Novartis International’s Sandoz division, which manufactures ranitidine, a generic form of the heartburn drug Zantac, has halted its distribution over concerns that it may be contaminated with low levels of a probable carcinogen. Sandoz has also issued a recall of the drug in the U.S., Canada and parts of Europe.* The U.S. Food and Drug Administration released a statement last week saying some ranitidine medicines, including the brand-name drug Zantac, contain traces of N-nitrosodimethylamine (NDMA). The FDA said NDMA levels found in the medications in early tests are not much higher than those in some common foods—but it is still investigating the potential risk to patients.

Zantac and other ranitidine drugs are used to prevent and treat gastroesophageal reflux and stomach ulcers. The medications come in both prescription and over-the-counter forms.

NDMA is known to cause cancer in animals, and the Environmental Protection Agency has said it is a “probable” human carcinogen. At high levels, the chemical has resulted in liver toxicity in rats, and chronic low doses have also been linked to liver and esophageal tumors in the animals. The chemical is sometimes found at low amounts in drinking water and many foods, including smoked or cured ones (such as bacon), as well as beer, fish and cheese. Preliminary tests show the levels found in ranitidine drugs “barely exceed” those in common foods, the FDA statement said. But Sandoz stopped distributing the drug out of an abundance of caution, according to spokesperson Michelle Bauman.

“Our first priority is patient safety,” Bauman says. Although the company would not comment on specific levels of NDMA in its products, she says that “any levels above the level set by the country are important to us.” She adds that Sandoz is working closely with the FDA to identify the cause of the contamination.

In its statement, the FDA said it is not currently calling for people to stop taking ranitidine but that individuals who are taking it in a prescription drug and want to stop should consult a doctor. When asked for comment, the agency said it “does not have any additional information to share at this time.”

French pharmaceutical company Sanofi, which manufactures Zantac, says, “There are currently no plans to stop distributing or manufacturing Zantac or other ranitidine products outside of Canada. We are working closely with the FDA and are conducting our own robust investigations to ensure we continue to meet the highest-quality safety and quality standards.”

NDMA has also been linked to blood-pressure and heart-failure medications called angiotensin II receptor blockers, leading to numerous recalls over the past year.

*Editor’s Note (9/24/19): This sentence was updated after posting to include news that Sandoz has extended its ranitidine recall to the U.S.