The pharmacy chains Walgreens and CVS have stopped selling the heartburn medicine Zantac and its generic versions after the Food and Drug Administration warned this month that it had detected low levels of a cancer-causing chemical in samples of the drug.
A Walgreens spokesman said in a statement on Monday that the company had pulled the drug from its shelves “while the FDA continues its review of the products.”
Walgreens and CVS, which announced its move on Saturday, both noted that the drug, which is known as ranitidine, has not been recalled. The companies said customers who had bought the products could return them for a refund.
The F.D.A. has said it is investigating the source of the contamination as well as the risk to patients, recommending that they talk to their doctors and that those who take over-the-counter versions consider switching to a different medication.
Zantac, the brand-name version of the drug, is sold by Sanofi, but generic versions are widely sold.
This month, the drug maker Novartis said that its generic-drug division, Sandoz, had stopped distributing a prescription form of ranitidine worldwide while it investigates the F.D.A.’s findings. GlaxoSmithKline has also stopped shipping its generic version of the drug, as well as Dr. Reddy’s Laboratories, a major generic manufacturer.
The companies, including Sanofi, have stopped short of recalling their products in the United States. In a statement on Monday, Sanofi said that the levels of the contaminant that the F.D.A. had found in “preliminary tests barely exceed amounts found in common foods.”
The company added: “We are working closely with the F.D.A. and are conducting our own robust investigations to ensure we continue to meet the highest quality safety and quality standards.”
Last week, Apotex, which makes store-branded versions of Zantac for Walgreens, Walmart and Rite-Aid, recalled its ranitidine products.
The European Medicines Agency is also reviewing the drug. Canada has ordered a halt to all distribution of ranitidine while it investigates.
In its warning on Sept. 13, the F.D.A. said that it had found low levels of a cancer-causing contaminant, a type of nitrosamine called nitrosodimethylamine, or NDMA, in the heartburn medications.
Nitrosamines can cause tumors in the liver and other organs in lab animals, and they are believed to be carcinogenic in humans. NDMA can form during manufacturing if the chemical reactions used to make the drug are not carefully controlled, the F.D.A. has said.
Ranitidine is a histamine blocker that works to lower the acid created in the stomach, according to the F.D.A. The medication is sometimes prescribed to prevent ulcers of the stomach and intestines as well as gastroesophageal reflux disease, the agency says.
CVS said it would continue to sell other histamine blockers, including Pepcid, Tagamet and the generic equivalents famotidine and cimetidine.
Katie Thomas contributed reporting.