The Food and Drug Administration on Wednesday asked companies to stop selling all forms of the heartburn drug Zantac, after concluding that a potential cancer-causing contaminant can build up in the drug when stored for long periods.
The agency also recommended that consumers who use over-the-counter forms of the drug, also known as ranitidine, stop taking it and that they should dispose of any tablets or liquid that they have. People who take prescription forms of the drug should speak with their doctors about other options before stopping treatment.
Most manufacturers withdrew their products from the market several months ago, after an outside pharmacy raised the alarm about the drug last year. Large pharmacy chains, including Walgreens, Rite Aid and CVS, had also removed all of the products from their shelves.
The F.D.A. said in September that the contaminant was a type of nitrosamine called N-nitrosodimethylamine, or NDMA, which is believed to be carcinogenic in humans and is found in a variety of products, including cured meats.
In a statement, Sanofi, the manufacturer of the brand-name version of Zantac, said that it recalled the product in October, and that all retailers and consumers were previously instructed to return or destroy the product.
“We take this issue seriously and continue to work closely with the F.D.A. to evaluate any potential safety risks associated with Zantac,” the company said. “At Sanofi, we stand by the longstanding science that supports the safety of Zantac OTC products, which have been used by consumers for over two decades.”
The F.D.A.’s investigation was prompted by the findings of an online pharmacy, Valisure, which had petitioned the agency to request a recall of all products containing ranitidine because it said its own tests had revealed high levels of NDMA, above the F.D.A.’s acceptable daily limit.
“We’re very happy about the fact that our laboratory testing has had such an impact, and we strongly support and applaud the F.D.A.’s decision,” said David Light, a founder and chief executive of Valisure.
The problem with ranitidine surfaced last spring, when Valisure, which tests the drugs it sells for quality, began analyzing its products for NDMA. Ranitidine was one of the first ones it tested, because the infant daughter of Mr. Light’s co-founder, Adam Clark-Joseph, had been prescribed the drug in syrup form. “We obviously saw dramatic results,” Mr. Light said, adding that some syrup versions of ranitidine were still on the market until Wednesday.
At the time of its testing, Valisure speculated that the source of the contaminant was the result of the “inherent instability” of the ranitidine molecule, which can degrade under certain conditions, such as high temperatures, to create NDMA.
But the F.D.A. initially pushed back against the pharmacy’s testing methods, saying the results were invalid because the pharmacy had heated the product, which created the higher levels of NDMA.
On Wednesday, however, the agency appeared to confirm Valisure’s findings, saying that “the impurity in some ranitidine products increases over time and when stored at higher than room temperatures and may result in consumer exposure to unacceptable levels of this impurity.”
Mr. Light said Valisure is researching what the long-term effects of taking the drug might be. “That remains very concerning to us,” he said.
The F.D.A. said people could consider other heartburn products that did not contain NDMA, according to its testing. They include brand and generic forms of Pepcid, Tagamet, Nexium, Prevacid and Prilosec.
