Hospital treatment rates for heroin rose more than 31 percent between 2008 and 2014, while treatment rates for prescription opioids have declined, according to a new study.

Hospital discharge rates for prescription opioid poisonings decreased each year by about 5 percent between 2010 and 2014, the study found.

Lead researcher Tina Hernandez-Boussard of Stanford University said the results provide evidence that people addicted to prescription opioids are turning to heroin because it is cheaper and easier to get, HealthDay reports.

“I’m cautiously optimistic that prescribing clinicians are positively reacting to the opioid crisis and therefore prescription opioids are contributing less to the overall drug epidemic,” Dr. Hernandez –Boussard said in a news release.

The findings are published in Health Affairs.