Here's what caused the New York City 'zombie' outbreak

An uncommon drug caused a "zombie" outbreak in a New York City neighborhood this past summer, and now a new report identifies the exact compound that the affected people took.The report also shows scientists how they could identify other such drugs in the future.

The mass intoxication was caused by a type of synthetic marijuana, The New York Times reported at the time. The new report specifically identifies the chemical in the drug product as "AMB-FUBINACA," and also highlights some of the unique difficulties that arise in the study of synthetic drugs.

It's not entirely clear why the drug, which was sold under the name "AK-47 24 Karat Gold," causes "zombie-like" symptoms, such as a slow response time to questions, and blank stares, said study senior author Roy Gerona, a clinical chemist at the University of California, San Francisco.

Indeed, these "zombie" symptoms are "a little uncommon" for people who take synthetic marijuana, Gerona told Live Science. Typically, the synthetic marijuana compounds found in these "mass intoxications" have more severe effects on people's health, including seizures and kidney damage, he said. But in this case, the only effect observed was the depressant, or "zombie-like," effect, he said.

But that effect appeared to be a potent one, Gerona added.

It's difficult for scientists to determine why particular drug compounds are more potent than others in humans, Gerona said. In the new study, published Dec. 14 in The New England Journal of Medicine, Gerona and his colleagues used lab tests to show that the AMB-FUBINACA compound is more potent than compounds found in other versions of synthetic marijuana. Indeed, lab tests showed that AMB-FUBINACA is actually 85 times as potent as THC (tetrahydrocannabinol), the active compound in marijuana, the researchers wrote in their report. However, these lab tests don't always translate to potency in humans, Gerona said.

"It seems like the effects we're seeing in patients only suggest that [the drug] is potent," Gerona said. But the researchers don't know whether that's because the compound is intrinsically potent or because there was a "misdosing" in the packets of the product that were sold commercially and taken by the people in New York, he said.

Synthetic marijuana is made by spraying assorted chemicals onto plant material. But "misdosing" can result — for example, if someone adds too much of the chemical to the herbal material, Gerona said.

"We couldn't know [about the potency] until we tested the effects in animal models," Gerona said.

But testing in animal models can take a long time, and by then, the particular type of synthetic marijuana may be off the market.

Indeed, the dynamic market for synthetic marijuana compounds — there are thousands of these drugs on the market, and new compounds are being synthesized constantly — makes it challenging to even create tests to look for these drugs, Gerona said.

Normally, drug tests are "targeted," Gerona said, meaning that the tests look for a specific, known compound. In other words, if someone is given a drug test for opiates and they have marijuana in their system, the test won't pick up the marijuana, he said.

But it's much trickier to test for synthetic marijuana because there are so many forms of the drug.

"There are literally thousands of designer drugs, so it's not humanly possible to actually develop a targeted" drug test for all of them, Gerona said.

Testing for zombie chemicals

To find out what chemical caused people to become zombie-like in New York, Gerona and his colleagues used blood and urine samples from eight of the intoxicated people. The researchers applied a technique that collected information on all of the compounds present in each sample.

Usually, if the researchers find that one of the compounds in the samples matches the formula for any type of synthetic marijuana, "that's a tentative identification," Gerona said.

But the problem is that in order to confirm the identification, researchers must match the compound they find in the biological sample to a "commercial reference standard," he said. In some cases, this reference standard could come from a product that's on the market. But if researchers can't find the product on the market, they have to synthesize it themselves, which can take months and is very expensive, he said.

To get around this problem, Gerona and his colleagues have synthesized a number of compounds that they call "prophetic synthetic cannabinoids," or new versions of synthetic marijuana that they think will eventually show up on the market.

In this particular case, the researchers found that a metabolite of AMB-FUBINACA, or a compound formed when the body breaks down the drug, was a match with one of their "prophetic" compounds, Gerona said.

Originally published on Live Science.