The latest lawsuit, filed by Alabama last week, claimed the pharma company deceptively marketed prescription opioids.
Reports about OxyContin abuse began to surface by early 2000, according to a 2003 government report. Medical professionals say a shift in the 1990s to "institutionalize" pain management opened the doors for pharmaceutical companies to encourage the mass prescribing of painkillers by doctors, and Purdue Pharma led that effort.
Purdue Pharma, the maker of OxyContin, contributed the most to the groups, funneling $4.7 million to organizations and physicians from 2012 through a year ago.
"Doctors and the public have no way of knowing the true source of this information and that's why we have to take steps to provide transparency", said McCaskill in an interview with The Associated Press. Another drugmaker, Insys, said it was not able to comment immediately, while Teva Pharmaceutical Industries did not immediately respond to a request for comment.
Purdue has slung OxyContin on doctors since it was approved in '95, and has pulled out all the stops to promote it in marketing campaigns.
Sen. Claire McCaskill released a report Monday alleging that from 2012 to 2017, leading manufacturers of opioids gave $9 million to pain treatment advocacy groups, an arrangement the report says "may have played a significant role in creating the necessary conditions for the US opioids epidemic". Data from the CDC in 2016 says that opioids were the cause of 42,000 overdose deaths during that year, reports Business Insider.
Last year, it was one of several drugmakers accused of marketing opioid painkillers as a safe product - only to fuel a nationwide drug epidemic.
The Sackler family owns Purdue Pharma, and has accumulated a fortune estimated at about $14 billion dollars by Forbes in 2015, by distributing the highly addictive- and deadly- opioid painkiller OxyContin as a purportedly non-addictive version of oxycodone. Purdue said in a statement that it supported organisations interested in helping patients receive appropriate care.
A company spokesman declined to comment. While the groups aren't required to disclose their donors publicly, McCaskill said that should be changed. Janssen told the AP the company acted responsibly; Mylan objected to being included because of its "minuscule role" in opioid sales and marketing; while calls and emails to Depomed were not returned.