"Fentanyl, heroin, and some prescription painkillers (such as morphine and oxycodone) belong to the class of drugs known as opioids, which act on receptors in the brain important in regulating pain and emotion. Opioids have susceptibility for abuse and potential for overdose. In 2016, more than 42,000 of the nearly 64,000 drug overdose deaths in the United States involved opioids. Led by fentanyl, a synthetic opioid 50-100 times more potent than morphine, synthetic opioids emerged as the leading cause of opioid-related overdose deaths in 2016. The steep increase in deaths involving fentanyl is seen as a 'new chapter' in the opioid epidemic."
CRS Insight, IN10914