The substance NRG-1, a so-called legal high, should be made illegal, the Advisory Council on the Misuse of Drugs (ACMD) has said.
It advised the government that the chemical naphyrone, which is sold as NRG-1, should be made a Class B drug.
The ACMD said the drug could "cause real harm due to its potency and associated health effects".
The body also urged the home secretary to impose an immediate import ban on naphyrone in its recommendations.
Prof Les Iversen, who chairs the ACMD, said: "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."
Meanwhile, research published in the British Medical Journal suggests many substances sold legally contain similar ingredients to mephedrone, which was banned in April, and pose health risks.
Researchers bought 17 drugs from 12 UK-based websites over a six-week period after mephedrone became a Class B drug.
They found these substances tend to contain the same substance or related chemicals.
Mephedrone, which was also known as Meow, Bubbles and M-Cat, is made up of a compound class called cathinones.
Experts from Liverpool John Moores University, the University of Liverpool and Lancaster University, said many drugs being sold legally are also cathinones.
Writing in the British Medical Journal (BMJ), they said NRG-1 products, also known as Energy 1 or naphyrone, were found to be "recently banned cathinones that just carried a new label" following chemical analysis.
The researchers went on: "This suggests that both consumers and online sellers are, most likely without knowledge, at risk of criminalisation and potential harm.
"This has important health and criminal justice consequences that will require carefully thought out responses and further investigation."
And Simon Brandt, senior lecturer in analytical chemistry at John Moores, said: "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% contained mephedrone or mephedrone-related products. When we analysed these white powders we found cathinones, related products or a mixture."