In the U.S., these NPS's were the second-most used substances among young people, after pot. In Europe, the drugs' use was most prevalent in Poland, the U.K., Latvia, and Ireland, where more than 8 percent of people between the ages of 15 and 24 said they've tried them.

The drugs' newness apparently makes them seem much safer than they actually are: Ketamine, for example, can cause heart and lung failure. The synthetic drug known as "bath salts" has been known to induce "rabid-animal behaviors like biting, kicking, and primal viciousness."

"This is an alarming drug problem -- but the drugs are legal," the UNODC said. "Sold openly, including via the Internet, NPS (new psychoactive substances), which have not been tested for safety, can be far more dangerous than traditional drugs."

The report noted that the drugs often originate in East and South Asian pharmacies. Trying to regulate them is like playing a perpetual game of whack-a-mole, since the narcotics' altered molecular structures mean they don't fall under international bans. In 2012, the U.S. Congress added 26 of these drugs to the Controlled Substances Act, but their makeup keeps changing rapidly to elude regulations.

When brought under control in one country, production and/or the distribution centres of these substances are shifted to another country so that the sales -- often conducted via the Internet -- can continue.

The agency noted that there were 693 online shops for buying NPS's in January 2012, up from 170 in 2010. The report noted that popular trafficking routes have also started developing through the Middle East and Africa, and the profits often end up in the hands of terrorists.

Beyond the public health angle, this is also an interesting case study in the challenges law-enforcement groups face in trying to make international regulations keep pace with chemistry. Some national and state laws prohibit many of these drugs, but it can be hard to keep up even for the most determined of drug-busters:

"As soon as we make these things illegal, criminal organizations will go back and change one molecule... one molecule and it changes the entire drug. It changes the whole structure of the drug, so the drug becomes legal and we're at it again," James Capra, the DEA chief of operations told ABC. "And that's the dynamic of what we're faced with."