Overdose deaths involving heroin and fentanyl are spiking, while deaths due to prescription opioids are declining, new research concludes.

A study from the American Action Forum found the annual growth rate of all opioid-involved overdose fatalities rose from 9.1 percent before 2010 to 12.3 percent after 2010. The annual growth rate of overdose deaths involving heroin increased from 4.1 percent before 2010 to 31.2 percent after 2010. The annual growth rate of overdose deaths involving synthetic opioids such as fentanyl also increased, from 13.7 percent to 36.5 percent.

The study found that as authorities cracked down on the overprescribing of opioid painkillers, international drug cartels filled the void by supplying cheap heroin and synthetic opioids such as fentanyl, according to The Washington Post.