The U.S. Food and Drug Administration is investigating whether the diabetes drug metformin contains unsafe levels of a carcinogen. This investigation follows recalls of the drug outside of the U.S. (1)

Testing Metformin for NDMA

In a statement released on December 5, 2019, the FDA announced that it would be testing samples of metformin for a nitrosamine called N-Nitrosodimethylamine (NDMA). Nitrosamines are chemical compounds, and most are carcinogenic. Previously, NDMA has been found in medications for heart and gastric conditions. (1, 2, 3)

Doctors commonly prescribe metformin when patients are first diagnosed with type 2 diabetes. For people who have type 2 diabetes, the body either resists the effects of insulin or doesn’t make enough. On their website, the FDA cautioned patients with type 2 diabetes to continue to take metformin as prescribed. They warned that stopping medication without talking to a doctor could be dangerous. The FDA pointed out that their investigation of the drug is ongoing and that there isn’t an alternative for metformin that treats type 2 diabetes in the same way. (2, 4)

Drug Recalls

The FDA’s investigation into metformin comes after Singapore health officials pulled 3 of the 46 versions of the drug sold in the country. In a statement, Singapore’s Health Sciences Authority said that they had found levels of NDMA “above the internationally acceptable level.” (1, 5)

Bloomberg reported that the European Medicines Agency (EMA) advised companies to test for high levels of NDMA in metformin. “Although the risk from NDMA seen so far has been very low, impurities such as NDMA should be avoided in medicines,” the EMA said in an email to Bloomberg. “If NDMA is found above a certain level, authorities will take necessary action.” (1)

NDMA in Metformin

According to the FDA, NDMA is a common contaminant. It is found in water and many foods, including vegetables, dairy products, and grilled and cured meats. At a low level, it is safe to ingest NDMA. (2)

In the U.S., the acceptable daily intake limit for NDMA is 96 nanograms. The FDA says that a person who ingests NDMA at or below the acceptable daily intake limit for 70 years would likely not have an increased risk for cancer. However, if people have exposure to the substance that is higher than the acceptable levels over longer periods of time, their risk for cancer could increase. This is why the FDA is investigating drugs like metformin that contain NDMA. (2)

The FDA has access to technology and testing methods that allow them to investigate the chemical structure of drugs, as well as their manufacturing processes. They are able to find tiny amounts of impurities. The agency also works with international drug regulatory agencies to learn about testing done outside of the U.S. This information alerts the FDA to possible issues with drugs sold within the U.S. (2)

In their statement, the FDA warned that the investigation would take time. They promised to provide Americans with as much clarity as possible regarding NDMA in metformin. They wrote, “The American public can expect that we will act quickly to address any issue as soon as we find out about it.” (2)