Across the UK, 12 people were found dead with the substances in their system in 2009.
The figures increased to 97 in 2012, according to a report.
In about two thirds of cases, the post-mortem established that the
"legal high" was the
direct cause of death.
The figures, which include Scotland, were published in the National Programme On Substance Abuse Deaths report.
Professor Fabrizio Schifano, spokesman for the organisation, said: "The worrying trend is that these type of drugs are showing up more than ever before.
"Clearly, this is a major public health concern and we must continue to monitor this worrying development.
"Those experimenting with such substances are effectively dancing in a minefield."
It is illegal to sell or
advertise so-called legal highs as a "mood-altering substance".
However, suppliers use descriptions such as "plant foods" and "fertiliser" to get around the law.
Victims can suffer
palpitations, anxiety and
severe sickness after
taking the drugs.
The report indicates
an increase in the proportion of deaths involving stimulants such as
cocaine and ecstasy-type drugs.
In total, the number
of drug-related deaths
reported to the National Programme On Substance Abuse Deaths
during 2012 was 1613.