Does Metformin Contain a Cancer-Causing Chemical?

Does Metformin Contain a Cancer-Causing Chemical?

Metformin, a drug that is widely used as a first-line treatment for type 2 diabetes has come under some scrutiny this week, as numerous reports brought forward a concern of contamination with a known carcinogen, NDMA.

Articles like this one and this one highlighted the issue following the recent FDA announcement about investigating the drug for the contaminant.

What is NDMA?

NDMA (N-Nitrosodimethylamine) belongs to the category of nitrosamines, which are found widely in a variety of foods and products in low amounts. According to the CDC, NDMA is, in fact, an established cancer-causing toxin that is “unintentionally formed during various manufacturing processes”. According to the CDC report, the toxic and carcinogenic properties of this chemical are well-established in animal models and “it is reasonable to expect that exposure to NDMA by eating, drinking, or breathing could cause cancer in humans”.

The FDA Statement

According to the official statement from the director of the FDA’s Center for Drug Evaluation and Research, Dr. Janet Woodcock, the organization is currently investigating the potential issue of NDMA contamination in metformin products. This effort followed the identification of the chemical in metformin formulations outside the United States. The FDA is now examining whether NDMA levels in metformin products on the U.S. market are in compliance with the established acceptable level of NDMA contamination.

At this time, it appears that there is no evidence of NDMA levels that exceed the trace amounts deemed acceptable. The FDA press release reminded the public that the investigation was ongoing as a precaution and that while a high level of NDMA exposure is concerning, some level of NDMA exposure is inevitable in our world and is not expected to have negative health consequences at the typically low exposure doses:

“NDMA is a common contaminant found in water and foods including cured and grilled meats, dairy products and vegetables. Everyone is exposed to some level of NDMA. The FDA and the international scientific community do not expect it to cause harm when ingested at low levels. The acceptable daily intake limit for NDMA in the U.S. is 96 nanograms. Genotoxic substances such as NDMA may increase the risk of cancer if people are exposed to them above acceptable levels and over long periods of time, but a person taking a drug that contains NDMA at-or-below the acceptable daily intake limit every day for 70 years is not expected to have an increased risk of cancer.”

Metformin Safety and Cancer

Interestingly, metformin has one of the longest use histories and most well-established clinical safety profiles of all type 2 diabetes drugs. Moreover, it has shown, time and time again, unexpected health benefits outside of glycemic management.

For example, the drug has been shown to have positive effects on longevity, and can have protective effects against “cancer, inflammation and age-related pathologies”. In fact, even more evidence of this was announced just recently.

Almost ironically, when it comes to cancer specifically, a recent publication in Oncology Letters even touted metformin as “an existing drug for cancer prevention and therapy.”

Experts explain:

“Epidemiological and basic studies have demonstrated that [metformin] may also inhibit the growth of a variety of tumor cells, and an increasing number of ongoing clinical trials on the antitumor activity of metformin are being processed for the treatment of cancer. Metformin has been proven to be safe as a treatment drug for T2DM and has subsequently been used clinically for a number of years. If large-scale clinical trials are able to attest to the antitumor effects of metformin, this drug may become an alternative cancer adjuvant therapy, providing a novel approach for cancer prevention and treatment.”


This isn’t the first time in recent history that the FDA has been investigating NDMA levels in our drugs. Earlier this year, the organization issued multiple statements about NDMA contamination of the popular heartburn drug, Zantac (ranitidine), including reports of voluntary recalls from several manufacturers. To date, this investigation is also still ongoing, and it would not be surprising if other drugs also come under evaluation for NDMA levels in the future.

As far as metformin goes, at this time, there is no evidence of any danger to the public, as no harmful levels of NDMA have been detected in any metformin products. The FDA currently recommends no changes in metformin use or prescription for the management of diabetes but will continue to update if new concerning information arises.

“These investigations take time. The FDA will communicate any information we have scientifically confirmed to ensure the public knows as much as possible as soon as possible.”

We will continue to keep you posted on any updates on this matter as more details are announced.

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Read more about cancer, diabetes management, diabetes news, Intensive management, metformin (Glucophage), U.S. Food & Drug Administration (FDA).

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