On Wednesday, the U.S. Food and Drug Administration requested that companies pull all prescription and over-the-counter forms of the heartburn drug Zantac (ranitidine) from store shelves. The agency has warned that an impurity in the drugs has been linked to an increased risk of cancer, which has become the subject of litigation against manufacturers of the drugs.

The impurity, N-Nitrosodimethylamine (NDMA), is commonly ingested in the human diet. NDMA is present in low levels in food and water. But the FDA discovered that the NDMA in Zantac increases over time, especially when the product is exposed to higher temperatures during distribution and consumer handling of the drug. These increases in NDMA can expose those that take the drug to high levels of NDMA, which may increase the risk of cancer.

The FDA has now advised all manufacturers of Zantac and other ranitidine drugs to pull their products from the market. Many large pharmacies, like Walgreens, Rite Aid, and CVS, have already removed the products from their shelves. Sanofi, the manufacturer of brand-name Zantac, said that it recalled all its products last October and that it continues to work the FDA to assess safety risks with the product.

The agency also says that consumers should stop taking the drug if they are taking an over-the-counter version and speak to their health care professional about alternatives if they are taking a prescription version of the drug. The FDA says that it has not found NDMA in Pepcid, Tagamet, Nexium, Prevacid, or Prilosec, drugs which the agency has approved for the same or similar uses as Zantac. Nexium and Prilosec have problems of their own, however, as studies have linked those drugs to chronic kidney disease.

The FDA continues to investigate the issues with Zantac and encourages health care professionals and patients to report problems with the drug.