The U.S. Food and Drug Administration is investigating whether the diabetes drug metformin had unsafe levels of a cancer-causing chemical and will recommend recalls as appropriate, the agency said on Thursday. The move is part of the agency's broader push to investigate a range of drugs for the presence of the carcinogen, known as N-nitrosodimethylamine (NDMA), with popular heartburn medication Zantac being recalled this year for fear it contained NDMA. The FDA later downplayed those fears, saying levels of contamination in the drug, also known as ranitidine, "are similar to the levels you would expect to be exposed to if you ate common foods like grilled or smoked meats."Metformin is a first-line medication for the treatment of type 2 diabetes. It helps control high blood sugar and is marketed under a number of brand names, including Fortamet and Glucophage. The FDA's investigation follows other countries' findings of low levels of NDMA in in metformin drugs there, the agency said. Based on its information, the FDA added, NDMA in those drugs ranged within naturally occurring levels in food and water. "The FDA is investigating whether metformin in the U.S. market contains NDMA, and whether it is above the acceptable daily intake limit of 96 nanograms," said Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research. The agency will "recommend recalls as appropriate if high levels of NDMA are found," she added in the statement. Such action could put treatment out of reach for some sufferers, one expert said. "If these reports are true, it could be a big blow to many millions of people on this drug," said Ranit Mishori, a professor of family medicine at Georgetown University. "There are many other alternatives and other medication classes but many of them have side effects, are more expensive and some of the newest ones may not be covered by insurance."