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# FDA Now Worried About Metformin Containing Carcinogen
- URL: https://www.fdaweb.com/fda-now-worried-about-metformin-containing-carcinogen/
- Published: 2020-05-28T12:00:00.000Z
- Updated: 2026-09-14T16:16:18.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5146882

As part of its ongoing testing and investigation into high levels of a possible cancer-causing impurity in some marketed drugs, FDA has added diabetes drug metformin to its watch list of drugs with potential safety concerns. The agency says it is notifying companies whose drugs had N-nitrosodimethylamine (NDMA) over accepted levels and it will take appropriate action.

FDA’s acknowledgment of the NDMA detection follows a [5/27 report](https://www.valisure.com/blog/valisure-news/study-of-crowdsourced-metformin-tablets-from-individuals-reveals-widespread-ndma-contamination/?ref=fdaweb.com) from Valisure about its testing of crowdsourced metformin samples sent directly from individuals around the U.S. to Valisure’s laboratory. Previously, FDA posted lab results, which evaluated metformin tablets from seven companies and 16 batches, finding that all passed its daily acceptable intake limit for NDMA. “However, the FDA may have acquired the drug or medication samples through voluntary submission, which can introduce significant sampling bias,” Valisure said.

According to Valisure, “42% of all medication samples contained detectable levels of NDMA and, when scaled to maximum daily tablet dose, 36% of all medication samples contained NDMA levels exceeding the FDA daily acceptable intake limit. The highest NDMA detection from the tested samples was 1,565 ng per tablet, which, when commonly taken four times a day, is 65 times the United States Food and Drug Administration (FDA) acceptable daily intake limit. Results underscore the need for immediate product recalls of tainted medications and an overall investigation of metformin manufacturing practices.”

An FDA spokesperson told Bloomberg News that the agency cannot comment on any pending recall action.