A drug used on the gay clubbing scene should be banned, the Advisory Council on the Misuse of Drugs (ACMD) has said.
NRG-1, which is made from the chemical naphyrone and is similar to mephedrone, is a legal high but should be made a class-B drug, the ACMD advised.
The body said the substance could cause “real harm” and urged home secretary Theresa May to place an immediate ban on its import.
Other previously-legal highs which are now banned include mephedrone, Spice, GBL and BZP.
ACMD chairman, professor Les Iversen, said: “Naphyrone is a drug with the potential to cause real harm due to its potency and associated health effects.
“Users of ‘legal highs’ should be aware that just because a substance is being advertised as legal does not make it safe, nor may it be legal.
“Test purchasing has demonstrated that what you think you are buying is often not what is in the packet. The harms and effects of your purchase may be different and or greater than you expect.”
The report said that NRG-1 could cause problems with the heart and blood vessels, hyperthermia, dependence and psychiatric effects.
It also cited evidence from a recent study published in the British Medical Journal which suggested many drugs being sold as NRG-1 were mislabelled and contained illegal compounds.
The research was carried out by Liverpool John Moores University, the University of Liverpool and Lancaster University.
Simon Brandt, senior lecturer in analytical chemistry at John Moores, told BBC News: “The analysis showed that those sold as legal alternatives turned out to be related to mephedrone and some of them were just, in fact, mephedrone.
“About 70 per cent contained mephedrone or mephedrone-related products.”