The Food and Drug Administration announced Friday that low levels of a cancer-linked chemical have been found in samples of the heartburn medication Zantac.
The chemical is an impurity called NDMA, which has been linked to an increased risk for colorectal and uterine cancers.
The FDA said that low levels of NDMA were found in samples of ranitidine, a drug used to treat and prevent heartburn by reducing stomach acid. It's sold under the brand name Zantac.
It's unclear where the contamination originated. NDMA is the same chemical that lead to multiple recalls of blood pressure medicines this past year.
Currently, there is no recall of Zantac or any medicines that contain ranitidine.
The FDA said it's still evaluating whether the levels found in antacids would pose a health risk to the millions of people who take them, and has said people should not stop taking their heartburn medicine until more is known.
Health officials in Europe announced Friday they, too, are investigating NDMA contamination in ranitidine.
Other heartburn drugs on the market, such as Prevacid, Nexium and Prilosec, have different ingredients and are not included in this alert.
"Patients should be able to trust that their medicines are as safe as they can be and that the benefits of taking them outweigh any risk to their health," Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, said in a statement.
"Although NDMA may cause harm in large amounts, the levels the FDA is finding in ranitidine from preliminary tests barely exceed amounts you might expect to find in common foods," the statement continued.
According to the Centers for Disease Control and Prevention, NDMA has been detected in tobacco smoke, chewing tobacco and cured meats such as bacon.
Ranitidine is sold over the counter as a heartburn medicine, but is also used as a prescription to treat stomach ulcers and gastroesophageal reflux disease.
More than 15 million prescriptions were written for ranitidine in 2016.