In collaboration with the Food and Drug Administration (FDA), Xanodyne Pharmaceuticals, manufacturer of Darvon (propoxyphene) and Darvocet (propoxyphene + acetaminophen), has agreed to take the drugs off of the market after new clinical research shows that the drug puts patients at risk of potentially serious or even fatal heart rhythm abnormalities. Companies manufacturing generic versions of the drug have also agreed to remove all products from stores. "These new heart data significantly alter propoxyphene's risk-benefit profile," the FDA's John Jenkins said in a statement. "The drug's effectiveness in reducing pain is no longer enough to outweigh the drug's serious potential heart risks."

Propoxyphene, an opiod, is a narcotic pain-killer and cough suppressant which was approved in August of 1957, and works by causing sedation and respiratory depression. Side effects include dizziness, stomach pain, vomiting, and constipation. More serious side effects include skin rash and difficulty breathing.

Since 1978, the FDA has received two requests to remove the drug from the market, but decided against it, stating that the benefits far outweigh the risks. According to the Washington Post, in January of 2009, an FDA advisory committee recommended pulling the drug from the market, but decided against it in July of 2009, requiring that Xanodyne Pharmaceuticals conduct a new study assessing its safety. The complete removal of the drug is in response to the results of the study which showed that "even when taken at recommended doses, propoxyphene caused significant changes to the elecrical activty of the heart" that can cause serious problems, including sudden death, the FDA said.

Approximately 120 million prescriptions have been filled for propoxyphene in the United States.