Living with kidney disease often means managing other health challenges at the same time. One of the most common is type 2 diabetes, a leading cause of kidney problems worldwide. If you live with both, your doctor may have prescribed metformin, a medication long trusted to manage blood sugar. But what if your kidneys aren’t working well?

This article explains how metformin works, how it affects the kidneys, and what doctors consider when deciding whether it’s safe to take.

What Is Metformin and How Does It Help?

Metformin is a pill that helps control blood sugar in people with type 2 diabetes. It has been around for decades, is usually inexpensive, and is often the first-line medicine prescribed after diagnosis. Metformin helps manage blood sugar by:

• Reducing the liver’s production of glucose (sugar)
• Improving the body’s sensitivity to insulin
• Decreasing how much sugar is absorbed from food

Unlike some other diabetes medications, metformin doesn’t usually cause weight gain or hypoglycemia (low blood sugar). These qualities make it popular and widely used around the world.

The Link Between Diabetes and Kidney Disease

High blood sugar over time can damage the tiny blood vessels in the kidneys. This damage leads to chronic kidney disease (CKD), which means your kidneys slowly lose their ability to clean your blood.

That’s why controlling blood sugar is especially important for people with CKD. Metformin helps do just that, but because the kidneys remove metformin from the body, using it when kidney function is too low can lead to problems.

Doctors must balance the benefits of metformin with the risks, especially in people with more advanced kidney disease.

When Is Metformin Safe To Use?

To find out whether metformin is safe, doctors check a number called eGFR, which is short for estimated glomerular filtration rate. It tells you how well your kidneys are working. Here’s how eGFR guides metformin use:

• If your eGFR is above 45, metformin is generally safe.
• If your eGFR is between 30 and 44, it may still be used at a lower dose, but doctors will monitor you closely.
• If your eGFR is below 30, doctors may not recommend metformin.

To obtain the estimated glomerular filtration rate, you will need a blood test to measure a chemical compound called creatinine. Doctors estimate your GFR based on your age, sex, and how much creatinine is in your blood.

This approach helps answer an important concern: When should metformin be stopped in CKD? The answer depends on your kidney function numbers, your symptoms, and your overall health picture.

What Are The Side Effects and Risks of Metformin?

In people with severely reduced kidney function, metformin can build up in the blood. This can cause lactic acidosis, a rare but serious condition where too much lactic acid enters the bloodstream. Although it’s uncommon, it can be life-threatening if not treated quickly. Signs of lactic acidosis may include:

• Muscle pain or weakness
• Feeling unusually tired
• Trouble breathing
• Nausea or stomach pain
• Slow heartbeat
• Feeling cold or lightheaded

If you’re taking metformin and experience these symptoms — especially if your kidney disease is progressing — call your doctor or seek help immediately.

Doctors may also temporarily pause metformin use before medical procedures that use contrast dye (like CT scans or angiograms), which can affect the kidneys.

Can Metformin Damage the Kidneys?

No. Metformin itself doesn’t damage your kidneys. It’s not a toxic drug. But if your kidneys aren’t working well and can’t clear the drug from your system, you can experience serious side effects.

This is a key difference. The problem isn’t that metformin causes kidney damage. The concern is that poor kidney function increases the risk of lactic acidosis if metformin isn’t cleared properly.

So, can metformin damage your kidneys? The answer is no, but it can be too risky to use if your kidneys are already damaged.

Staying Safe: What To Watch For

If you’re taking metformin and have any form of kidney disease, here are some safety tips:

• Get regular blood tests. Your healthcare team should check your creatinine levels every three to six months.
• Watch for side effects, especially signs of lactic acidosis.
• Check vitamin B12 levels periodically, because long-term use of metformin can cause low vitamin B12.
• Tell your doctor about all medications you’re taking, since some drugs can affect kidney function.
• Ask your doctor about pausing metformin use for 48 hours before and after any procedures involving contrast dye.

The good news? According to the U.S. Food and Drug Administration (FDA), with proper monitoring, many people with CKD can safely take metformin for years.

If You Can’t Take Metformin, What Are the Options?

Some people may wonder why doctors aren’t prescribing metformin as often. It’s not because the medicine is bad. It’s because for some people, the risks of lactic acidosis now outweigh the benefits. If you need to stop taking metformin, your doctors may suggest one of the following alternatives. There’s no one-size-fits-all plan. Your doctor will choose what’s best for your health needs and lab results.

• SGLT-2 inhibitors — These medications lower blood sugar and protect the kidneys.
• Glucagon-like peptide 1 receptor agonists — These medications lower blood sugar and also support weight loss.
• Insulin therapy — This treatment can be customized based on blood sugar and kidney function, which makes it a great option for those with progressing kidney disease.

What To Ask Your Doctor

Managing multiple conditions can be overwhelming. Here are a few helpful questions to ask your care team:

• Is my kidney function still in the safe range for metformin?
• How often should we check my eGFR and B12?
• Are there signs I should watch for that mean it’s time to stop?
• Are there other diabetes medicines I should consider?

Your treatment should be tailored to your unique situation. Blood tests, open communication with your care team, and awareness of symptoms can help prevent complications and keep you feeling your best.

Talk With Others Who Understand

On MyKidneyDiseaseTeam, the social network for people with kidney disease and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with kidney disease.

Do you have both diabetes and kidney disease? Have you been prescribed metformin? Share your experience in the comments below, or start a conversation by posting on your Activities page.