A U.S. Senate panel has launched a probe of possible links between three drugmakers and nonprofit medical groups that advocated for increasing the use of prescription painkillers, now the target of a nationwide law enforcement crackdown.

Senate Finance Committee Chairman Max Baucus, a Democrat, and the panel's leading Republican, Senator Chuck Grassley, said the drugmakers and allied groups could be behind dubious marketing practices that have coincided with a huge jump in deadly overdoses from painkillers known as opioids.

"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," Baucus said in a statement.

Baucus and Grassley said they sent letters to drugmakers Johnson & Johnson 's Janssen Pharmaceuticals unit, Endo Pharmaceuticals and Purdue Pharma and seven medical groups seeking documents about their financial connections.

Purdue Pharma and Janssen both issued statements saying they were reviewing the letters and would work with the committee. There was no immediate response from Endo Pharmaceuticals.

Lawmakers hope to find out if medical groups have promoted misleading information about the risks and benefits of opioid use while receiving financial support from manufacturers.

The Senate investigation comes at a time when federal, state and local law enforcement officials are coming to grips with a national epidemic involving the illicit use of prescription drugs. Their abuse has surpassed heroin and cocaine as a source of fatal overdoses.

Opioids were involved in 14,800 overdose deaths in 2008, more than cocaine and heroin combined, according to the U.S. Centers for Disease Control and Prevention.

A crackdown spearheaded by the U.S. Drug Enforcement Administration has included healthcare companies including two Florida pharmacies operated by CVS Caremark and a distribution facility owned by Cardinal Health.

Privately owned Purdue Pharma is the maker of OxyContin. Endo manufactures Percocet. Both have been linked to addiction and overdoses.

"There is growing evidence pharmaceutical companies that manufacture and market opioids may be responsible, at least in part, for this evidence by promoting misleading information," Baucus and Grassley said in their letters.

One of the groups, the American Pain Foundation, posted a notice on its Web site saying its board of directors voted May 3 to dissolve the organization because of ongoing financial obligations.

The Senate probe follows an investigation by nonprofit news website ProPublica and The Washington Post, which found that the American Pain Foundation received 90% of its funding from the drug and medical device industry in 2010.

At the same time, it produced its guides for patients, policymakers and journalists that played down the risks of opioid painkillers and promoted the benefits.