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The Food and Drug Administration has recalled several more lots of heartburn medications, including more generic versions of Zantac, that have been found to contain trace amounts of a substance that may be linked to cancer.

The World Health Organization has classified that substance, N-Nitrosodimethylamine (NDMA), as a "probable human carcinogen."

The FDA said that Denton Pharma Inc. had recalled several batches of unexpired ranitidine tablets due to the possible presence of NDMA. Ranitidine is the generic version of the popular heartburn drug Zantac.

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The recalled batches include certain lots of ranitidine tablets in 150 milligram and 300 mg strengths.

Appco Pharma has also recalled batches of ranitidine because of the potential presence of NDMA. The recalled lots have an expiration date of April or May 2021.

None of the recalled lots has been associated with any injuries or adverse events.

On Wednesday, the FDA also announced that the drug company Mylan has recalled three lots of another antacid, nizatidine, which were also found to contain trace amounts of NDMA. Those capsules, in 150mg and 300mg strengths, were manufactured by Solara Active Pharma Sciences Limited.

Mylan Initiates Voluntary Nationwide Recall of 3 Lots of Nizatidine Capsules, USP, Due to Trace Amounts of NDMA (N-Nitrosodimethylamine) Impurity Found in the Active Pharmaceutical Ingredient Manufactured by Solara Active Pharma Sciences Limited https://t.co/pSd3xmViUT pic.twitter.com/1z5hO7rL3f — U.S. FDA (@FDArecalls) January 9, 2020

Nizatidine is used for short-term treatment of stomach ulcers as well as heartburn caused by gastroesophageal reflux disease, the FDA wrote on its website.

Recalled batches include nizatidine capsules sold in bottles of 60 with an expiration date of May, as well as nizatidine capsules sold in bottles of 30 with an expiration date of January.

The FDA said it has not received any reports of injuries associated with taking the medications. It's unclear whether such trace amounts of the carcinogens would cause harm when taken as directed. FDA testing of recalled ranitidine detected NDMA levels similar to the levels found in grilled and smoked meats.

Federal regulators said other heartburn medications, such as famotidine (Pepcid), cimetidine (Tagamet), esomeprazole (Nexium), lansoprazole (Prevacid) and omeprazole (Prilosec) have not tested positive for signs of NDMA.

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