A bipartisan group of state attorneys general, including Iowa Attorney General Tom Miller, is expanding a multistate investigation of manufacturers and distributors of prescription opioid drugs as part of a widespread probe into the nation’s opioid epidemic. The 40 states and the District of Columbia served investigative subpoenas for documents and information on Endo, Janssen, Teva/Cephalon and Allergan, and served a supplemental civil investigative demand on Purdue Pharma, which they began investigating in June. The states are also seeking documents and information about distribution practices from three pharmaceutical distribution companies -- AmerisourceBergen, Cardinal Health and McKesson -- that together manage approximately 85 percent of the nation's opioid distribution. The investigation will help the states determine whether manufacturers and distributors engaged in unlawful practices in the marketing, sale and distribution of opioids. According to the Centers for Disease Control and Prevention’s latest report, opioids were involved in 33,091 deaths across the U.S. in 2015, and opioid overdoses have quadrupled since 1999.