Nitazenes were created over half a century ago as pain medication but they were never approved for use in the US.

One called protonitazene is about three times more powerful than fentanyl, while isotonitazene is 10 times as strong.

According to Alex Krotulski, associate director at the Center for Forensic Science Research and Education in Pennsylvania, nitazenes have become the “most popular subclass of new synthetic opioids,” and are “way more potent than fentanyl, which is really scary.”

There are fears that Narcan, which is used to reverse overdoses, may not be as effective with the new class of drug.

Alexandra Evans, a forensic chemist who picked up the presence of nitazines in Washington, said: “We could be on the precipice of something devastating.

“We’ve already seen mass fatalities because of fentanyl overdoses. Since this is more potent than fentanyl we do expect an uptick in overdoses.”

Nitazenes are believed to have contributed to a surge in deaths in the capital, with nearly 500 fatal overdoses in the last year.

Across the US drug overdoses are now responsible for more deaths than car crashes, guns, flu and pneumonia.

According to the Centers for Disease Control and Prevention 100,300 Americans died of drug overdoses between May 2020 and April 2021.

The states with the largest increases – all up over 50 per cent – were Vermont, West Virginia, and Kentucky.

Fentanyl surpassed heroin five years ago as the drug involved in the most overdose deaths.

Drug cartels in Mexico use chemicals from China to mass produce and distribute fentanyl across America, and the drug is also bought and sold on the dark web.

Dealers have mixed fentanyl into other drugs, including methamphetamines and cocaine, which has led to more fatalities.

With nicknames including “Poison” and “Drop Dead” it is 50 times stronger than heroin, and is mixed in to increase that drug’s potency.

So far in 2021 the Drug Enforcement Administration has seized a record 12,000 pounds of fentanyl.
Experts who track the illegal drug supply in the US said new more powerful synthetic opioids were turning up at an alarming rate.

Morgan Levitas, a chemist at Washington’s forensic sciences department, said: “Every few weeks, we’re seeing something that we haven’t seen before. You can definitely see that there’s consistent changes in the drug supply here.”