For anyone who does not already realize that fentanyl ranks among the deadliest and most devious drugs out there, the Department of Homeland Security would like to underscore the point.

Task & Purpose snagged an internal memo about the department looking toward deeming the synthetic opioid a weapon of mass destruction “when certain criteria are met.”

In fact, the drug is so lethal that Homeland Security fears terrorists getting their hands on fentanyl and somehow using it as “a viable option for a chemical weapon attack by extremists or criminals,” according to James F. McDonnell, DHS assistant secretary for countering weapons of mass destruction.

As to the veracity of all this, a Homeland Security official tells The Post, “DHS is constantly assessing new and emerging threats that may impact the nation’s security. We coordinate closely with partners at DOD, DOJ and throughout the interagency to better protect the American people. We will not comment on the specifics of these discussions.”

Legally, fentanyl is most commonly employed to treat the unbearable pain brought on by cancer. Illegal forms of the drug — often originating in China or Mexico — are frequently mixed with heroin to spike up the potency. That makes the narcotic stronger but also deadlier. According to a government report quoted by CNN, fentanyl is “the most commonly used drug involved in drug overdoses” and contributed to nearly 29 percent of American overdose deaths — totaling 18,355 — in 2016.

Nevertheless, there are those who maintain that McDonnell — he suggested that “new technologies” can be viable for battling the scourge on a federal level — might be getting carried away with his concerns.

One expert likened the move to “declaring ecstasy as a [weapon of mass destruction],” Task & Purpose reports. Another described the likelihood of fentanyl being used by terrorists as a “fringe scenario.” He pointed out that there are other easier, equally deadly options for killing large numbers of people.

While McDonnell has reportedly stated that “senior leaders” are on board with his plan, not everybody has bought in. Task & Purpose quotes an anonymous official saying, “I cannot see any scenario where a nation-state would use fentanyl on a battlefield or . . . an attack when they could just sell it for funding the purchase of . . . firearms and explosives” — and they’ll have the side benefit of causing American drug deaths in the process.