This story was co-published with USA Today and NPR’s Shots blog.

Despite a national crackdown on prescription drug abuse, doctors churned out an ever-larger number of prescriptions for the most-potent controlled substances to Medicare patients, new data shows.

In addition, ProPublica found, the most prolific prescribers of such drugs as oxycodone, fentanyl, morphine and Ritalin often have worrisome records.

In 2012, the most recent year for which data is available, Medicare covered nearly 27 million prescriptions for powerful narcotic painkillers and stimulants with the highest potential for abuse and dependence. That’s up 9 percent over 2011, compared to a 5 percent increase in Medicare prescriptions overall. Even taking into account an increase in the number of Medicare enrollees, the prescribing rate rose slightly for these drugs, which are classified as Schedule 2 controlled substances by the Drug Enforcement Administration.

Twelve of Medicare’s top 20 prescribers of Schedule 2 drugs in 2012 have faced disciplinary actions by their state medical boards or criminal charges related to their medical practices, and another had documents seized from his office by federal agents.

The No. 1 prescriber—Dr. Shelinder Aggarwal of Huntsville, Ala., with more than 14,000 Schedule 2 prescriptions in 2012—had his controlled substances certificate suspended by the state medical board in March 2013. He surrendered his medical license four months later. (Aggarwal could not be reached for comment.)

Prescribing high volumes of Schedule 2 drugs can indicate a doctor is running a pill mill, said Dr. Andrew Kolodny, chief medical officer of Phoenix House, a New York-based drug treatment provider. Government regulators should do more to monitor prescribing patterns and intervene proactively if they appear aberrant, he said.

“We wait ’til these doctors kill people,” said Kolodny, founder of Physicians for Responsible Opioid Prescribing, which advocates for tighter regulation of painkillers. “It doesn’t make any sense.”

Medicare’s drug program, known as Part D, now covers about 38 million seniors and disabled people and pays for more than one of every four prescriptions dispensed in this country. Concerns about oversight of controlled substances date back to at least 2011, when the Government Accountability Office highlighted abuse of opioids in Part D and called on Medicare to take action.

Within the past year, Medicare has started to use prescribing data to identify potentially problematic doctors, as have some state medical boards. Beginning in mid-2015, Medicare will have the authority to kick doctors out of the program if they prescribe in abusive ways.

“It’s a real area of concern for us,” said Dr. Shantanu Agrawal, director of the Center for Program Integrity within the federal Centers for Medicare and Medicaid Services.

The 2012 data shows the upward trend line for prescriptions of controlled substances before these initiatives took hold.

The DEA classifies certain potent drugs based on their potential for abuse and sets limits on prescribing for each group. Drugs classified as Schedule 2 require written prescriptions and cannot be refilled. (Doctors may give patients up to a 90-day supply by writing additional prescriptions during a visit.) Prescriptions for Schedule 3 drugs, which are somewhat less addictive, can be phoned in and refilled up to five times.

The DEA says it does not have the resources to track physicians’ prescribing, and instead focuses on drug distribution. So it falls mostly to state medical boards, Medicare and law enforcement agencies to make sure doctors follow the rules for controlled substances. And they have typically relied on complaints, rather than data analysis, to trigger investigations.

ProPublica reported in 2013 that Medicare did not proactively analyze its prescribing data or take action against providers whose patterns were troubling, even if they had been charged with Medicare fraud or kicked out of state Medicaid programs. Most of Medicare’s top prescribers of Oxycontin in 2010 had legal or disciplinary actions filed against them; nonetheless, many retained the ability to prescribe in Part D, as of May 2013.

Shelinder Aggarwal’s Medicare prescribing history had plenty of red flags. The pain medicine specialist has consistently shown up in Medicare’s data as a top prescriber of narcotics. By 2012, the year before he stopped practicing, more than 80 percent of his Medicare patients received at least one prescription for a Schedule 2 drug, in many cases oxycodone. On average, all Alabama doctors in Aggarwal’s specialty issued prescriptions for Schedule 2 drugs to just 38 percent of their patients.

It took complaints from pharmacies near Aggarwal’s office to alert the Alabama Board of Medical Examiners to his unusual prescribing habits, said Larry Dixon, the board’s executive director. Board investigators subsequently made undercover visits to the doctor’s office and videotaped him prescribing drugs without an exam.

“If you paid $1,200 in cash, they would put a VIP stamp on your medical records and you didn’t ever have to have an appointment,” Dixon said.

Medicare’s Part D data draws a roadmap to the doctors who prescribe controlled substances most frequently.

Note: Counts include initial prescriptions and refills dispensed. Retail price includes patients’ out-of-pocket costs but does not reflect drug maker rebates.

In 2012, 269 providers wrote at least 3,000 prescriptions for Schedule 2 drugs, ProPublica’s analysis shows. They were concentrated in a handful of states. Florida led the country with 52 providers, followed by Tennessee with 25. North Carolina, Ohio, Georgia, Pennsylvania, Alabama and Kentucky each had more than 10. (Look up your doctor using our Prescriber Checkup tool.)

About one in five doctors who wrote at least 3,000 prescriptions for Schedule 2 drugs have faced some kind of sanction or investigation, ProPublica found.

In September, Medicare sent 760 letters to doctors who prescribed far more Schedule 2 drugs than others in their medical specialty and state. Officials hope the initiative will cause doctors to examine their prescribing and make changes.

“Simply being an outlier doesn’t establish that you’re doing something wrong,” said CMS’ Agrawal. “What we are trying to do is give physicians the ability to assess themselves, given their comparative data.”

Medicare also has sent information on 71 prescribers for possible investigation to the inspector general of the U.S. Department of Health and Human Services, and on one doctor to a state medical board.

Some medical licensing boards are also expanding their efforts to use data to spot problematic prescribing. North Carolina’s medical board has proposed new regulations allowing the agency that runs the state’s prescription drug monitoring program to share data with the board. The board currently can only access the data when it is pursuing an active investigation into a particular physician.

“We’re just trying to get ahead of the curve here and identify these folks further upstream instead of waiting until there’s an accidental poisoning death or some other type of patient harm that we learn about after the fact,” said R. David Henderson, the board’s executive director.

Similarly, Alabama’s legislature recently authorized its medical board to regulate pain medicine clinics and proactively access data from its prescription monitoring database.

Dixon, the Alabama board’s executive director, and Henderson said their states’ changes are not meant to impede legitimate care by doctors.

“Most of these people are just as genuine as you could possibly hope,” Dixon said.

Data, alone, can be misleading. Athens, Georgia pain specialist Mark Ellis was the third-highest prescriber of Schedule 2 drugs in the country in 2012, with more than 10,000 prescriptions. But unlike many states, Georgia does not allow nurse practitioners and physician assistants to write prescriptions for these controlled substances on their own, requiring them to be signed by a physician. As a result, Ellis said he was credited with the prescribing of four other professionals in his practice. (Ellis was fined by Georgia’s medical board in July 2005 for working with a physician assistant without consent from the board.)

With scrutiny of painkiller prescribing on the rise, Ellis said he attempts to ensure that patients are taking, not selling, their pills by requiring frequent drug testing. “Our practice policy is to monitor all patients every visit, every time they come in, to make sure they’re compliant with their treatment program,” he said.

Rules put in place by several states have reduced prescribing of narcotics, experts say. New York, Kentucky and Tennessee now require that doctors check databases that track every controlled substance prescription in their states before prescribing such drugs to patients for the first time and at certain intervals afterward. Other states are considering or are in the process of implementing similar rules. Such checks are currently voluntary in most states.

Without taking this step, doctors “are woefully unaware of what’s really going on with their patients, and they are unable to discern when they should check. So they make prescribing decisions blindly,” said John Eadie, director of the Prescription Drug Monitoring Program Center of Excellence at Brandeis University.

Mandatory checks are “the most-effective single tool we’ve found yet to address this problem,” he said.

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