US and European authorities are fighting a new enemy in the war on opioids. Nitazene is a class of synthetic drugs 40 times more potent than fentanyl that has caused hundreds of confirmed deaths across Europe and the US since appearing on the radar of law enforcement agencies in 2019. However, this figure is likely to be a significant undercount.

Nitazene was first synthesized in the 1950s by CIBA Aktiengesellschaft, an Austrian chemical company, which created several chemically related molecules with varying levels of painkilling power. However, their use as pain relievers never declined. In addition to being highly addictive, nitazene can cause respiratory depression, a dangerous condition where breathing becomes too shallow to replenish oxygen in the blood. So these drugs were largely unheard of for decades until they appeared on the illegal market.

It’s hard to say exactly when nitazene became commonly sold as a street drug—identifying it requires specific tests that aren’t routinely performed—but law enforcement agencies began noticing it about six years ago. A shipment of one type of these synthesized molecules — isotonitazene — was intercepted in the American Midwest in 2019, and deaths were reported in both the US and Europe in the following years.

Drug makers and dealers were probably attracted to nitazenes because of their potency and because they have similar effects to better known drugs such as heroin. This makes them useful substances for dealers, as they can use them to cut other opioids to make their drugs go further, increasing the volume they can sell. This poses serious risks to users, who are often unaware of what they are actually taking, increasing the threat of overdose.

The other attractive feature of nitazene was that authorities forgot about it: A drug with less attention, as well as an ill-defined legal status, is easier to trade. It is believed that illegal laboratories began synthesizing nitazene using historical chemical formulas found in pharmacology textbooks, as well as developing new formulas.

In the US, nitazene is now widespread in most of the country and is manufactured in Mexico or within the country in illegal laboratories supplied with raw materials by Asian traffickers. Synthetic opioids are the most problematic drug in the US — accounting for about 70 percent of the 105,000 overdose deaths recorded in 2023 — and of these, fentanyl is the most common. But nitazene, while still a minority drug, is rapidly becoming more common.

Europe, for its part, has always been a market dominated by heroin, with almost everything coming from Afghanistan. However, when the Taliban regained power in Afghanistan in 2021, it banned the cultivation of the opium poppy, thus cutting off the source of the raw material used to create heroin destined for Europe. As opium supplies run out, it is possible that there will be a shortage of heroin in the European market that synthetic opioids can fill.