Merck & Co. halted the sale of Vioxx worldwide because data from a three-year study conducted by the drug company discovered that participants in the research had double the risk of a heart attack. Dr. James Leisen, director of rheumatology at Wayne State University, said his staff has not seen any heart problems associated with Vioxx. \"I don\'t think people should be alarmed,\" he said. \"There are safety concerns, but that is primarily with higher doses - 50 milligram doses. Those taking it won\'t be in trouble if they take the 25 milligram dose,\" Leisen said.