The diversion and abuse of prescription painkillers decreased slightly between 2011 and 2013, after increasing substantially from 2002 to 2010, according to a study in this week’s New England Journal of Medicine. The findings suggest the U.S. may be making progress in controlling prescription opioid abuse, the researchers say.

The study also found heroin abuse and overdoses are increasing, HealthDay reports.

The findings come from data from five drug-monitoring programs. Four of them reported a pattern of declining prescription opioid abuse, the article notes. The programs tracked the diversion and abuse of six prescription opioid analgesics: oxycodone, hydrocodone, hydromorphone, fentanyl, morphine, and tramadol. The programs gather data from drug-diversion investigators, poison centers, substance-abuse treatment centers, and college students.

“The big ‘but’ is heroin abuse and overdose, which is increasing,” said lead author Richard Dart, Director of the Rocky Mountain Poison and Drug Center in Denver. “It’s a good news/bad news story,” he said. Dart noted part of the decline in prescription opioids is due to some users switching to heroin.

The rate of heroin-related deaths increased from 0.014 per 100,000 in 2010 to more than 0.03 per 100,000 in 2013, the researchers found.

Dart said the decline in prescription opioid abuse is also partly due to legislation on the federal, state and local level. He noted states have implemented prescription drug monitoring programs to detect “doctor shoppers,” who visit multiple physicians in an attempt to obtain prescriptions. In addition, medical groups have issued guidelines on painkiller prescribing designed to limit inappropriate use.