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All Zantac products and generic versions of the heartburn medication should be taken off pharmacy shelves immediately, the Food and Drug Administration announced Wednesday.

This includes prescription and over-the-counter forms of the antacid. The move comes after months of investigation into certain lots of ranitidine that were found to contain trace amounts of a contaminant called N-Nitrosodimethylamine (NDMA).

⚠️FDA requests market withdrawal of all remaining prescription and OTC ranitidine (Zantac) products on the U.S. market. This means that ranitidine will not be available for use in the U.S. https://t.co/kfcW0wlHo6 pic.twitter.com/IvrLcmrMn5 — FDA Drug Information (@FDA_Drug_Info) April 1, 2020

The World Health Organization has classified the contaminant as a "probable human carcinogen."

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The FDA "has determined that the impurity in some ranitidine products increases over time and when stored at higher than room temperatures," the agency wrote in a news release.

That "may result in consumer exposure to unacceptable levels of this impurity," the FDA wrote, but added that the agency had not actually detected a level that would be considered "unacceptable" in many tested samples.

"However, since we don't know how or for how long the product might have been stored, we decided that it should not be available to consumers and patients unless its quality can be assured," Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, wrote in the news release.

The FDA's advisory said people already taking Zantac, made by Sanofi, or generic forms of the antacid should stop and switch to other heartburn medications that do not contain ranitidine.

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