Over the past four years, New York City's elected officials have decried the dangers of the synthetic cannabinoid "K2"and passed legislation outlawing the stuff. The drug, which is often referred to as "synthetic marijuana," has been sold under a variety of street names. It made headlines in July, when hundreds of users overdosed within the span of a few days near the intersection of Myrtle Avenue and Broadway in Brooklyn. "It's zombie land out here," a local resident said at the time.

Now, a new study published in the New England Journal of Medicine has found that the K2 responsible for the Brooklyn overdoses, known as AK-47 24 Karat Gold, was 85 times more potent than marijuana in plant form. This batch of the drug was apparently manufactured in underground Chinese laboratories and was adulterated with a variety of chemicals.

The study was conducted using blood and urine samples taken from eight men hospitalized during the July overdose epidemic. Researchers identified the specific drug as AMB-FUBINACA, a substance originally developed by Pfizer to amplify the medicinal aspects of THC while simultaneously muting its psychotropic effects. Eventually, research work on the drug was halted. It was never tested on humans.

The Times notes, however, that the patent for AMB-FUBINACA is public, and that as as early as 2008, packaged doses of the drug began appearing on the streets in North America and Europe. For years, manufacturers were able to stay ahead of anti-drug legislation by slightly altering the chemical makeup of the compound, keeping K2 technically legal.

Also, included in the medical study is a thorough look at how K2 is sold. The synthetic active ingredients are produced in foreign labs and marketed on semi-secret "dark web" sites. On these sites, a kilogram of powdered AMB-FUBINACA can go for between $1,950 to $3,800. Middlemen drug dealers step on the powder with ground herbs until it reaches a smokeable form. In New York City, mixed K2 is divided into individual bags, distributed to smoke shops and bodegas via wholesalers, and sold for around $5 a packet.

In their new study, medical researchers found that smoking K2 can lead to irregular heartbeat, drowsiness, delirium, seizures, and even death. Throughout the summer, residents living near Myrtle-Broadway observed K2 users behaving manically, urinating in public, shouting, and waving their limbs around erratically. Others fell into a near-comatose state after they smoked, stumbling and falling on sidewalks.

It's a lucrative business. In 2015, federal agents seized bags of K2 with a street value of $10 million at a Bronx garage.

"There is this false idea out there that these drugs are safe, because no one overdoses on marijuana," University of California clinical chemist Roy Gerona told the Times. "No compound that has been made yet has the potential to kill thousands of people. But that is a scenario that is becoming more and more close to reality."