This two-part investigation by The Center for Public Integrity and The Associated Press examines the politics behind the nation’s opioid addiction epidemic.

AP reporters Geoff Mulvihill and Matthew Perrone and Center for Public Integrity reporters Liz Essley Whyte and Ben Wieder collaborated on the project for seven months.

Wieder collected and analyzed campaign finance and lobbying data covering 2006 through 2015 from the National Institute on Money in State Politics, Center for Responsive Politics, Federal Election Commission, the U.S. House of Representatives Office of the Clerk and the IRS.

Mulvihill, Perrone and Whyte reviewed hundreds of documents and interviewed more than 150 officials, experts, advocates and others to gain insights into how the political process influenced the response to the opioid epidemic.

Taken together, this information provides a unique national look at how drugmakers and their allies often sought to delay steps intended to combat opioid abuse while pushing their own priorities with lawmakers and regulators. The findings were provided in advance to news outlets around the country to help reporters prepare stories for their local audiences and augment their ongoing reporting about the nation’s opioid crisis.

Part of a joint investigation by The Associated Press and The Center for Public Integrity