Concern over reports that link diabetes drugs to heart trouble is compelling U.S. drug regulators to ask diabetes-drug makers for more safety data. These requests for additional data could delay new product approvals by years and add millions of dollars to development and post-market commitment costs.The U.S. Food and Drug Administration is reportedly sending letters to all companies with diabetes drugs in development, informing them that the agency will now require safety data prior to approval that measures a drug's cardiovascular risk. Companies reportedly receiving the FDA letters include Amylin Pharmaceuticals ( AMLN), Vivus ( VVUS), Incyte Pharmaceuticals ( INCY) and Roche, according to sources familiar with the letters. All have diabetes drugs in mid- to late-stage clinical trials. "It appears companies with drugs at the FDA -- Novo Nordisk ( NVO)(liraglutide), Takeda (alogliptin) and AstraZeneca ( AZN)/ Bristol-Myers Squibb ( BMY) (saxagliptin) -- have not yet received a letter, although discussions with industry participants lead us to believe they are coming," wrote Morgan Stanley biotech analyst Steve Harr in a note to clients on Friday. "The companies under review have the greatest uncertainty, and outcomes will impact these companies and competitors." Novo Nordisk's drug, liraglutide, is expected to be discussed at an upcoming advisory panel meeting. An FDA spokesperson would not comment on the letters, stating only that the agency is working on guidance on issues surrounding cardiovascular risk and diabetes drugs. Research published in 2007 linked Avandia, a diabetes drug marketed by GlaxoSmithKline ( GSK), to an increased risk of heart attack in people with type 2 diabetes. Since then, the cardiovascular risk of all diabetes drugs has become a major concern for regulators both in Europe and the U.S.