Synthetic opioids, some of the most potent drugs, were involved in close to half of all opioid deaths in 2016 and 30% of overdose deaths overall, according to a new study published in the Journal of the American Medical Association.

Between the lines: Prescription drugs had been the primary cause of overdose deaths — in 2011, only 6% of overdose deaths involved synthetic opioids. But now these more dangerous, often illicit drugs, primarily fentanyl, are driving the ever-rising overdose death toll.