"The U.S. has encountered over 200 new substances over the past four years," Scherbenske explained. "Our chemists are finding multiple drugs, multiple compounds when we make purchases of these drugs."
And that means there's no standard when it comes to these drugs.
"When we buy these substances and send them to the lab, they could have one compound in it, or they could have five separate compounds."
The combination of those compounds and their reactions "is very scary," Scherbenske said.
"We do not know the long term effect that it will have on a person's body."
Emily Bauer went from being a normal 16-year-old to nearly dying after trying a form of synthetic marijuana packaged as "potpourri" that she bought with her friends at a gas station. Her family believes the drug is what caused her to have several strokes, which have limited her physical and mental abilities.
Synthetic drugs also have "unpredictable effects on human behavior," according to Dr. Paul Adams, who works in an emergency room in Miami.
"This is a terrible drug because it takes a combination of methamphetamine, and the paranoia and the aggressiveness, and LSD, the hallucinations, and PCP, the extreme paranoia that you get, (and) combines it into one," Adams explained.
Police in Panama City, Florida, reported two violent incidents linked to use of bath salts in 2011. In one, a woman allegedly tried to behead her 71-year-old mother; in the second, a man on bath salts used his teeth to tear up the back seat of a patrol car.
That's particularly troublesome when some retailers are marketing synthetic drugs as a safer, legal alternative.
Who is making this stuff?
Most of the chemicals that are used to make these synthetic drugs are coming directly from China, according to the DEA's John Scherbenske.
"They ship the bulk product here in the United States, where we have individuals that will take that product and package it for retail distribution," he explained.
According to a recent article in Time magazine, the drugs come mostly from "suburban laboratories around Chinese port cities ... from where they can be easily shipped to Europe or North America using regular international courier services."
They're also available in larger quantities and sold over the Internet as "research chemicals," according to Time.
The DEA is "in dialogue" with China about the problem, Scherbenske said, without offering specifics.
"We are also in dialogue and conversation with our international counterparts experiencing the same issues that we are in this designer drug problem," he said. "That is one of the ways to fight this problem is through demand reduction and the education of the people who are using these products."
So who's selling it here in the U.S.?
Scherbenske says people are starting their own businesses to sell these drugs once they see the profit potential.
"And they are starting to become organized," he added. "Is it organized crime? Not at this point, but they are figuring out ways to work around our laws. They are making millions of dollars figuring out how to launder that money. We don't even know if they are paying taxes on this money."
These retailers have even taken the feds to court to protect their business: four stores sued the DEA in 2011, claiming the federal agency was "impeding their business," Scherbenske said.
"We don't have a problem with people selling legitimate items. But when you are selling basic rat poison to our children, we do take issue with that."