THE rate at which new "legal highs" are flooding the drugs market in Europe continues to rise, an EU drugs agency has said, as open sale of the substances online increases their availability.

A total of 81 new psychoactive substances, also known as legal highs or designer drugs, were reported for the first time in 2013, up from 73 the previous year, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) said in its 2013 report.

Europe's Early Warning System, a detection mechanism described as the "first line of defence against emerging drugs", is struggling to cope with the rate at which new synthetic drugs are emerging, the EMCDDA warned. The agency said the UK's average mortality rate due to overdose was 38.3 per million population, more than twice the European average fof 17 per million.