As if America’s opioid addiction epidemic could get any worse, black market drug lords have begun to lace heroin with carfentanil, a synthetic opioid humans normally use to tranquilize elephants. This, its intended use, says everything you need to know about the drug: It’s strong as fuck. Carfentanil, already responsible for hundreds of deaths across the U.S., represents the inevitable next step in the never-ending competition to create the most potent high. It certainly won’t be the last.

A year ago, drug enforcement agents across the United States were just beginning to test the word “fentanyl” on their tongues. Today, it’s part of common parlance, largely because the super-opioid was blamed for the death of rock legend Prince. Carfentanil is the latest mouthful of syllables to take its place.

Chemically speaking, the two drugs are closely related: Carfentanil is an analog of fentanyl, meaning that the chemical structures of the two drugs are pretty much identical, besides a few minor tweaks to the outlying branches. In this case, said tweaks are responsible for a spike in potency that makes carfentanil 100 times stronger than its already-murderous cousin. For scale: Fentanyl is some 80 times stronger than morphine, making it so potent that it gave SWAT officers raiding a fentanyl den a literal contact high — a severe one, at that — through their skin. Carfentanil makes fentanyl look like pixie dust: At 10,000 times stronger than morphine, this stuff could kill on contact. And unwitting heroin users, their supply laced with it, take it straight to the vein.

MINNEAPOLIS, MN - APRIL 21: Guests dance to Prince music as a slide show flashes images of the artist above the stage during a memorial dance party at the First Avenue nightclub on April 21, 2016 in Minneapolis, Minnesota. Prince, 57, was pronounced dead shortly after being found unresponsive at Paisley Park Studios in Chanhassen, Minnesota near Minneapolis. (Photo by Scott Olson/Getty Images)
Rock legend Prince is believed to have died from pills laced with fentanyl. Carfentanil, its much stronger analog, is now being used to cut street heroin.

As far as roads toward incapacitation go, the intravenous route is the fastest. That’s why veterinarians attempting to immobilize giant mammals administer Wildnil — the brand-name carfentanil, for massive animals like elephants, moose, and deer — via equally giant needles. Only two milligrams of the stuff is needed to knock out a 2,000-pound African elephant, and even in these giants, carfentanil overdoses have been known to trigger heart attacks and internal bleeding.

When it’s injected into a human vein, death comes quickly: In August, a single city in Ohio saw 96 heroin users die from what appeared to be a heroin overdose, only to find afterward that the drugs they had used were laced with carfentanil. In West Virginia, Kentucky, and Michigan, officials have seen similar spikes in seemingly heroin-related fatalities.

Ultimately, all opiates, their synthetic kin, and cocktails thereof — whether heroin, morphine, dirty Sprite, fentanyl, carfentanil, or whatever new analogs will inevitably make their way onto future streets — kill in the same way. Once they’re in the body, opiates bind themselves within the arms of opioid receptors, which are scattered liberally over the parts of the central nervous system that control breathing, including the brainstem. Lodged there, they slow down breathing patterns and, at higher doses, force users to take shallower breaths. At high enough doses, breathing becomes slower and shallower until it doesn’t happen at all. “Respiratory depression” is a term you hear a lot in clinics and emergency rooms that see opioid users. If admitted early enough — and if they live in the right state — patients could be lucky enough to get an injection of naloxone, a drug that reverses the fatal symptoms of an overdose.

Unfortunately, carfentanil is so strong that the normal doses of naloxone are no longer effective.

So why use carfentanil anyways? It’s generally believed that the synthetic opiates are being used by dealers to stretch their supply and offer users a stronger high. The sad part is, it’s unlikely that users of carfentanil-laced heroin will even get to feel the euphoria they’re promised. With fentanyl and carfentanil, drug producers have seemed to have reached a tipping point: In their endless game of one-upmanship, vying to create the strongest, cheapest high, they have managed to produce effects that are too potent to be experienced. Whether the introduction of fatal mixers to America’s black market opioid supply will mark a turning point in the addiction crisis remains to be seen, but it seems unlikely: Severe addicts will need to be informed of the urgent dangers of carfentanil-laced heroin being sold on the street, and even then, will have no way of testing what they’re using. Besides, like fentanyl, carfentanil will be supplanted: There is no dearth of fentanyl analogs, all of which have strong opioid activity and, owing to their excruciatingly slight differences, are maddeningly difficult to regulate.

In the struggle to manage the ever-escalating opioid addiction crisis, the strategy Canada’s government has begun to employ what might be the best — and only — solution: Legal prescription heroin, administered safely to addicts as part of the rehabilitation process and, crucially, devoid of drugs designed for the bloodstreams of giant animals, not humans.

Photos via Getty Images / Scott Olson

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.