The mephedrone scare started at the end of 2009 when newspapers and the BBC reported that Gabrielle Price, a 14-year-old girl from Brighton, had died after taking the drug. The story was based on rumour and police statements.

Just a month later, however, it became clear that she had died not from a mephedrone overdose but from an infection. The drug was not found in her system.

But the media storm did not abate and a few weeks later it happened again. Our friends in the police again blamed mephedrone for the deaths of two young men in the north-east, Louis Wainwright, 19, and Nicholas Smith, 18. Humberside police said: "We have information to suggest these deaths are linked to M-cat [a street name for mephedrone]."

Once again, this was before any toxicology tests had been performed.

The boys in blue were assisted in spreading the ensuing moral panic by the National Association of Head Teachers, whose general secretary Mick Brooks told the BBC: "'This drug clearly has the same inherent dangers as any Class A drug."

The NAHT repeated this on BBC Radio 4's Today programme, who did not deem it necessary to turn to a pharmacologist for a view on the matter, or question what toxicological expertise or test results the spokesman for head teachers was drawing upon.

Last month we learned that the two teenagers had not taken the drug after all.

Unfortunately the damage has already been done, because in the run-up to the general election the media whipped themselves into a frenzy over mephedrone, blaming it for the deaths of 18 teenagers in total.

The Home Office minister, determined to make the welfare of tabloid news editors his top priority, promptly promised tough action, pausing only to await formally the advice of the Advisory Council on the Misuse of Drugs, as he is bound to do under the Misuse of Drugs Act 1971.

You may recall that the ACMD had already lost most of its scientists who resigned in protest at the then home secretary Alan Johnson's unfair treatment of its former chair Professor David Nutt. Another member resigned the day the ACMD met to approve its report on mephedrone.

The meeting was rushed through so that the chairman could attend a press conference at which Johnson announced the report's recommendations and the government's response, before the meeting had even finished discussing the report.

In so doing the home secretary was in fact breaching the Principles for the Treatment of Scientific Advice, which the government reluctantly agreed with the science community following the storm of protest over the sacking of Nutt. The purpose of the principles was to prevent scientific advice being distorted for political ends.

In its report, the ACMD recommended a ban, more on the basis of mephedrone's chemical similarities to other banned drugs than anything else. On deaths, the ACMD noted that, while there had been 28 cases in the UK "where cathinones [the class of chemicals that includes mephedrone] have been implicated", there had not been a single case where mephedrone was shown to be the cause of death.

Indeed, it pointed out (page 20, paragraph 5.16) that:

The UK number of cases are subject to several caveats:

• Not all suspected cases may have been identified;

• That mephedrone may have been involved in a death cannot be confirmed until the relevant coroner or Procurator Fiscal has concluded her/his inquest or other formal inquiry; and,

• The presence of mephedrone in post mortem toxicology does not necessarily imply that it caused or contributed to a death.



Nevertheless, both media and politicians continued to claim that mephedrone was killing people, without any evidence to support the assertion. In the House of Commons debate on the Misuse of Drugs Act Order, which brought the ban into force, Alan Campbell, a minister in the Home Office, repeated the claim:

"Mephedrone has been linked with a number of deaths in the UK and one confirmed death of a young girl in Sweden."



Conservative MP William Cash asked:

"How on earth could anyone reasonably argue that mephedrone is not something that causes the death of young people and generates all the symptoms that he described?"



Keith Vaz, chair of the Home Affairs Select Committee, went even further arguing that young people should be told:

"'Take this drug and you will die', as 25 teenagers and young people have done since this matter was referred to my right honourable friend the member for Redditch."

He went on to claim:

"Those 25 young lives could have been saved if the Advisory Council on the Misuse of Drugs had produced its report more quickly following the minister's referral of the matter to the advisory council."



The Lib Dem policy is to take the advice of the ACMD on drug classification and we supported the classification decision, broadly on the same basis that the ACMD did – that mephedrone was chemically, and neuropharmacologically, an ecstasy-like drug.

I was not willing to let those wild allegations about its lethality go unchallenged, however, so I pointed out that the ACMD's report actually "makes it clear that we cannot say that the 25 deaths linked to the use of mephedrone were caused by mephedrone".

There has not been a single case in the UK where causation has been established. This is surprising given that if you ingest enough of any substance – no matter how legal – you can kill yourself. Even water.

Banning something does not stop people from doing it, but the effects of criminalisation are likely to make it less safe.

Drugs can certainly screw you up. But a criminal record for drug use is more likely to screw you up.

Decisions like this should be based on a balance of harms. The ban on this drug was implemented – and rushed through – partly on the basis that it was causing serious harm, that it had caused several deaths. This is not borne out by the evidence.

Furthermore, if it turns out that mephedrone was relatively less harmful than alternatives that mephedrone users might turn to (alcohol, contaminated mephedrone, other illegal drugs or the next generation of "legal highs") then the effect of the health panic over mephedrone would be to imperil more young people.

Great result Mr Johnson!

Another casualty of the mephedrone panic has been the ACMD, whose reputation has been damaged by its part in the rushed ban. Another member, Eric Carlin, resigned in protest.

The hysteria over mephedrone is a classic example of indulgent moral outrage at the expense of a common-sense harm reduction strategy. Banning something – or more accurately, imposing a criminal penalty on some action – has harms attached too.

If we want to reduce the harms posed by drugs, we need a more mature and considered public discourse, and we need to start with a solid evidence base.

It will be interesting to see when the next legal high comes along – as it surely has already – whether the media or politicians will pause to reflect on the role that banning a potentially less harmful alternative will have played in any deaths apparently caused by its replacement. Place your bets.

Evan Harris is a former Liberal Democrat MP and science spokesman