More than 600 so-called "legal highs" have been detected as new drugs continue to flood into circulation, a major report has revealed.
A United Nations monitoring body had identified 602 unique new psychoactive substances as of October.
The tally - based on reports from member states - was a 55% increase from the 388 recorded at the same point in the previous year.
The International Narcotics Control Board described NPS as a "growing threat" and "a very heterogeneous group of substances that, in different forms, continues to grow in every region of the world".
Its annual report for 2015 said: "Governments acknowledge the complexity of dealing with an ever-changing spectrum of substances made especially to circumvent controls.
"In most cases, such substances have unknown short- and long-term effects and may have highly addictive and toxic profiles.
"A growing number of those substances are now being manipulated and peddled to people, especially youth, at the expense of their health.
"It is therefore a matter of health and welfare to ensure that those substances are kept away from potential users and that the targeted population groups are provided with information on the risks associated with such substances and primary prevention services."
Seizures of new psychoactive substances increased seven-fold across Europe between 2008 and 2013, the report said.
It added: "The increase in the trafficking and abuse of those substances continued to pose a public health challenge in many European countries."
The emergence of legal highs in recent years has sparked concern around the world.
In Britain the Government has introduced legislation to ban the production, distribution, sale and supply of the drugs after they were linked to several deaths.
The INCB report also identified the United Kingdom, along with Denmark and France, as being among the EU countries with the highest lifetime prevalence of drug abuse among the general population.
Last year separate analysis indicated that Britain has the highest rate of cocaine use among young adults in Europe, with figures for 2013/14 showing that around one in 24 people aged between 15 and 34 admitted taking the drug in the last 12 months.
The new study also said the purity and potency of all the drugs of abuse commonly found in western and central Europe have increased.
"The reasons for that increase are complex, and may include advances in technology and market competition," the report said. "In some countries that produce high potency cannabis, the share of that substance on the domestic market has increased in recent years. New data indicate that the potency of cannabis resin smuggled in the region has also increased."
Europe remains a key market for drug traffickers, according to the INCB, which added that the internet and social media have become "important tools" in the marketing of drugs.