The Therapeutic Goods Administration (TGA) has investigated metformin-containing medicines for potential contamination with N-nitrosodimethylamine (NDMA). NDMA is classified as a probable human carcinogen and can be found in low levels in a variety of foods, some drinking water, and air pollution. It has also recently been detected in some ranitidine and angiotensin II antagonist medicines.

Testing of a selection of immediate-release and modified-release metformin products found that around 30% of batches contained NDMA at levels that modestly exceeded the acceptable limit. While one batch was found to have higher levels, limited stock of this product was supplied to the Australian market.

A risk analysis was conducted that included consideration of commonly prescribed doses. The TGA concludes that the risk is very low for patients taking metformin from batches that modestly exceed the NDMA limit. The limits set for NDMA are conservative and calculated so that an individual’s excess cancer risk would not exceed 1:100,000 if they received the maximum daily dose of that medicine for 70 years.

Metformin is an important treatment for type 2 diabetes. The TGA advises that the risks of untreated diabetes greatly outweigh the risks posed by the low levels of NDMA detected in these products. Patients are strongly recommended to continue taking their medication as prescribed.  The TGA is currently working with manufacturers and sponsors to improve processes and ensure that metformin products supplied in Australia meet the TGA’s high standards for quality.


  1. American Cancer Society. Known and Probable Human Carcinogens. Atlanta: American Cancer Society; 2019.
  2. Department of Health. Metformin: Low levels of contamination with N-nitrosodimethylamine (NDMA). Woden: Therapeutic Goods Administration; 2020.

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