NDMA and Nitrosamine Contamination: The Drug Recall Problem That Won't Go Away

N-nitrosodimethylamine, or NDMA, is a nitrosamine — a class of chemical compounds formed when secondary amines react with nitrous acid or other nitrosating agents under certain conditions. NDMA is classified by the International Agency for Research on Cancer (IARC) as a Group 2A carcinogen — meaning it is a probable human carcinogen based on evidence from animal studies and limited human epidemiological data.

NDMA is not unique to pharmaceuticals. It occurs naturally in some foods — particularly cured and smoked meats, beer, and some cheeses — and can form in water treated with chloramines. The FDA has established that very low levels of NDMA (below 96 nanograms per day) are acceptable in drug products, based on a theoretical calculation of acceptable daily intake that reflects a one-in-100,000 lifetime cancer risk increase.

The problem discovered in 2018 was that some medications contained NDMA at levels far above this acceptable daily intake threshold — in some cases hundreds of times higher — due to contamination introduced during manufacturing.

The contamination pathways differ across affected drugs and are technically complex, but they share a common theme: manufacturing conditions that allowed nitrosamine formation as a byproduct of chemical synthesis or degradation.

For valsartan and related blood pressure drugs (the sartan class), the contamination originated primarily at a Chinese manufacturer, Zhejiang Huahai, that had changed its manufacturing process in 2012. The new process created conditions that allowed NDMA to form during synthesis of the active pharmaceutical ingredient. Because the manufacturing change predated the realization that NDMA could form this way, and because routine finished-product testing did not specifically screen for NDMA, the contamination went undetected for years.

Ranitidine (Zantac) was different: the contamination was inherent to the ranitidine molecule itself, which is chemically unstable and can degrade to form NDMA over time, particularly at elevated temperatures. This meant the problem was not specific to any manufacturer — all ranitidine products had this potential, and in 2020 the FDA withdrew approval for all ranitidine medications from the U.S. market entirely.

Metformin contamination, discovered in 2020, involved NDMA formation during the manufacturing process in some production batches. Unlike ranitidine, metformin itself is not inherently unstable, but certain manufacturing conditions can generate NDMA as a process impurity.

If a medication you take has been recalled for nitrosamine contamination, the most important step is to check whether your specific lot number is among the recalled lots. Not every batch of a medication is affected — recalls typically target specific production runs. Your pharmacy can identify the lot number of your dispensed medication and confirm whether it is included in a recall.

For medications where your lot is recalled, do not abruptly stop a prescription medication without consulting your doctor or pharmacist, even if the contamination sounds alarming. For chronic conditions like hypertension and diabetes, the risks of untreated disease typically outweigh the theoretical cancer risk from a limited period of exposure to elevated NDMA — particularly because cancer risk from NDMA is cumulative and long-term, while the health consequences of stopping blood pressure or diabetes medication can be immediate.

The FDA's public risk communications for NDMA recalls have consistently communicated that the increased cancer risk from short-term exposure — even at elevated levels — is low in absolute terms. The agency's statements typically note that exposure to the drug before the recall is identified is unlikely to cause harm but that continued long-term exposure above the acceptable daily intake threshold should be avoided. This framing is the right one to use when thinking about your own exposure.

Despite years of regulatory attention since 2018, nitrosamine contamination in drugs remains an ongoing issue. The FDA has required pharmaceutical manufacturers to evaluate all drug products for potential nitrosamine impurities, and new manufacturing guidelines have been issued. But the analytical chemistry of detecting nitrosamines at trace levels in complex drug matrices is challenging, and the number of possible nitrosamine impurities (there are many besides NDMA) creates a large testing burden.

New nitrosamine-related recalls continue to emerge as manufacturers identify previously uncharacterized impurities in their products. The FDA maintains a running list of drug product recalls related to nitrosamine contamination at its website, which is updated as new recalls are announced. If you take multiple prescription medications chronically, periodically checking whether any have been the subject of nitrosamine recalls is a reasonable precaution.