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Doctors who prescribe painkillers should be required to undergo training aimed at reducing misuse and abuse of the medications, according to federal health advisers, though they acknowledge the challenge of putting such a mandate in place.

The group of advisers to the Food and Drug Administration voted unanimously Wednesday that the agency should change its risk-management programs for opioid painkillers, highly addictive medications at the center of a national epidemic of addiction and abuse.

OxyContin was reformulated in 2010 to make it harder for addicts to crush the pills for a quick high. AP

Panelists said the risk plans should apply to all prescription painkillers, including immediate-release drugs like Vicodin and Percocet. Currently, the measures only apply to long-acting drugs like OxyContin, which slowly release their ingredients over 12 hours or more.

"If we keep it voluntary we're never going to get many people trained."

It's the second time since 2010 that an FDA panel has recommended expanding painkiller-safety measures and mandating training for doctors. But the training plans instituted about four years ago are voluntary, and FDA figures show that fewer than half of the doctors targeted by the effort have completed the training.

Related: FDA Strengthens Safety Warnings on Painkiller

Panelists said a more vigorous response is needed.

"If we keep it voluntary we're never going to get many people trained," said Michael Fry, a pharmacist with Providence Health system in Oregon.

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But how to require some 1.5 million prescribers across the U.S. to take hours-long classes about responsible opioid prescribing remains unclear.

The FDA says it supports linking training requirements to prescribers' federal licensure with the Drug Enforcement Administration, but putting that requirement in place would take a legal change by Congress. The FDA has its own authority to require training but it generally only uses it for specialized medications taken by small groups of patients. Opioids are among the most widely prescribed drugs in the nation, with more than 170 million prescriptions filled last year.

"Bureaucracy has to be challenged," said Dr. Martin Garcia-Bunuel. "We have a responsibility to do the right thing."

Related: CDC's New Opioid Advice is to Use Less

Prescription opioid overdoses have been rising steadily for well over a decade, reaching nearly 19,000 in 2014 - the highest number on record. Total opioid overdoses exceeded 28,600 that year when combined with heroin, which many abusers switch to after becoming hooked on painkillers.

Despite a full day of presentations on various metrics and data, most panelists said it's unclear whether the risk plans have actually helped curb misuse and abuse of the drugs. Along with the training programs, patients receive safety brochures about the risks of addiction and overdose at the pharmacy.

While overall painkiller prescriptions have fallen slightly over the last five years, that trend began before the safety programs took effect. At the same time, overdose deaths tracked by federal scientists have continued to rise.

Among other problems, panelists said it's unclear which deaths are being caused by inappropriately prescribed drugs, versus those sold on the black market.

Multiple panelists described the data used to assess the programs as "poor," including self-reported surveys by doctors.

Related: Obama Pushes for Better Addiction Treatment

"The data does not give us a clear indication of whether we are reaching the target population for the crisis we are trying to resolve," said Joseph O'Brien, the panel's patient representative.

The FDA is not required to follow the advice of its panelists, though it often does.

The educational programs are funded by 23 companies that market the long-acting opioids, including OxyContin-maker Purdue Pharma, Endo Pharmaceuticals, Pfizer Inc. and Johnson & Johnson. The content of the training is based on FDA instructions and administered by medical education companies.

In the last year, government authorities have launched a number of steps intended to reduce painkiller deaths, including new federal prescribing guidelines from the Centers for Disease Control and Prevention and state measures that restrict and track opioid prescribing.