Is Metformin Bad for You? 4 Facts to Know About Cancer, Kidney, and Liver Damage Risks
Key takeaways:
In 2020, some extended-release (ER) metformin products were found to contain high levels of the chemical N-nitrosodimethylamine (NDMA). As a result, some ER metformin products were recalled.
Metformin itself isn’t known to cause cancer. Even if your metformin was recalled, don’t stop taking it before talking with your healthcare provider.
Metformin isn’t known to damage your kidneys or liver. But you need healthy kidneys to clear metformin from your body. Your healthcare provider may monitor you more closely if you have existing kidney or liver problems.
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Table of contents
Metformin is one of the most prescribed medications in the U.S. It’s a first-choice medication for people with Type 2 diabetes. It’s also the medication of choice to help treat prediabetes. Common side effects of metformin are usually stomach related and include diarrhea, nausea, and gas.
But past FDA recalls of metformin caused concern for millions of people. It left many wondering if metformin causes cancer. Below, we’ll address four common concerns and separate fact from fiction.
1. Does metformin cause cancer?
No. Metformin itself is not known to cause cancer.
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In fact, it might help prevent cancer. People with Type 2 diabetes have a higher risk for some types of cancer, including pancreatic, breast, and endometrial cancers. But some studies suggest that metformin may lower the risk of developing cancer.
Still, hearing that some extended-release (ER) metformin products were recalled can be worrying. These products were recalled due to the presence of a potentially harmful chemical called N-nitrosodimethylamine (NDMA). NDMA may raise your risk of cancer if you take large amounts for a long time. This is true for any product with high levels of NDMA, not just metformin.
What is NDMA?
NDMA is a type of nitrosamine. Nitrosamines naturally exist at low levels in our food and water. And low levels are actually allowed in our medications. NDMA isn’t intentionally added to medications, but chemical reactions that take place during the manufacturing process can cause NDMA to end up in the final product.
But, as discussed above, too much NDMA can be dangerous and may raise your risk of cancer if consumed over a long period of time.
2. Does metformin cause liver damage?
No. Metformin isn’t known to damage your liver. Your liver isn’t involved in processing metformin. Even in people with liver issues, metformin is usually considered safe.
Still, there are warnings on metformin’s prescription labeling about liver damage. Liver damage (like liver cirrhosis) can make you more likely to experience lactic acidosis. This is where lactic acid builds up in your blood. It can lead to health problems that can be life threatening. Since metformin can make lactic acidosis more likely, let your healthcare provider know if you have any liver issues before starting metformin.
Your healthcare provider may recommend blood work to check the function of your liver. But, even if you have existing liver damage, it doesn’t mean you can’t take metformin. Talk to your healthcare provider about the risks and benefits of taking metformin if you have liver problems.
3. Can metformin cause kidney damage?
No. Metformin isn’t known to cause kidney problems in people with healthy kidneys. But if your kidney function is significantly lower than normal, metformin may not be the best choice for you.
Metformin is removed from your body through your kidneys. If your kidneys aren’t working normally, they may not be able to get rid of metformin as effectively. This puts you at risk for lactic acidosis.
If you have moderate to severe chronic kidney disease, metformin may not be the best option for you. Before starting metformin and during treatment, your healthcare provider should check how well your kidneys are working by asking you to complete blood work. This helps your healthcare provider decide what the best dose of metformin is for you.
If you take metformin, you may need to stop it for a short time in situations where your kidney function is lowered temporarily. This may include medical procedures where you need intravenous (IV) contrast.
4. Why did the FDA recall metformin?
In 2019, the FDA learned that metformin was recalled in other countries due to the presence of NDMA. As a result, some — but not all — metformin ER products were recalled.
If you were taking one of the recalled products, it's difficult to know exactly how long you were exposed to higher than normal levels of NDMA. But the FDA doesn’t think that short-term exposure to NDMA in recalled metformin raises your cancer risk. The FDA and other international agencies decide what levels of NDMA are safe. This is called the acceptable intake limit. If a medication contains NDMA levels above this limit, it’s considered potentially unsafe.
After the FDA learned that other countries were recalling some forms of metformin, it began testing U.S. metformin products. The FDA found levels of NDMA above the acceptable intake limit in some metformin ER products. This led to voluntary recalls by the manufacturers of these products.
It’s important to know that NDMA hasn’t been found in any immediate-release (IR) metformin tablets. At the time this article was last updated, no metformin IR products have been recalled.
How do you know if your metformin was recalled?
There are many ways that you might hear about a medication recall, including:
In the news: Often, recalls are broadcasted on television and in online articles. This is especially true for popular products like metformin.
From your pharmacy: Your pharmacy should contact you if your specific medication has been recalled. You can also contact your pharmacy if you aren’t sure if your specific product has been recalled. They’ll be able to tell you if your recent refill is one of the affected products.
On the FDA website: If the FDA recommends a recall, it will list it on its website. But, it’s possible that a recall won’t be posted on the FDA’s website if a manufacturer initiates a recall independently — meaning it wasn’t recommended by the FDA.
On the MedWatch website: The FDA MedWatch program provides a way for the public to report adverse events from medications. After the FDA reviews this information, it may publish safety alerts. Often, this includes information on recalls.
Should you stop taking your metformin after a recall?
Not all metformin ER products were affected by recalls. If you have diabetes, it may be harmful to stop metformin without a replacement medication.
Even if your metformin product was recalled, don’t stop taking it before talking with your healthcare provider. Your healthcare provider and pharmacist can help you decide what replacement options are best for you.
The bottom line
Metformin is considered a safe medication. It isn’t known to cause cancer. Still, some metformin products were recalled in the past few years because of the presence of a chemical called NDMA. Consuming high levels of NDMA over time may be linked to cancer. We don’t know exactly what amount of NDMA you’d have to be exposed to, or how long you’d have to be exposed, for there to be a serious risk.
Metformin isn’t known to cause liver or kidney damage. But if you have known kidney or liver problems, make sure to tell your healthcare provider. They’ll probably ask you to do blood tests to check your kidney and liver function before and during treatment. If your kidneys are significantly damaged, you may need a lower dose of metformin or another medication altogether.
If you take a metformin product that was recalled, you may need to switch to another metformin product or another diabetes medication. It’s important that you don’t stop taking metformin without talking to your healthcare provider first, even if your product was recalled.
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References
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U.S. Food and Drug Administration. (2020). What to know and do about possible nitrosamines in your medication.
U.S. Food and Drug Administration Center for Drug Evaluation and Research. (2021). Control of nitrosamine impurities in human drugs: Guidance for industry. U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (2021). FDA updates and press announcements on NDMA in metformin.
U.S. Food and Drug Administration. (2022). Search list of recalled metformin products.
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