alpha-1 blockers.

5-alpha-reductase inhibitors actually shrink the prostate and can delay the need for surgery in the future.

They are not a quick fix though and can take 6-12 months to really start working. They also have been linked to sexual dysfunction and an increased risk of certain types of prostate cancer.

In regard to PDE-5 inhibitors, you may recognize the drug name Cialis, since it's commonly used for erectile dysfunction.

Lower doses of Cialis taken daily are effective for BPH. It is generally considered a treatment option in those that have erectile dysfunction and cannot tolerate alpha-1 blockers (or in those who have not responded to them).

There is a drug on the market that contains both a 5-alpha reductase inhibitor and PDE-5 inhibitor, called Entadfi (finasteride and tadalafil.). However, it would likely be less expensive to just take both separately.

Final Words

I hope this information helped answer your question!

I highly recommend you talk to your doctor about your options and feel free to reach back out to us with any further questions.


  • Management of Lower Urinary Tract Symptoms Attributed to Benign Prostatic Hyperplasia: AUA GUIDELINE PART I-Initial Work-up and Medical Management, PubMed
  • Benign Prostatic Hyperplasia: An Overview, PubMed
  • Canadian Urological Association guideline on male lower urinary tract symptoms/benign prostatic hyperplasia (MLUTS/BPH): 2018 update, PubMed

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at [email protected]! You can also connect with Dr. Brian Staiger on LinkedIn.

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