The Food and Drug Administration announced it has found low levels of a cancer-causing chemical in heartburn medicine samples containing the drug that’s sold under the brand-name Zantac, The New York Times reports. The agency said it found low levels of a type of nitrosamine called NDMA in the drug, known as ranitidine. NDMA could cause tumors in the liver and other organs in lab animals, and is believed to be carcinogenic in humans. NDMA can form in the drug manufacturing process if chemical reactions used in production aren’t controlled or monitored carefully enough, according to the FDA. Agency spokesman Jeremy Kahn said the FDA was still investigating the contamination and has not identified where it originated or how widespread the issue is. The European Medicines Agency is also looking into the matter.