The United Nations is sound the alarm over a sharp rise in the amount and variety of “designer drugs”, which are hitting the world’s drug markets faster than governments can ban them.

With harmless-sounding street names such as “spice”, “meow-meow”, and “bath salts”, the known number of these New Psychoactive Substances (NPS) has jumped by more than 50 percent in less than three years to 251 by mid-2012, according to the UN Office on Drugs and Crime.

“This is an alarming drug problem - but the drugs are legal,” according to the UN report, “Sold openly, including via the Internet, NPS which have not been tested for safety, can be far more dangerous than traditional drugs.”

Even when authorities become aware of an emerging designer drug, the illicit drug makers employ their own scientists to slightly modify the molecular structure of a new drug in order to get around prohibition.