NEPTUNE — Monmouth County authorities have discovered the often-deadly cyclopropyl fentanyl for the third time this year — this time in what appeared to be legitimate Oxycodone pills.

Fentanyl — a drug about 50 to 100 times more powerful than morphine — has been at the heart of New Jersey's opioid overdose epidemic. It's often used to lace heroin, but increasingly being sold on its own.

Authorities have warned that analogues like cyclopropyl fentanyl and the increasingly common carfentanil — the latter being as much as 10,000 times as strong as morphine, only legitimately intended as an anesthetic for large animals, like elephants — can be far more deadly. A single granule can kill.

According to biotech company Cayman Chemical, the toxic effects of cyclopropyl fentanyl on human and animals aren't yet fully known.The prosecutor's office said it's not intended for humans, and has been linked to a rash of fatal overdoses across the country earlier this summer.

“Persons buying these drugs on the black market are in grave danger. This substance is lethal.” Monmouth County Prosecutor Christopher J. Gramiccioni said in a statement released Tuesday night.

According to the prosecutor's office, earlier this year, Neptune Township Police seized 30 suspected Oxycodone pulls during an investigation at the Crystal Inn. They were initially thought to be legitimate, pharmaceutical pills before the cyclopropyl fentanyl was discovered.

Earlier this month, the prosecutor's office said, authorities siezed similar pills in Long Branch and Holmdel. Those wre marked A/215, just like real Oxycodone tablets.

“No one should be buying drugs in an illicit manner, but it’s important to know how to distinguish the deadly phony drugs from the real thing. These pills look and feel only slightly smaller and the coloring is off by just a shade," Gramiccioni said. "It bears repeating: If you are buying these pills on the street, you are playing a deadly version of Russian roulette"

He called the arrival of carfentanil and cyclopropyl fentanyl in New Jersey "a tragic development in the opiate crisis we are already facing — especially for those suffering with an opiate addiction in Monmouth County.