(CNN) — Dr. Reddy’s Laboratories Ltd. and its subsidiaries issued a voluntary nationwide recall of its ranitidine medicines used to treat heartburn, the US Food and Drug Administration said on Wednesday.

Tests found some of the products were contaminated with N-Nitrosodimethylamine, or NDMA.

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NDMA is an impurity that is considered a possible carcinogen by the US Environmental Protection Agency. NDMA can be unintentionally introduced into manufacturing through certain chemical reactions.

The FDA has been testing several drugs after it found the impurity in blood pressure and heart failure medicines known as ARBs.

So far, Dr. Reddy’s hasn’t received any reports of illnesses related to patients taking the drug.

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Walmart, CVS Pharmacy and Walgreens recently announced they would halt sales of ranitidine medications because of concerns they might contain the impurity. In September, drug maker Novartis said it was halting distribution of all ranitidine medicines made by Sandoz.

Patients who are using medicines made by Dr. Reddy’s should ask their doctors or pharmacists about treatment going forward.

The FDA has been trying to determine what is causing this problem and has been working with international regulators to determine how the impurities are getting into these drugs.

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