(CNN) Walmart, the United States' largest retailer, is the latest to announce it's suspending the sale of Zantac and other over-the-counter ranitidine medications due to concerns they might contain a substance that can cause cancer. Customers can return the products to Walmart or Sam's Club stores for a refund.

CVS Pharmacy and Walgreens also recently announced they are no longer selling the medications.

CVS, the largest pharmacy chain in the country, said over the weekend it was suspending sale of Zantac and other products which contain ranitidine until further notice. Zantac and its CVS-branded generic counterpart have not been recalled, a statement from CVS said, and the FDA has not recommended that patients stop taking ranitidine products. Customers who have already bought the products can return them to CVS for a refund, CVS said.

Walgreens said in a statement it is removing the medications from shelves while the US Food and Drug Administration continues its review of the products.

The FDA said last month that some ranitidine medications -- including those known by the brand name Zantac -- contain low levels of an impurity that could cause cancer.

Read More