In 2011 the U.S. Food and Drug Administration (FDA) found that the livers of roxarsone-treated chickens had elevated levels of iAs,2 a known human carcinogen.3 In response, roxarsone’s manufacturer, Pfizer, voluntarily pulled the drug off the U.S. market, although it is still sold overseas, and a similar arsenical drug is still available in the United States.4 Sampling for the new study
took place between December 2010 and June 2011, before Pfizer withdrew roxarsone from the U.S. market.