Government letters informing doctors they're prescribing vastly more addictive drugs than their peers fall on deaf ears, according to a new study.

The doctors in the study were all writing far more prescriptions for drugs like opioid painkillers than doctors in similar specialties practicing nearby - but the letters didn't lead to changes in prescribing.

Still, the study's lead author said the results will help researchers who are studying ways to get doctors to pay attention.

"I think if there is a way to make these letters effective it may be one tool in the arsenal to curb the high rate of opioid deaths," said Adam Sacarny, of the Mailman School of Public Health at Columbia University in New York City.

The use and abuse of opioid pain relievers - like Vicodin and OxyContin - have risen dramatically since the late 1990s, with overdose death rates quadrupling between 1999 and 2014, the researchers write in Health Affairs.

They point out that seniors are often prescribed benzodiazepines or "benzos" - like Xanax and Valium - for long periods of time, but these drugs can increase their risk for falls.

Previous research on the effectiveness of letters has found that comparisons to peers can encourage doctors to vaccinate their patients and people to pay their taxes, Sacarny told Reuters Health.

To see if letters could do the same for the overprescription of addicting drugs, the researchers used 2011-2013 data from Medicare, the joint federal and state health insurance program for seniors and the disabled.

They identified 1,525 outlier healthcare providers prescribing Schedule II controlled substances, which carry the potential for abuse and dependence, at much higher rates than their peers. The providers were prescribing under the program's prescription program known as Medicare Part D.

An average outlier provider was responsible for 406 percent more prescription drug fills than comparable peers, who were matched by state and specialty.

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About 60 percent of the providers were general practitioners. Another 20 percent were nurse practitioners, and only 20 percent were specialists.

In 2013, the average outlier provider was each tied to about 1,444 Schedule II prescriptions, which adds up to almost $200,000.

The outliers were randomly assigned to two groups. In September 2014, providers in one group received letters from the Centers for Medicare and Medicaid Services (CMS) informing them of how much more they were prescribing addicting drugs in relation to their peers across the state and nation.

After 90 days, there were no significant differences in prescribing patterns between the group that received the letter and the group that didn't.

It's possible the letters didn't reach the providers or that the letters just weren't effective, according to the research team, which included people from CMS in Baltimore, the Massachusetts Institute of Technology in Cambridge and the White House Social and Behavioral Sciences Team in Washington, D.C.

Sacarny said a new trial is looking to see whether letters can affect the prescribing of the antipsychotic medicine quetiapine - marketed as Seroquel by AstraZeneca. The letters in the new trial will be sent several times and will emphasize the negative consequences of overprescribing.