Does Flomax relax the ureters? A look at Tamsulosin's role in kidney stone expulsion

October 10, 2025 •

4 min read

Recent meta-analyses indicate that tamsulosin, the active ingredient in Flomax, is associated with a higher stone expulsion rate and shorter expulsion time for ureteral stones. It works by relaxing the ureteral smooth muscle, which helps relieve pain and speed up the passage of kidney stones.

Quick Summary

Flomax, an alpha-blocker, relaxes the smooth muscle of the ureters to help pass kidney stones. This off-label use is known as medical expulsive therapy, often prescribed for smaller stones.

Key Points

Ureteral Relaxation: Flomax (tamsulosin) relaxes the smooth muscles of the ureters by blocking alpha-1A adrenergic receptors, which helps dilate the ureteral lumen and inhibit spasms.
Medical Expulsive Therapy (MET): This relaxation effect makes Flomax an effective medication for facilitating the passage of small to medium-sized ureteral stones.
Optimal Stone Size: Evidence suggests Flomax is most beneficial for stones between 5mm and 10mm, especially those located in the lower ureter.
Reduced Pain and Expulsion Time: Patients using Flomax for MET often experience reduced pain, fewer colic episodes, and a shorter overall time for stone passage.
Prescribed Use: Flomax is a prescription medication and should only be used under the direction of a healthcare provider.
Potential Side Effects: Common side effects include dizziness, headache, and abnormal ejaculation. A doctor should be informed of the medication's use, particularly before eye surgery, due to the risk of Intraoperative Floppy Iris Syndrome (IFIS).

What is Flomax and How Does it Work?

Flomax, the brand name for tamsulosin, is a type of medication known as an alpha-blocker. While its primary, FDA-approved use is for treating the symptoms of an enlarged prostate (benign prostatic hyperplasia or BPH), it also has a significant off-label application in the field of urology. Tamsulosin works by selectively blocking alpha-1A adrenergic receptors. These receptors are abundant in the smooth muscle tissues of the prostate, bladder, and urethra, and also in the ureters. By blocking these receptors, Flomax causes the muscles in these areas to relax.

For men with BPH, this muscle relaxation improves urine flow. For patients with ureteral stones, this same mechanism helps widen the narrow urinary tract tube (the ureter) and reduce muscular spasms, making it easier for a stone to pass through.

The Mechanism of Action on Ureteral Smooth Muscle

When a kidney stone travels from the kidney to the bladder, it can become lodged in the ureter, causing intense pain known as renal colic. This pain is largely due to the ureter's muscular walls contracting around the stone in an attempt to push it along. Flomax's ability to block alpha-1A adrenergic receptors specifically addresses this issue by:

Relaxing ureteral smooth muscle: The ureteral walls become less constricted, reducing the painful pressure caused by muscle spasms.
Inhibiting ureteral spasms: By calming the involuntary muscular contractions, the medication helps to alleviate the severe, cramp-like pain associated with renal colic.
Dilating the ureteral lumen: The relaxation of the muscle allows for a wider inner diameter of the ureter, providing a larger pathway for the stone to move through.

Flomax for Medical Expulsive Therapy (MET)

This therapeutic strategy of using medication to help pass ureteral stones is called Medical Expulsive Therapy (MET). Numerous studies and meta-analyses have investigated the efficacy of tamsulosin for MET, with findings supporting its use in specific cases.

Evidence of Efficacy: A meta-analysis published in 2019 found that tamsulosin was associated with a higher stone expulsion rate and shorter expulsion time compared to a control group.
Optimal Candidates: Flomax is generally most effective for patients with smaller ureteral stones, particularly those between 5mm and 10mm and located in the distal (lower) part of the ureter. It may not offer a significant advantage for very small stones that would likely pass on their own.
Decreased Pain: Many studies also note that patients taking tamsulosin for ureteral stones require less pain medication and experience fewer colic episodes.

Comparing Flomax with Other Kidney Stone Strategies

Different approaches can be used to manage ureteral stones, depending on their size, location, and the patient's symptoms. Here is a comparison of common strategies:


Method	Mechanism	Efficacy for Stone Passage	Pain Management	Typical Duration
Flomax (Tamsulosin)	Relaxes ureteral smooth muscle via alpha-blockade, widening the ureter.	Increases expulsion rate, especially for stones 5-10mm in the lower ureter.	Reduces painful spasms and the need for analgesics.	Days to several weeks, until the stone passes.
Observation / Hydration	Allows the stone to pass naturally with the help of increased fluid intake.	Effective for very small stones (<5mm) and stones with no significant symptoms.	Managed with over-the-counter NSAIDs (e.g., ibuprofen).	Can vary from days to weeks depending on stone size.
NSAID Pain Management	Reduces inflammation and pain, but does not directly aid in stone passage.	No direct impact on stone expulsion; used for symptom relief.	Effective for moderate pain; may not be sufficient for severe renal colic.	Used as needed for pain relief.
Other Alpha-Blockers	Similar mechanism to Flomax, relaxing smooth muscle.	Comparable efficacy to Flomax for distal ureteral stone expulsion.	Provides similar pain reduction benefits.	Similar to Flomax, taken until the stone passes.

How to Take Flomax for Ureteral Stones

It is crucial to follow a healthcare provider's instructions when taking Flomax for any condition. Consistent administration as directed by a healthcare professional is important.

Here are some general points about proper administration:

Taking the capsule around the same time each day, often after a meal, can help ensure consistent absorption.
Swallow the capsule whole with water. Avoid crushing, chewing, or opening it, as this can affect how the medication is released over time.
Continue taking the medication for the duration prescribed by your doctor.
If a dose is missed, follow your doctor's advice. Do not take extra medication to make up for a missed dose.

Potential Side Effects and Precautions

Like all medications, Flomax can cause side effects. Awareness of these is important for patient safety and comfort.

Common Side Effects

Dizziness and lightheadedness: These are common, especially when first starting the medication, due to a possible drop in blood pressure when standing up (orthostatic hypotension).
Ejaculation problems: Abnormal or decreased ejaculation is a frequently reported side effect.
Headache.
Stuffy or runny nose.

Important Precautions

Intraoperative Floppy Iris Syndrome (IFIS): This is a rare complication that can occur during cataract surgery in patients who have taken or are currently taking alpha-blockers. Inform your eye surgeon about your use of Flomax.
Drug Interactions: Inform your doctor of all other medications you are taking, especially strong CYP3A4 inhibitors (e.g., ketoconazole) and other alpha-blockers.
Allergies: Though rare, allergic reactions can occur.

Conclusion

To directly answer the question, yes, Flomax does relax the ureters. By acting as an alpha-blocker, tamsulosin reduces muscle contractions in the ureteral walls, helping to facilitate the passage of kidney stones and reduce associated pain. This off-label use, known as Medical Expulsive Therapy, is well-supported by clinical evidence, particularly for distal ureteral stones between 5mm and 10mm. While generally effective, it is important to be aware of potential side effects and to use the medication under a doctor's supervision. For more information on tamsulosin's efficacy in MET, see this study abstract from the NIH.

Frequently Asked Questions

The time it takes for a kidney stone to pass with the help of Flomax can vary, typically ranging from a few days to several weeks. The total time depends on the size and location of the stone. It is generally recommended to continue taking the medication until the stone has passed, as directed by your doctor.

Flomax's primary approved use is to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia or BPH), improving urine flow. It is also used off-label to help pass kidney stones.

Common side effects of Flomax include dizziness, headache, and problems with ejaculation. Orthostatic hypotension (a drop in blood pressure when standing up) can also occur, especially when starting the medication.

Flomax is generally most effective for smaller stones, particularly those between 5mm and 10mm. For larger stones, other treatment options, potentially including surgical intervention, may be necessary. Your doctor will determine the best course of action.

Yes, Flomax is a prescription medication and must be obtained with a doctor's authorization. Your healthcare provider will determine if it is the right treatment for your condition.

Yes, Flomax helps reduce the painful spasms of the ureteral smooth muscle, which can decrease the severity of pain associated with ureteral stones. Studies have shown that patients on tamsulosin often require less pain medication.

Flomax is not suitable for everyone. It is not approved for use in women or children. Additionally, those undergoing certain eye surgeries should inform their surgeon, as it can cause complications like Intraoperative Floppy Iris Syndrome. It is important to discuss your medical history with a doctor to determine if it is safe for you.

For best results, take Flomax exactly as prescribed by your healthcare provider. This often involves taking it consistently, potentially after a meal. Swallowing the capsule whole without altering it is important.