Metformin and liver health: Risks, benefits, and safety

In this article:

• Is metformin bad for your liver? 
• Benefits of metformin on the liver
• Safety and risks of metformin on the liver
• The bottom line

In this article

• Is metformin bad for your liver? 
• Benefits of metformin on the liver
• Safety and risks of metformin on the liver
• The bottom line

Diabetes is one of the most common diseases in the U.S., and metformin (brand name: Fortamet, Glumetza) is the most commonly prescribed diabetes medication. An estimated 19 million Americans took it in 2022 to help control blood glucose levels. But because it tells the liver to reduce its glucose production, many people wonder if it affects the liver in other ways. While it might cause liver complications in very rare cases and in people with cirrhosis, it can also benefit people with certain liver diseases. We’ve got all the details below. 

Is metformin bad for your liver? 

Metformin isn’t inherently harmful to the liver, although it does affect liver function. A ​​biguanide drug, it inhibits a process called gluconeogenesis, which is how the liver turns things like amino acids and lactate into glucose. This lowers the body’s blood sugar, a key component of treating diabetes mellitus. 

Even though it changes how your liver functions, metformin shouldn’t wear the organ down. Most metformin users can take the medication long term without experiencing harmful hepatic effects. But like most drugs, there’s a slight risk of serious side effects—and that includes ones involving the liver. 

“Metformin is generally safe for the liver, but in rare cases, it may cause liver problems, especially in people with pre-existing liver disease,” says Dr. Yoshua Quinones, MD, board-certified internist with Medical Offices of Manhattan and contributor to https://www.labfinder.com. “It can sometimes lead to a buildup of lactic acid in the blood, known as lactic acidosis, which can harm the liver.”

Additionally, certain case studies have shown that the use of metformin may cause liver injury (hepatotoxicity). Others have suggested that it might cause intrahepatic cholestasis—a condition that reduces or blocks bile as it flows out of the liver. These adverse effects of metformin are extremely rare, but if you experience jaundice, fatigue, anorexia, pruritus, and dark urine while taking metformin, seek medical attention. 

Benefits of metformin on the liver

Not only is metformin therapy relatively liver-safe for most people, but it might actually help improve your liver health. Here’s how it might benefit people with certain conditions. 

Non-alcoholic fatty liver disease (NAFLD)

“Metformin helps reduce fat accumulation in the liver by improving insulin sensitivity,” according to Dr. David Garcia, DO, founder of Polaris Rejuvenation. “This is beneficial in conditions like non-alcoholic fatty liver disease, where excess fat builds up in liver cells.”

As the name suggests, non-alcoholic fatty liver disease is a condition that causes lipid accumulation in the liver, unrelated to alcohol consumption. It’s the most common chronic liver disease, and certain recent studies—like this one from 2021 and this one from 2022—demonstrate the efficacy of metformin for the treatment of NAFLD. 

“People with fatty liver disease often have elevated liver enzymes, indicating liver stress or damage. Metformin has been shown to help normalize these enzyme levels,” Dr. Garcia says. Some research has associated the medication with lower levels of alanine aminotransferase (ALT). 

Hepatitis C

Hepatitis C is an inflammatory condition of the liver caused by the Hepatitis C virus (HCV). It can be a short-term or chronic illness, and when left untreated, it can cause serious liver damage, liver failure, or liver cancer. 

Cirrhosis

This is when scar tissue in the liver—from hepatitis, alcoholism, or other liver diseases—prevents it from functioning properly. In some cases, metformin may improve the rates of mortality and hepatic complications. One study even found that it reduced the risk of death in patients with diabetes and cirrhosis by 57%. Per Dr. Garcia, “In some studies, metformin has been suggested to slow or prevent the progression of fibrosis (scarring) in the liver, which can lead to cirrhosis if left untreated.”

But doctors are careful in prescribing it to patients with cirrhosis since it can cause some serious issues in patients with reduced liver function (see below). 

Liver Cancer

Research suggests that long-term metformin use might reduce the risk of liver cancer in people with Type 2 diabetes and chronic liver diseases. For example, results from a 2018 study demonstrated “a strong inverse association between metformin and liver cancer,” and a systematic review and meta-analysis from 2016 found a significant improvement in survival rates for diabetic liver cancer patients. 

Safety and risks of metformin on the liver

For diabetic patients with otherwise healthy livers, metformin shouldn’t present any serious issues. But as Dr. Quinones mentions, it’s been linked to lactic acidosis in patients with pre-existing liver or kidney impairment. 

This is when lactic acid builds up in the bloodstream because your kidneys and liver can’t eliminate it fast enough. In mild cases (like those caused by strenuous exercise), but when lactic acid continues accumulating because of liver or kidney impairment, it can lead to organ failure and even death. It’s rare, but serious enough that the FDA has included a warning on the label for people who have reduced kidney or liver function. 

The typical metformin dosage to treat Type 2 diabetes in adults is 500–1000 mg twice per day. The daily dosage shouldn’t exceed 2550 mg. People with renal or hepatic impairment should generally avoid metformin altogether, although one study suggests that doctors might reduce the daily maximum dose to 1500 mg, and potentially further. 

“Patients with pre-existing liver conditions who are using metformin should take precautions, such as regularly monitoring liver function through blood tests and watching for symptoms like fatigue or jaundice—a condition in which the skin, the whites of the eyes, and mucous membranes turn yellow,” Dr. Quinones says. “It’s also important to avoid alcohol, as it can increase the risk of liver damage and lactic acidosis.”

He continues: “Patients taking metformin usually do not need regular liver function tests unless they have existing liver conditions. For those with a history of liver disease, testing is typically recommended every three to six months.” It all depends on your specific condition and circumstances. 

The bottom line

Most of the time, metformin is a liver-friendly medication. There’s a slim chance that it may cause liver damage, but these cases are the exception, not the rule. Even so, it’s crucial to consult your doctor before taking metformin, and be open with them about your health history, lifestyle, and preferences. That way, they can tailor your metformin treatment to your specific condition. If you have existing liver issues, your healthcare provider may steer clear of metformin and recommend another drug instead. If not, they may say you and your liver are good to go.