(CNN) Drugmaker Sanofi is voluntarily recalling of the heartburn medication Zantac OTC.

The recall impacts drugs sold in the United States and Canada. Sanofi is working with the US Food and Drug Administration to determine the extent of the recall.

Tests of Zantac and other ranitidine medications found N-nitrosodimethylamine, or NDMA, an impurity that is considered a possible carcinogen by the US Environmental Protection Agency , the FDA and Health Canada said in September. NDMA can be unintentionally introduced into manufacturing through certain chemical reactions.

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