Rise in deaths from 'legal highs' in the UK
12 February 2014 Last updated at 09:40 GMT
The number of UK deaths linked to so-called "legal highs" has risen in recent years - from 10 in 2009 to at least 68 in 2012, figures show.
Researchers compiled post-mortem test results for the National Programme on Substance Abuse Deaths.
Tulip Mazumdar reports.