The 2010/11 sweep of the British Crime Survey (BCS) was the first to ask over 27,000 respondents from representatively-sampled households about whether they had used mephedrone in the past year. Nearly 3,700 of the BCS respondents in 2010/11 were aged between 16 and 24.

But the interesting  question that the published BCS report did not answer was this: for each of the five sweeps from 2006/07 to 2010/11, what proportion of 16-24 year-olds  reported past-year  use of “cocaine powder and/or ecstasy and/or mephedrone”. Clearly, only the 2010/11 sweep asked explicitly about mephedrone but, if all three drugs share essentially the same market, then the answers have some direct relevance – as we show below.

I am grateful to Andrew Britton of the BCS team who kindly responded to my request for additional data on multi-drug usage from BCS to enable the above question to be answered, see Table.

On recent past performance from 2006/07 to 2009/10 (SS3), we’d have expected around 7.0 per cent of 16-24 year olds in 2010/11 to have reported past-year cocaine use. But only 4.4 per cent did. Using my estimated standard errors, the decrease was highly statistically significant compared to both of the two preceding pairs of BCS sweeps; and may have implications for cocaine-related deaths in 2009 and 2010.

From the new entries in the Table, we notice that only a minority of 16-24 year old past-year users of cocaine powder and/or ecstasy used ecstasy but not cocaine in the past year: 20 per cent (1.4/6.9) in 2006/07+2007/08;  15 per cent (1.1/7.3) in 2008/09+2009/10; and 25 per cent (1.45/5.85) in 2010/11.

More importantly, we observe that the 16-24 year old market for cocaine powder and/or ecstasy and/or mephedrone in 2010/11 was 7.6 per cent of the age-group (95 per cent CI:  6.6 - 8.7 per cent) when – for cocaine powder and/or ecstasy -  it had been essentially 7 per cent of the age-group for the preceding four sweeps of BCS. Thus, we see clearly that mephedrone does not appear to have greatly expanded the niche market, but seems rather to have shifted young people’s choice of drugs away from the most lethal in the trio – cocaine powder.

Indeed, from the Table, it transpires that 23 per cent of the 16-24 year old market (1.77/7.62) used mephedrone but neither cocaine powder nor ecstasy in the past year.The percentage is even lower, at around 10 per cent, for 25-59 year old users (0.19/1.96) of cocaine powder and/or ecstasy and/or mephedrone, see lower panel of Table. Since cocaine’s lethality is greater in the older users, they may have more to gain from switching away from cocaine use.

The back-story on mephedrone is as follows. Readers will recall that, on advice from the Advisory Council on the Misuse of Drugs (ACMD), legislation was passed on 16 April 2010 under UK’s Misuse of Drugs Act to control mephedrone as a class B substance.

The ACMD knew that soldiers’ cocaine (and ecstasy) positive rate in compulsory drugs testing was half the level in 2009 that it had been in 2008, and that the decrease was already evident in the last quarter of 2008, as I have reported before on this website. The ACMD also had information from Mixmag’s opt-in survey in late 2009 that mephedrone had achieved some notable market penetration by 2009 with two-thirds as many of Mixmag’s opt-ins using mephedrone as cocaine in the past month (also reported here).

The implication, also first suggested here, is that banning mephedrone may have done more harm than good, because its lethality was less than that of cocaine for which it had become a widespread and legal alternative.

Conflict of interest: SMB writes in a personal capacity but is a member of Home Office’s Surveys, Design and Statistics Subcommittee.