Experts say many of these new synthetic drugs don’t show up on blood tests, making it more difficult for medical professionals to identify an overdose.

Over the course of two days in mid-August, more than 95 people in New Haven, Connecticut, overdosed.

Their drug, however, wasn’t heroin. It was synthetic cannabinoids, commonly sold as K2, Spice, or potpourri.

The fallout from the incident was so widespread that experts have referred to it as a “mass casualty incident.”

More than that, it has become a symbol of the dangers of a class of drugs that officials in the United States have little understanding of and even less control over.

In nearby Baltimore, a new study by the University of Maryland’s Center for Substance Abuse Research (CESAR) published this month articulates many of the problems with identifying and treating synthetic cannabinoid overdoses.

Researchers studied urine samples of patients with suspected synthetic cannabinoid overdose at two different hospitals, the University of Maryland Medical Center Midtown Campus in Baltimore and the University of Maryland Prince George’s Hospital Center in Cheverly, a suburb of Washington, D.C.

They almost immediately hit a snag with their study.

If the patients had been using Spice, why wasn’t it showing up in their urine?

“When we got the results back, it was just kind of amazing because we expected to find a large percentage testing positive for the synthetic cannabinoids metabolites we were testing for, and what we found was that in the first go around only I think one specimen testing positive for it,” said principal investigator Eric Wish, PhD, a principal study investigator and director of CESAR at the University of Maryland, College Park, College of Behavioral & Social Sciences.

Despite testing the urine for 169 different drugs, including 26 metabolites of synthetic cannabinoids, it simply wasn’t there.

The issue, say experts, highlights an urgent need for improved testing for so-called new psychoactive substances, including Spice and synthetic cathinones, also known as bath salts.

These new drugs don’t show up on standard drug tests, making it difficult to form a clear diagnosis.

Designer drugs continually manage to dodge legislation because whenever a certain variety is outlawed based on its chemical structure, a new similar chemical is manufactured and sold legally.

“While the press and the media talk about Spice and K2 like it’s a single type of phenomenon, the truth can’t be further from that,” Wish told Healthline. “Basically what you have is some chemist in another country, oftentimes the DEA says it’s China, who waits and they see what has been put on the prohibited list by the government. And then they go ahead and they tweak the molecule a little so it’s no longer on the prohibited list and then they make it available.”