CVS, Rite Aid, Walgreens and Walmart have voluntarily stopped sales of Zantac and their respective house brands because of an active ingredient that could cause cancer.

The FDA issued a warning in September after lab tests determined that ranitidine, a medication used in the over-the-counter stomach medications, contained low levels of N-nitrosodimethylamine, an environmental contaminant found in water, meats, dairy products and vegetables. It is considered a probable human carcinogen by the FDA.

CVS said customers can return their product for a refund.

Other heartburn medications will continue to be sold, including Pepcid, Nexium, Prilosec, Prevacid and Protonix.

The FDA said it is continuing to test ranitidine products from multiple manufacturers and assess the possible effect on patients who have been taking ranitidine.

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