Several companies have initiated recalls of metformin extended-release (ER) tablets due to the possibility of unacceptable levels of N-Nitrosodimethylamine (NDMA), a probable human carcinogen.

The Food and Drug Administration (FDA) has published a recalled metformin list that includes the NDC Number, Lot Number, and Expiration Date for all affected products. According to the Agency, patients who take a drug that contains nitrosamine impurities at or below acceptable daily intake levels are not expected to be at an increased risk of cancer, even if the drug is ingested daily for 70 years. However, the risk may be increased in individuals who are exposed to these genotoxic substances above acceptable levels and for long periods of time.

Metformin, a biguanide, is indicated to improve glycemic control in patients with type 2 diabetes, as an adjunct to diet and exercise. At this time, the Agency recommends healthcare professionals continue to prescribe metformin when clinically indicated. Patients should also continue taking metformin ER until advised by their healthcare provider about an alternative treatment option. The immediate-release formulation of metformin has not been found to contain NDMA based on FDA testing. 

Additionally, the Agency has updated laboratory results for tested metformin products, which can be found here. The Agency is requesting that all manufacturers of metformin ER test their products for NDMA before releasing it into the US market. 

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A recent study published in the American Association of Pharmaceutical Scientists Journal illustrates the importance of selection and validation of testing methods for NDMA. The paper reported that a private laboratory method for testing metformin was found to be inappropriate for quantifying NDMA. The private lab reported levels of NDMA above the acceptable intake limit more often than what was found in the FDA assessment. According to the Agency, this was due to the presence of a substance that interfered with the private labs testing results. 

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