Metformin and Liver Disease: How to Prevent Lactic Acidosis

Metformin is the most common pill prescribed for type 2 diabetes worldwide. Millions take it daily. It’s cheap, effective, and has been around for decades. But if you have liver disease, your doctor might tell you to stop it. Why? Because of a rare but dangerous side effect: lactic acidosis.

What Is Lactic Acidosis, and Why Does Metformin Cause It?

Lactic acidosis happens when too much lactic acid builds up in your blood. Your body normally makes small amounts of lactate during exercise or when oxygen is low. Your liver clears it out. But if your liver is damaged, it can’t do that job well. Metformin makes this worse. It blocks a key energy pathway in your cells, which increases lactate production. At the same time, it reduces how much your liver can turn lactate back into glucose. That double hit can push lactate levels into dangerous territory.

The clinical definition is simple: blood pH below 7.35 and lactate above 5 mmol/L. That’s not something you can feel right away. Symptoms are vague-nausea, vomiting, stomach pain, feeling weak. Many people think it’s just a stomach bug. But if you’re on metformin and your liver isn’t working well, these symptoms could be early warning signs. About 83% of people with metformin-related lactic acidosis end up with dangerously low blood pressure. Nearly half need a breathing machine.

The Old Rule: Avoid Metformin in Liver Disease

Back in 1998, regulators said: don’t use metformin if you have chronic liver disease. That rule stuck. It came from fear, not hard data. At the time, phenformin-a similar drug-had caused hundreds of deaths from lactic acidosis. When metformin came along, doctors assumed it was just as risky. But it’s not. Phenformin was broken down by the liver. Metformin? Over 90% leaves your body through your kidneys. That’s why kidney problems are a bigger red flag than liver problems.

Here’s the twist: people with liver disease often have type 2 diabetes. Studies show about 30% of people with cirrhosis also have diabetes. So if you’re one of them, you need treatment. But if metformin is off the table, what’s left? Insulin? Newer drugs? They work-but they’re more expensive, harder to use, and can cause weight gain or low blood sugar.

The New Evidence: Metformin Might Be Safe-Sometimes

In 2024, a major case report in Cureus reviewed the data and found almost nothing to support the blanket ban. Most reports of lactic acidosis in liver patients involved people who were also drinking heavily, had kidney failure, or were taking other drugs. The real risk isn’t the liver disease alone-it’s when liver disease is paired with other problems.

What about non-alcoholic fatty liver disease (NAFLD)? That’s the most common liver condition in people with diabetes. It’s not the same as cirrhosis. In fact, metformin may actually help NAFLD. It reduces fat in the liver, improves insulin sensitivity, and lowers inflammation. A 2022 study showed that patients with NAFLD and diabetes who stayed on metformin had slower disease progression than those who stopped.

The American Diabetes Association updated its 2023 guidelines to say metformin is okay for patients with stable chronic liver disease-even compensated cirrhosis (Child-Pugh Class A). That’s a big shift. It means if your liver is damaged but still working, metformin might be safe. The European Association for the Study of the Liver is preparing new guidelines for 2025 that could go even further, recommending metformin as first-line therapy for NAFLD with diabetes.

When Is Metformin Still Dangerous?

Not all liver disease is the same. If you have decompensated cirrhosis-meaning your liver is failing-you’re at high risk. That’s Child-Pugh Class B or C. Your body can’t clear lactate. Your blood pressure drops. Your organs start shutting down. In these cases, the mortality rate from lactic acidosis is 28% to 47%. No one should take metformin here.

Other red flags:

• Severe kidney problems (eGFR under 30)
• Acute illness with dehydration (like severe diarrhea or infection)
• Heart failure requiring hospitalization
• Alcohol abuse
• Recent contrast dye scan (like a CT scan with contrast)

These aren’t just warnings-they’re triggers to stop metformin immediately. Even if your liver is fine, if your kidneys are struggling or you’re dehydrated, lactate can pile up fast.

How to Use Metformin Safely With Liver Disease

If your doctor says you can stay on metformin, here’s how to do it safely:

1. Get your liver function tested every 3 months. Look at ALT, AST, bilirubin, and albumin. If they’re stable, you’re probably okay.
2. Check your kidney function every 6 months. eGFR above 45 is ideal. Between 30 and 45? Your dose may need lowering.
3. Never skip meals. Fasting increases lactate. If you’re sick and can’t eat, stop metformin until you’re eating normally again.
4. Stop metformin 48 hours before any surgery or imaging with contrast dye. Wait until you’re fully recovered and drinking fluids before restarting.
5. Watch for symptoms: nausea, vomiting, unusual tiredness, muscle pain, rapid breathing. If you have them, get a lactate test right away.

Some doctors now check lactate levels every 6 months in high-risk patients, even if they feel fine. It’s not routine-but it’s smart if you have cirrhosis or NAFLD with diabetes.

What If You’re Already on Metformin and Have Liver Disease?

Don’t panic. Don’t quit cold turkey. Talk to your doctor. Ask:

• What stage is my liver disease? (Child-Pugh Class A, B, or C?)
• Are my kidneys working well?
• Do I have other risk factors like alcohol use or heart failure?
• Has my diabetes been stable on metformin?

If your liver is mildly affected and everything else is stable, you’re likely fine. Many people with NAFLD have been on metformin for years without issue. The real danger isn’t the drug-it’s the fear of it. Studies like the UKPDS followed patients for 10 years and found zero cases of lactic acidosis in those taking metformin. The COSMIC trial with over 7,000 patients also found no cases.

The data doesn’t support a blanket ban. It supports smart, individualized care.

What Are the Alternatives?

If metformin isn’t safe for you, here are your options:

• Insulin: Works well, but can cause weight gain and low blood sugar.
• GLP-1 agonists (like semaglutide): Help with weight loss and liver fat reduction. Expensive, but very effective.
• SGLT2 inhibitors (like empagliflozin): Lower blood sugar and protect the heart and kidneys. May also reduce liver fat.
• DPP-4 inhibitors (like sitagliptin): Neutral for weight, low risk of low sugar. Safe in liver disease.

None of these are perfect. But they’re options. The goal isn’t just to lower blood sugar-it’s to protect your liver, heart, and kidneys too.

The Bottom Line

Metformin isn’t automatically dangerous if you have liver disease. The old rule is outdated. The real risk is in advanced liver failure-not fatty liver or mild cirrhosis. If you’re on metformin and have liver disease, get your liver and kidney function checked regularly. If you feel unwell, get your lactate tested. Don’t stop your medication without talking to your doctor.

The future of diabetes care in liver disease isn’t about avoiding metformin. It’s about using it wisely. And that starts with knowing your numbers-not your fears.

What’s Next?

If you have diabetes and liver disease, your treatment plan should be personal. Don’t assume metformin is off-limits. Don’t assume it’s safe without checking. Ask for your liver and kidney numbers. Know your Child-Pugh class if you have cirrhosis. Track your symptoms. And if you’re unsure-get a second opinion from an endocrinologist or hepatologist.

The goal isn’t to avoid all risk. It’s to manage it. Metformin saves lives. But only if it’s used the right way.