More than 30 advocacy groups want two senators to divulge the findings of a years-long investigation into opioid abuse.

The 36 groups wrote to the Senate Finance Committee on Wednesday requesting that it disclose its findings from a 2012 investigation into drug makers paying nonprofit medical groups to aggressively promote painkillers.

The committee sent letters to three opioid makers and seven nonprofit groups, and committee staff spent months investigating a slew of records. But none of that information has ever been made public, according to the letter to the committee.

"The results of the investigation are not simply a matter of historical importance," the letter said. "Some of these same companies and nonprofit groups have continued to promote aggressive opioid use and continue to block federal and state interventions that could reduce overprescribing."

The investigation looked into ties between manufacturers Johnson & Johnson, Purdue Pharma and Endo Pharmaceuticals with medical groups and doctors who have advocated the use of painkillers.

The senators asked the three manufacturers and seven medical groups to send information about their financial ties.

Since 2012, the opioid epidemic has raged. Every day nearly 7,000 people are treated in emergency rooms for abusing painkillers, according to the Centers for Disease Control and Prevention.

The committee's investigation was started by then-Sen. Max Baucus, D-Mont. When Republicans took over the Senate in 2014, Sen. Orrin Hatch, R-Utah, took over the committee.

Baucus is now an ambassador to China and no longer serves on the committee.

"While this was an investigation closed under a previous chairman during another Congress, Chairman Hatch believes this is an issue of serious concern and will be talking with members of the Finance Committee on how they would like to move forward," said committee spokeswoman Julia Lawless.

The opioid epidemic has even made its way onto the campaign trail. Democratic candidate Hillary Clinton released a plan earlier this month that provides $10 billion in new funding to combat the problem.

Various advocacy groups signed the letter, including Physicians for Responsible Opioid Prescribing, Public Citizen, National Coalition Against Prescription Drug Abuse and Change Addiction Now.