The 2020 metformin recalls and the NDMA found in extended-release tablets

On May 28, 2020, the Food and Drug Administration said its own laboratory had found N-nitrosodimethylamine, or NDMA, above the acceptable intake limit in some lots of extended-release metformin, and that it had contacted five manufacturers to recommend recalls. Two weeks later the agency named the products: all lots from two makers, 14 lots from a third and single lots from two others, according to FDA's running log of metformin announcements¹.

Metformin is one of the most widely used diabetes drugs in the country, and the extended-release (ER) version is taken once a day. The recalls never touched the immediate-release (IR) tablets that make up most prescriptions. FDA said in its question-and-answer page⁴ that it had detected NDMA above the limit only in some ER products, "but not in any tested immediate release metformin."

The episode was the third major nitrosamine case in two years, after the blood pressure drugs called ARBs and the heartburn drug ranitidine. It also turned on a fight over lab methods that is still instructive for anyone reading a contamination headline.

A problem first reported outside the US

Word of the problem reached FDA from abroad. On Dec. 5, 2019, Janet Woodcock, then director of the Center for Drug Evaluation and Research, said in a statement² that some metformin sold in other countries had been reported to contain low levels of NDMA and that "there are no metformin recalls affecting the U.S. market at this time." She said FDA would test US products against an acceptable daily intake limit of 96 nanograms.

That limit comes from lifetime cancer-risk math. FDA's metformin testing page³ explains that a person taking a drug with NDMA at or below 96 nanograms a day every day for 70 years "is not expected to have an increased risk of cancer." NDMA also turns up in water and in foods such as cured and grilled meats, which is why the agency talks about an acceptable level rather than zero. GxRadar's earlier piece on nitrosamine impurities covers how these limits were set after the 2018 valsartan recall.

What FDA's testing found

On Feb. 3, 2020, FDA posted its first metformin results and said levels ranged "from not detectable to low levels," with no sample over the limit, according to the agency log¹. That changed in late May, when ER lots began failing.

In its final form, last updated June 5, 2020, FDA's results table³ lists 37 product and strength combinations: 13 immediate-release and 24 extended-release. Twelve of the 24 ER listings had a measurable amount of NDMA. The highest reading was 0.19 micrograms per tablet in one maker's 500 mg ER lots, which works out to 190 nanograms, roughly twice the daily limit in a single tablet. One 850 mg IR product showed 0.01 micrograms; the other IR listings were "not detected."

There was also a dispute over numbers. A private testing laboratory had told FDA in a citizen petition that 16 of 38 metformin products it tested were above the limit. FDA scientists retested the same 38 samples and found only eight over the limit, according to a paper they published in the AAPS Journal in July 2020⁶. They traced the gap to a common solvent, dimethylformamide, which can be mistaken for NDMA in mass spectrometry unless the instrument settings are tight enough. FDA's summary on its update page¹ called the private method "inappropriate for quantifying NDMA in metformin drug products."

Nowhere on these pages did FDA pin down where the impurity came from. FDA said it did "not believe the metformin active pharmaceutical ingredient is a primary source of NDMA," and that it did not have evidence to determine how long NDMA had been present, in the Q&A⁴.

How the recalls unfolded

Dates in the timeline below come from FDA's announcement log¹.

The June 11 step mattered more than any single recall. FDA asked every company making ER metformin to evaluate its risk and test at-risk product before each batch reached the US market. If testing showed NDMA above the limit, the company "must inform the agency and should not release the batch," the Q&A⁴ says.

Supply was a live concern. FDA noted that other manufacturers that "supply the bulk of the US market" were not recalling, and said it would work with companies to prevent or reduce shortages. Throughout, the agency's notices told patients not to stop metformin on their own and to talk with a doctor or pharmacist first, warning that stopping without guidance "could be dangerous" for people with type 2 diabetes. FDA kept a searchable list of recalled metformin products⁵ by NDC and lot.

What the recall records show

GxRadar searched FDA's openFDA enforcement database⁹ for metformin products whose recall reason cites NDMA or nitrosamines. The search returned 47 records, from 27 separate recall events by 17 recalling firms, a group that includes repackagers who relabel another company's tablets. Every record was voluntary and every one was classed Class II, the middle tier that FDA uses when a product may cause temporary or medically reversible harm. (Our explainer on how drug recalls work covers the three classes.)

Those records cover tablets in 500 mg, 750 mg and 1,000 mg strengths and one oral suspension. Their stated quantities vary widely; the single largest record listed about 1.59 million bottles of 500 mg tablets. The last record in the database was initiated on Feb. 22, 2023, for a 1,000 mg ER product, which suggests batch testing continued to catch occasional failures well after the 2020 wave.

Metformin was one part of a broader spike. In GxRadar's tally of FDA recall records on our recalls page, the category for impurities such as nitrosamines held 58 records in 2017, 168 in 2018, 215 in 2019 and 137 in 2020.

Prices for the common IR tablet barely moved, as GxRadar's metformin price history shows in full. GxRadar's analysis of CMS NADAC files¹¹ shows pharmacies paid an average of about 1.55 cents per metformin 500 mg tablet in December 2019 and about 1.67 cents in June 2020, the month the recalls were named. By October 2026 it was 1.47 cents. NADAC does not track the ER form in our data set, so these figures say nothing about ER prices.

Where things stand

Since then, the lessons have been folded into a wider rulebook. In September 2024 FDA issued a revised guidance, Control of Nitrosamine Impurities in Human Drugs⁷, which sets out how manufacturers should assess and test for these impurities and gives a timeline for doing so. FDA's nitrosamine information page⁸ lists metformin alongside ARBs, ranitidine and several other drugs.

ER metformin is still marketed. In late October 2026, FDA's shortage database¹⁰ added one ER metformin tablet listing as "to be discontinued," the category our piece on discontinued drugs on the shortage list explains, citing a business decision by the manufacturer; the entry says nothing about impurities. Readers who want to check a specific bottle can use GxRadar's guide to checking whether a medicine was recalled, and questions about a particular prescription are best taken to a pharmacist or prescriber.