A ban on mephedrone and other so-called "legal highs" was backed by the Lords today amid accusations ministers were guilty of a "knee-jerk" response.
Home Office minister Lord West of Spithead denied the charge from the Liberal Democrats, telling peers the Government first become aware of mephedrone last summer.
He said revellers at the Isle of Wight music festival had been found to be taking the drug, which has effects similar to ecstasy and amphetamine.
The minister said the drug, which is part of a group of substances known as cathinones, had been linked to a number of deaths in the UK.
He said the Advisory Council on the Misuse of Drugs (ACMD) wrote to Home Secretary Alan Johnson in September and then later in December, when it informed him there was "evidence of harm".
Mr Johnson then waited for the "full, proper advice" that arrived in March before deciding to ban the drug.
The ACMD has been rocked by a series of high profile resignations in recent months after the chief drugs adviser, Professor David Nutt, was sacked last October for publicly disagreeing with the Government's decision to reclassify cannabis.
Only last week, Eric Carlin became the latest ACMD expert to resign, claiming ministers had pledged to ban mephedrone to appear to be "acting tough" in the run-up to the election.
He said experts were being ignored and the council was "not doing its job".
Today Lord West told peers: "In terms of being a knee-jerk reaction, I don't think that is the case."
He added: "I think it was acting very properly and quickly as we needed to do."