Mexxy will be made illegal for up to 12 months while the Government's drugs advisers decide whether it should be permanently controlled.
It follows concerns that two people whose bodies were found in Leicestershire in February may have taken some form of the drug after buying it over the internet.
Anyone caught making, supplying or importing the drug will face up to 14 years in prison and an unlimited fine under the Misuse of Drugs Act 1971, the Home Office said.
Police and border officials will also be allowed to search or detain anyone they suspect of having the drug and seize, keep or dispose of a substance they suspect is mexxy.
Crime Prevention Minister Lord Henley said: "Making this drug illegal sends a clear message to users and those making and supplying it that we are stepping up our fight against substances which are dangerous and ruin the lives of victims and their families.
"But making drugs illegal is only part of the solution.
"It is important for users of these harmful substances to understand that just because they are described as legal highs, it does not mean they are safe or should be seen as a 'safer' alternative to illegal substances."
Since the drugs was referred to the Advisory Council on the Misuse of Drugs (ACMD) earlier this month, the advisers have presented further evidence that its use can lead to "significant additional toxicity", including agitation, a faster heart rate and higher blood pressure, as well as unsteadiness on the feet.
Such symptoms are rarely seen with ketamine or other recreational drugs, the advisers said.
Professor Les Iversen, chairman of the ACMD, said: "The evidence shows that the use of methoxetamine can cause harm to users.
"Many of the health effects of methoxetamine are similar to those of ketamine, which is already controlled under the Misuse of Drugs Act.
"Users have also reported experiencing other serious effects including agitation, cardiovascular conditions and hypertension."
Police warned people not to take mexxy, which was advertised and sold as a safe alternative to the class C drug ketamine, after the bodies of a 59-year-old woman and a 32-year-old man were found in Leicester and Melton Mowbray on February 11 and 12 respectively.
28 March, 2012
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