A lethal dosage of 2 milligrams of fentanyl can be lethal for most people, the agency said.
Fentanyl is a powerful opioid that is 50 to 100 times more potent than morphine and 30 to 50 times more potent than heroin. Though fentanyl can be prescribed by a physician for pain relief, the vast majority of overdose cases are thought to be the result of illicit production and distribution.
Synthetic opioids such as fentanyl are the No. 1 killer in the opioid epidemic, according to a report released this month.
The report, published in the journal JAMA, found that fentanyl-related deaths more than tripled between 2010 and 2016.