Opioid painkillers have pushed aside heroin and cocaine as the biggest killer drugs, according to the Centers for Disease Control and Prevention.

Because of that, U.S. Senate Finance Committee leaders Max Baucus (D., Mont.) and Charles Grassley (R., Iowa) began an investigation this week into whether pharmaceutical companies are inappropriately pushing sales by funding doctors and quasi-independent organizations set up to produce positive literature about prescription painkillers.

The companies receiving letters were Chadds Ford-based Endo Pharmaceuticals Holdings Inc., Johnson & Johnson — which has operations in the Philadelphia area — and Purdue Pharma L.P. of Stamford, Conn.

"When it comes to these highly addictive painkillers, improper relationships between pharmaceutical companies and the organizations that promote their drugs can put lives at risk," Baucus said in a statement. "These painkillers have an important role in health care when prescribed and used properly, but pushing misinformation on consumers to boost profits is not only wrong, it's dangerous."

In the letters, which are available on the Senate Finance Committee website, the senators asked companies to provide information on payments made from 1997 to the present to eight people, seven of whom are doctors.

One of the doctors is Rollin Gallagher, who is listed as director of pain management at the Philadelphia Veteran Affairs Medical Center. Gallagher could not be reached for comment Thursday night.

The senators want information from and about the American Pain Foundation, the American Academy of Pain Medicine, the American Pain Society, the Center for Practical Bioethics, the Wisconsin Pain and Policy Study Group, the Joint Commission on Accreditation of Healthcare Organizations, and the Federation of State Medical Boards.

"Something has to change," Grassley said in a statement. "A greater understanding of the extent to which drugmakers underwrite literature on opioids is a good start."

Endo said it is cooperating.

"Part of Endo's corporate mission is a commitment to educating physicians and patients about the responsible use of pain management therapies," an Endo spokesman said by e-mail.

"Endo continues to demonstrate good corporate citizenship by prioritizing appropriate therapy use and patient health and safety. We work closely with government agencies, such as the FDA and DEA, to ensure open lines of communication and aligned actions for the good of patients and society as a whole. And we look forward to cooperating with the Senate Finance Committee."

Contact David Sell at 215-854-4506, dsell@phillynews.com or on Twitter @PhillyPharma. Read his PhillyPharma blog on philly.com.