VIENNA (Reuters) - A sharp rise in the variety of legal "designer drugs" with names that entice young people into thinking they pose no risk is alarming from a public health standpoint, the United Nations drugs agency said on Wednesday.
The number of new psychoactive substances - marketed as "designer drugs" and "legal highs" - as reported by member states jumped by more than 50 percent in less than three years to 251 by mid-2012, the U.N. Office on Drugs and Crime said.
"This is an alarming drug problem - but the drugs are legal," it 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."
Names including "spice", "meow-meow" and "bath salts" mislead young people into believing they are indulging in low-risk fun, UNODC said.
But "the adverse effects and addictive potential of most of these uncontrolled substances are at best poorly understood", the agency said in an annual survey.
Use of such substances among youth in the United States appears to be more than twice as widespread as in the 27-nation European Union, where the United Kingdom, Poland and France have the most users, it said.
New psychoactive substances can be made by slightly modifying the molecular structure of controlled drugs, making a new drug with similar effects which can elude national and international bans.
They are "proliferating at an unprecedented rate and posing unforeseen public health challenges," said the report that examines production, trafficking and consumption trends.
"The international drug control system is floundering, for the first time, under the speed and creativity of the phenomenon" of this type of substances, the UNODC report said.
Overall, global drug consumption has remained stable, the report said, referring to the number of drug users with dependence or drug-use disorders. In 2011, the number of drug-related deaths was estimated at 211,000.
"While the use of traditional drugs, such as heroin and cocaine, seems to be declining in some parts of the world, prescription drug abuse and new psychoactive substance abuse is growing," it said.
Heroin use in Europe and that of cocaine in the United States appear to be falling while the cocaine market is expanding in South America and the emerging economies in Asia.
The U.N. agency's 2013 World Drug Report also said revised data showed that the prevalence of people injecting drugs who are also infected with the human immunodeficiency virus that causes AIDS was sharply lower than previously estimated.
In 2011, about 1.6 million people between the ages of 15 and 64 who injected drugs were living with HIV, a 46 percent decline since estimates three years earlier. The overall number of people using needles to take drugs was also lower.
The reduced figures are "in large part a result of the availability of more reliable information on HIV prevalence among people who inject drugs", the report said.
Criminals have been quick to tap into the lucrative market of new psychoactive substances while the law lags behind, the U.N. office said. Africa is becoming a target for the trafficking and production of illicit substances, it added.
"East and West Africa seems to be gaining in prominence with regard to routes for maritime trafficking," the report said. Seizures of heroin have risen sharply in Africa since 2009, especially in East Africa, where they increased almost tenfold.
Editing by Michael Roddy