A woman stares at her pain medication.High doses of powerful narcotic painkillers appear to be linked to a higher risk of depression in patients, new research finds.

The study focuses on a class of prescription narcotic painkillers called opioids, which include drugs such as Oxycontin and Vicodin. While most people use the medicines to ease pain, widespread abuse of narcotic painkillers is also a growing concern.

The new study involved 355 patients in Texas who reported low back pain at an initial medical visit and still had the pain one and two years later.

Although the study couldn’t prove cause-and-effect, people who used higher doses of narcotic painkillers to manage their pain were more likely to have an increase in depression, the researchers found.

Learning more about the link between these painkillers and depression, along with what dosage might put patients at higher risk, “may inform prescribing and pain management” by doctors, wrote a team led by Jeffrey Scherrer, an associate professor for family and community medicine at Saint Louis University, in St. Louis.

The findings are published in the February issue of the journal Pain.

After the study was accepted for publication, the investigators continued their research and found “that most of the risk of depression is driven by the duration of use and not the dose,” Scherrer said in a journal news release.

It “could be that the patients who increase dose were the longer-using patients,” Scherrer said. “This is logical, as longer use is associated with tolerance and a need to increase opioids to achieve pain relief.”