The Senate Finance Committee is looking to crack down on unnecessary pain prescriptions through a follow-the-money investigation probing the conflicts of interest between advocacy groups and drug marketers.

A total of 10 letters were sent to a mix of pharmaceutical companies and pain medication advocacy groups Tuesday, asking for an accounting of payments given and/or received from the pharmaceutical industry. The letters, signed by committee chair Sen. Max Baucus (D-MT) and Sen. Chuck Grassley (R-IA), went out Tuesday. The senators say they were spurred by the spiraling number of prescriptions for opiates, like Purdue Pharma’s Oxycontin, and marketing practices the senators say have been documented as misleading.

“Doctors and patients should know if the medical literature and groups that guide the drugs’ use are paid for by the drugs’ manufacturers and if so, how much,” Grassley said in a statement.

Of particular interest is the publication Responsible Opioid Prescribing: a Clinician’s Guide, published by the Federation of State Medical Boards, a trade group. The FSMB’s website says the publication “provides prescribers with an understanding of expectations of regulators and offers pragmatic steps for adopting a risk-management approach associated with any use of opioid drugs.”

The senators’ letters indicate otherwise, citing among the reasons for its inquiry Milwaukee Journal Sentinel/MedPage Today reports that the FSMB’s handbook has been criticized for lacking a scientific basis for its recommendations to prescribe opioids for non-cancer-related pain. They also cite work by non-profit news organization ProPublica highlighting financial connections between pain advocacy groups and opioid manufacturers that it says resulted in misleading physician and patient materials.

The Federation of State Medical Boards did not return calls by press time.

The CDC says opioid pain medications now kill more people than heroin and cocaine combined, and accounted for almost 74% of fatal prescription drug overdoses in 2008. A 2011 GAO report links prescription pain killers to a 142% spike in emergency room visits between 2004 and 2009. The senators also cite CDC statistics of rising opioid abuse as a reason for their inquiry. Pain doctors and advocacy groups say statistics show most of the deaths have been linked to illicitly obtained drugs rather than to patients who get them from their doctors.

Tuesday’s letters follow those that date to 2010, in which Sen. Grassley asked Medicaid programs to explain rising prescription rates for anti-psychotics, anti-anxiety drugs and pain-killers. Oxycontin was among the most highly prescribed medications in 33 states and the District of Columbia.

The new follow-the-money letters seek to identify the financial ties and possibly implied incentives that flow between the donors and recipients, demanding that Endo Pharmaceuticals, Purdue Pharma and Johnson & Johnson provide a clear accounting of funds provided to organizations including the American Pain Foundation, The American Academy of Pain Medicine, The American Geriatric Society, The Wisconsin Pain and Policy Study Group and the Federation of State Medical Boards, among others. The senators are also asking pharmaceutical companies to provide all communications that pertain to pain-management guidelines or policies.

“We have received the letter from Chairman Baucus and Sen. Grassley and are in the process of reviewing it. We look forward to cooperating with the committee on this matter,” Purdue told MM&M. A spokesman could not confirm whether the letters took anyone in the company by surprise.

Janssen, a Johnson & Johnson subsidiary, released a similar statement, highlighting that it has disclosed financial payments made to healthcare professionals since 2010. Endo did not respond by press time.

The committee askedthe non-profit American Pain Foundation to name the company that provided $200,000 in seed money for the foundation’s 1997 launch as well as any financial support or collaborations with any company or organization that develops, manufactures, produces, markets or promotes opioid drugs. As of Wednesday, APF had shut down its main webpage. It has kept its sister site PainAid live, but the contact information has been disabled.

Although the inquiry strikes at the much-contested intersection between financial support and corporate interests, Sean Morrison, a professor of palliative medicine geriatrics and a director of the National Palliative Care Research Center, said the inquiry needs to be modified, because it puts cancer patients in the same bucket as those who are abusing opiate medications.

“It points to the real issues…of the lack of a clear firewall between philanthropic support [and] medical research and [between] medical advocacy and marketing” he told MM&M.

Morrison said that the lack of separation colors the potentially good work that an advocacy organization does. He said the Wisconsin Pain and Policy Study Group, which is a subject of the Senate inquiry, has helped patients worldwide, yet, like other organizations, has received financial support from the pharmaceutical industry. He said that with such an overlap “clearly there could be a perception of conflict of interest.”