How Flomax Works for Kidney Stones: Dosage, Time to Pass, and More

The idea of passing a kidney stone can sound scary. Yet, it’s something that 6% to 11% of people in the U.S. will face in their lifetime. Kidney stones can come in all shapes and sizes, but they all share the pain they can cause when passed. 

Most kidney stones can pass on their own. But sometimes they’re too big to make it through. In this case, medications are sometimes used to create extra room for it to pass. This is called medical expulsive therapy (MET). Flomax (tamsulosin) is a medication commonly used off-label for this purpose.

Here we'll talk about Flomax for kidney stones: how it works, potential benefits, and more.

How does Flomax help pass kidney stones?

Flomax belongs to a class of medications called alpha-1 blockers. These medications are commonly used to treat an enlarged prostate, also called benign prostatic hyperplasia (BPH). Other examples include Rapaflo (silodosin) and Uroxatral (alfuzosin). 

Alpha-1 blockers cause prostate muscles to relax, making it easier to pee. In the case of kidney stones, they can help widen the tube that connects the kidney with the bladder (ureter). This gives a larger stone more room to pass.

Evidence suggests that alpha-1 blockers like Flomax may be most effective for kidney stones larger than 5 mm. One randomized controlled trial showed faster time to kidney stone passage and less pain medication needed with Flomax compared to placebo (a pill with no medication in it). 

What is the typical dosage for kidney stones?

The typical Flomax dosage for kidney stones is 0.4 mg taken by mouth once daily. The medication is taken until the kidney stone is passed.  

How long does Flomax take to help pass kidney stones?

Kidney stones may take days to several weeks to pass. Usually, the smaller the stone, the quicker and more easily it can pass. How long it takes can depend on the size and location. With this in mind, Flomax may help a kidney stone pass a few days faster than without medication.

If it’s been 4 to 6 weeks and the stone still hasn’t passed, contact your healthcare provider. They may need to perform a procedure. See them right away if you develop signs of an infection (like fever, chills) or persistent pain that has gotten worse. This could be a sign of a urinary tract infection (UTI).

Are there any side effects?

As with most medications, Flomax has some side effects that you should be aware of. These include:

• Headache

• Dizziness

• Stuffy nose

• Infection

• Abnormal ejaculation

• Weakness

• Back pain

• Diarrhea

Flomax can make you feel dizzy or feel like you’re going to pass out, especially when changing positions (like going from sitting to standing). See how you respond to the medication first before driving or performing tasks that could result in injury. 

Alternatives and pain meds for kidney stones

The American Urological Association (AUA) strongly recommends alpha-1 blockers like Flomax for MET. Nifedipine (Procardia) has also been studied for MET. But there’s not enough evidence to recommend it.

As mentioned earlier, kidney stones can be painful. So, part of the treatment is keeping the pain under control. Your healthcare provider may recommend a nonsteroidal anti-inflammatory drug (NSAID), like ibuprofen (Advil, Motrin), to help.

Depending on the cause of your kidney stone, your healthcare provider may recommend dietary changes or prescribe medications to prevent another one from happening. 

Can you pass a kidney stone on your own?

Depending on the size and location of your kidney stone, it may pass on its own without using medications. You may be told to drink more water to pee more often and help push the stone out. 

This could take days or weeks. And for many people, this could be uncomfortable. Your healthcare provider will let you know what options you have. They’ll also tell you what to watch out for whether intervention is needed. This includes signs of a kidney infection or UTI or very severe pain.

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Written by:

Timothy Aungst, PharmD

Timothy Aungst, PharmD, has worked in pharmacy practice for a decade. He has served as an associate professor of pharmacy practice, a clinical pharmacist in outpatient cardiology management, and now in home healthcare.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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