A new UN report warned that new drugs marketed as "legal highs" and "designer drugs" are emerging fast and in great numbers, and authorities are struggling to keep up.
So-called new psychoactive substances (NPS), often sold under harmless names like spice, bath salts or herbal incense, posed a serious health risk although they were legal, the UN office on drugs and crimes (UNODC) said in its annual World Drug Report.
"Sold openly, including via the Internet, NPS, which have not been tested for safety, can be far more dangerous than traditional drugs," it warned.
From 166 known NPS in 2009, the number rose to 251 in 2012, according to the UN body.
These drugs, which could be synthetic or plant-based and could be easily altered to create new ones, were now outpacing efforts to control or ban them, it said.
"The international drug control system is floundering for the first time under the speed and creativity of the phenomenon," the UN deplored.
The perception that the drugs were safe also compounded the problem, it said, adding that the long-term effects were unknown.
In the United States, NPS were the most used drugs among students, after cannabis. In Europe, NPS use was on the rise, even as cannabis use has gone down and consumption of other drugs has remained steady.
New psychoactive substances were also present in Asia and Africa and with an ever-growing number of drugs to control, national health, customs and police authorities were stretched thin, requiring more international cooperation to detect them, the UNODC appealed.
Worldwide, cannabis was still the most commonly used illegal drug with 3.9 percent of the global population aged 15-64 using it, the report said.
In 60 percent of countries however, prescription drugs like sedatives and tranquilisers were among the top three misused substances, which was "of particular concern," it added.
The market for amphetamine-type stimulants (ATS), which include ecstasy and methamphetamine, was also growing, especially in east and southeast Asia, the UNODC found. Ecstasy was on the rise in Europe.
Meanwhile, eastern and western Africa were becoming increasingly important to traffickers.
A new maritime route seemed to have developed from Afghanistan through Iran and Pakistan leading south towards Africa, "a worrying trend" given the lack of trafficking information on that continent, the UNODC said.
"Africa is increasingly becoming vulnerable to the drug trade and organized crime," UNODC chief Yuri Fedotov warned.
With US-led NATO troops due to leave Afghanistan in 2014, Fedotov also urged "concerted efforts" to help curb drug production in the war-torn country. Last year, Afghanistan produced 74 percent of the world's opium, according to the UNODC.