Does Metformin Cause Increased Urination? Separating Fact from Fiction

October 10, 2025 •

4 min read

Affecting over 90% of type 2 diabetes patients, metformin is a cornerstone medication, yet a common question is whether it causes frequent urination. This article delves into the science behind how metformin works and clarifies whether does metformin cause increased urination is true, or if other factors are at play.

Quick Summary

Metformin primarily affects blood sugar, not direct diuretic action. Increased urination is often a symptom of uncontrolled high blood sugar or combination medications, not metformin alone. Other factors, like medication excretion, can play a smaller role in urinary changes.

Key Points

Metformin is not a diuretic: It works by reducing glucose production and improving insulin sensitivity, not by directly increasing urine output.
High blood sugar is the main culprit: Frequent urination (polyuria) is a classic symptom of uncontrolled diabetes, which metformin is prescribed to treat.
Excretion is a minor factor: The body excretes metformin unchanged, and this process, especially with higher doses, can involve some fluid loss, though it is not a direct diuretic effect.
Differentiate from SGLT-2 inhibitors: Be aware of the difference between metformin and SGLT-2 inhibitor drugs (e.g., Jardiance), which actively increase urinary glucose and water excretion.
Consider combination drugs: If you take a combination pill containing metformin and an SGLT-2 inhibitor, the increased urination is a side effect of the SGLT-2 component.
Rule out other causes: Urinary tract infections (UTIs) and diabetic neuropathy can also cause frequent urination and should be investigated by a doctor.

Understanding Metformin's Mechanism

Metformin, a member of the biguanide class of medications, is the first-line treatment for type 2 diabetes. Its primary function is to manage blood glucose levels, but it does so through a distinct process that does not involve directly increasing urination. Unlike diuretic medications or newer diabetes drugs, metformin is not considered a diuretic.

Key aspects of metformin's action include:

Decreasing Liver Glucose Production: Metformin reduces the amount of glucose the liver releases into the bloodstream, helping to lower overall blood sugar levels.
Improving Insulin Sensitivity: It helps the body's cells respond more effectively to insulin, enabling better glucose uptake.
Slowing Glucose Absorption: It can slow the absorption of glucose from the digestive tract.

This mechanism differs significantly from drugs that explicitly target the kidneys to increase urine output. Therefore, the common perception that metformin is a diuretic and directly causes polyuria is a misconception.

Metformin vs. Other Diabetes Medications

It is important to distinguish metformin's effects from those of other diabetes medications, particularly the newer class of drugs known as SGLT-2 inhibitors. These medications work very differently, and confusion between them may be a source of the misconception about metformin and urination.

SGLT-2 Inhibitors and Increased Urination

SGLT-2 inhibitors, such as dapagliflozin (Farxiga) and empagliflozin (Jardiance), are designed to lower blood sugar by causing the kidneys to excrete excess glucose through the urine. This process is a direct cause of increased urination and fluid loss. Some combination drugs contain both metformin and an SGLT-2 inhibitor, so patients on these therapies would likely experience increased urination as a direct side effect of the SGLT-2 component.

Comparison of Metformin and SGLT-2 Inhibitors


Feature	Metformin	SGLT-2 Inhibitors
Primary Mechanism	Decreases liver glucose production and improves insulin sensitivity.	Promotes kidney excretion of glucose into the urine.
Effect on Urination	Does not directly cause increased urination; some fluid excretion occurs as the drug is cleared.	Directly causes frequent and increased urination (polyuria).
Primary Side Effects	Gastrointestinal issues like diarrhea, nausea, and abdominal discomfort.	Increased risk of urinary tract and genital yeast infections due to glucose in the urine.
Weight Impact	Often associated with modest weight loss.	Can also cause weight loss by excreting glucose and calories.

Indirect Causes of Urinary Changes While on Metformin

While metformin itself is not a primary cause of frequent urination, several factors related to diabetes and its treatment can lead to changes in urinary habits for patients taking the medication. These are often the true sources of the issue.

Uncontrolled High Blood Sugar (Hyperglycemia): Frequent urination is a classic symptom of high blood sugar. When blood glucose is elevated, the kidneys work overtime to filter and excrete the excess sugar, pulling fluid from body tissues along with it. If a patient is starting metformin or their dose is being adjusted, their blood sugar might still be elevated, causing polyuria. Over time, as metformin effectively lowers blood sugar, urinary frequency should decrease.
Metformin Excretion: Metformin is excreted by the kidneys unchanged and is not metabolized by the body. For the kidneys to flush the medication out of the body, particularly at higher doses, some fluid excretion is involved. While this is not the diuretic-like action of SGLT-2 inhibitors, it could contribute slightly to increased output in some individuals.
Combination Therapies: As mentioned, if metformin is prescribed alongside an SGLT-2 inhibitor or other diuretic medications, the increase in urination is likely a side effect of the other drug(s).
Urinary Tract Infections (UTIs): People with diabetes have a higher risk of developing urinary tract infections. A UTI can cause a frequent and urgent need to urinate, along with other symptoms like pain or burning. If a patient on metformin develops a UTI, the infection—not the medication—is the cause of the urinary symptoms. A large study found no link between metformin use and an increased risk of UTIs.
Diabetic Neuropathy: In the long term, uncontrolled diabetes can cause nerve damage (neuropathy) that affects the nerves controlling the bladder. This can lead to issues with bladder function, including both underactive and overactive bladder symptoms.

How to Address Concerns About Increased Urination

If you are taking metformin and experiencing frequent or difficult urination, it's essential to communicate with your healthcare provider. Here are some strategies that can be explored:

Discuss Your Symptoms: Your doctor can help determine the root cause, whether it's related to blood sugar control, another medication, a UTI, or a different issue.
Optimize Diabetes Management: Better control of blood glucose is often the most effective way to address polyuria related to diabetes.
Consider Extended-Release Metformin: Some patients find that the extended-release (ER) version of metformin causes fewer side effects, including gastrointestinal discomfort, which may affect overall well-being.
Check for UTIs: Since UTIs are common in diabetics, your doctor may perform a urinalysis to check for an infection.
Review All Medications: Ensure your provider reviews your entire medication list to rule out interactions or effects from other drugs.
Timing of Fluid Intake: If nighttime urination (nocturia) is a problem, managing fluid intake, particularly in the evening, may help.
Pelvic Floor Physical Therapy: In cases where underlying bladder issues are identified, pelvic floor physical therapy may be an option for some patients.

Conclusion

Ultimately, the answer to does metformin cause increased urination is that it's an indirect effect, if at all. Metformin is not a diuretic, and the more common causes of frequent urination are either the underlying high blood sugar it treats or another factor entirely, such as a urinary tract infection or a different medication. By working closely with a healthcare provider to achieve good glycemic control and addressing other potential issues, patients can effectively manage their urinary symptoms while continuing their metformin therapy. For more detailed information on managing diabetes and its symptoms, the American Diabetes Association provides comprehensive resources [Link: https://diabetes.org/].

Frequently Asked Questions

While not a direct side effect of metformin itself, it is not uncommon for individuals with poorly controlled diabetes to experience frequent urination due to high blood sugar levels. As metformin helps lower blood sugar, this symptom should decrease over time.

Some individuals report a minor increase in urination, particularly at higher doses of metformin. This is primarily because the kidneys excrete the unmetabolized drug, which involves some fluid clearance.

Increased urination from high blood sugar will typically improve as your blood glucose levels stabilize with metformin treatment. If urination remains a problem despite stable blood sugar, other causes such as an underlying infection should be investigated by your doctor.

Large-scale studies indicate that metformin use does not significantly increase the risk of UTIs. However, diabetes itself can increase UTI risk. If you experience burning or painful urination, consult your doctor.

Many patients find the extended-release (ER) version of metformin causes fewer gastrointestinal side effects. If you are experiencing discomfort, discussing a switch to the ER formulation with your doctor is a good option.

Staying hydrated is important, but if you have high blood sugar, increased fluid intake will lead to more urination. Focus on controlling your blood sugar and timing your fluid intake to avoid nighttime disruptions.

Metformin does not directly cause increased urination. SGLT-2 inhibitors, a different class of diabetes medication, explicitly increase urination by causing the kidneys to flush glucose from the body.