The US Food and Drug Administration (FDA) has asked companies to stop selling all forms of the heartburn drug Zantac, after an investigation found that potential cancer-causing contaminants can build up in the product over time.

The FDA has asked manufacturers of the prescription and over-the-counter drug to pull all supplies from the market with immediate effect.

Consumers were also warned to stop taking the drug and to dispose of any remaining liquids or tablets following FDA disposal instructions.

The agency added that people should not return their Zantac drugs to “drug take-back” locations during the coronavirus pandemic.

In a statement on Wednesday, the FDA said the withdrawal of all ranitidine products, commonly known as Zantac, from the market was the latest step in an ongoing investigation of a contaminant known as N-Nitrosodimethylamine (NDMA).

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“We didn’t observe unacceptable levels of NDMA in many of the samples that we tested,” said Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research.

“However, since we don’t know how or for how long the product might have been stored, we decided that it should not be available to consumers and patients unless its quality can be assured.”

According to the FDA, levels of the contaminant increased over time and when stored at “higher-than-normal” temperatures.

In September, the FDA advised Zantac users to consider switching drugs after it found low levels of NDMA — a probable carcinogen to humans, that can increase the risk of cancer.

Some pharmacy chains such as Walgreens, Walmart and CVS Pharmacy — as well as manufacturers of Zantac — already suspended selling and making the drug several months ago.