The CDC considers this the third wave of overdose deaths in the growing epidemic, characterized by a surge in synthetic opioid overdoses, following prescription opioid deaths (first wave) and heroin deaths (second wave). The death rate for synthetic opioids doubled to 6.2 per 100,000 people in 2016.

Because fentanyl, a highly potent synthetic opioid, is increasingly mixed with other opioid and benzodiazepine pills, heroin and cocaine, the CDC suspects fentanyl is also contributing to rising death rates among those substances.