UK legal high market is EU's largest, UN report says
26 June 2013 Last updated at 19:32 BST
The UK has the largest market for so-called "legal highs" in the European Union, according to the United Nations Office on Drugs and Crime (UNODC).
A total of 670,000 Britons aged 15-24 have experimented with the substances at least once, it says in its 2013 World Drug Report.
It says there has been an alarming increase worldwide in new psychoactive substances, known as NPS.
The UK's crime prevention minister said the UK was addressing the threat.
Sarah Campbell reports.