Has cocaine use really doubled in five years?

“Cocaine use in Britain has more than doubled in five years, analysis of waste water reveals”

Telegraph, 18 May 2019

“Britain's cocaine crisis: Use doubles in last seven years as one in 50 Londoners snorts the class A drug on a daily basis and purity soars”

Mail Online, 19 May 2019

“Cocaine use doubles in Britain in five years and purity levels at record high”

Independent, 19 May 2019

There isn’t enough evidence available to say that cocaine use in Britain has doubled, and certainly not that one in 50 Londoners are snorting it.

These news stories do highlight something important, though. Cocaine use is almost certainly growing in certain cities and, thanks to new research into wastewater, we know much more about how much cocaine people are taking than we used to.

The reports are based on a European research study into drugs and wastewater. Scientists from major cities across Europe have been testing samples of wastewater from sewage plants, to measure how much of different substances are in people’s urine. They apply these findings to the population served by the sewage works, to come up with the average consumption of different substances per person.

For London and Bristol—the two UK cities in the study—they’ve found that concentrations of cocaine have been increasing for the past 5-7 years. In London, for example, they estimated just under 400mg per 1,000 people per day, in 2011. By 2016, that was up to nearly 900mg. That’s what the news reports mean by a “doubling” of cocaine use.

We don’t know enough detail about the methodology behind the claim that “one in 50 Londoners” are snorting cocaine to assess its accuracy.

So does this mean more people are using cocaine?

On the surface, it’s likely that this data reflects some increase in the number of people using cocaine on a daily basis in the cities concerned. But we need to be cautious about concluding that usage in these places or across Britain has “doubled” or that “one in 50 Londoners” are snorting cocaine.

First of all, these findings don’t tell us about the number of people using drugs, they just give us a sense of the total amount going into sewage.

Harry Sumnall, Professor in Substance Use at Liverpool John Moores University, told us:

“The technique is unable to provide estimates on prevalence and frequency of drug use, or provide insights into who is taking drugs, the purity of those drugs, or patterns of use – you still need surveys and other types of data to assist with this.

“The total amount of drugs used across a population is not uniformly distributed. Most people in a city will have never used an illicit drug, and amongst those who have, most of the total amount will be consumed by a smaller subset. Hence it’s not possible to infer that detection of a certain amount of drug in wastewater represents use by a specific proportion of people in the analysed area.”

Secondly, London and Bristol are not the whole of Britain. They’re two cities in the south of England, and we’ve no way of knowing how well their findings would reflect usage in towns or other cities or more rural parts of Britain. The European researchers make clear that drawing assumptions about an entire country from a limited number of plants and locations is unreliable.

It’s also not clear whether the findings cover the whole populations of the cities or just those served by the same sewage works.

The news articles reporting on this study mentioned the locations involved in the study, but this point didn’t make it into any of the headlines.

Other evidence does suggest the quantity and purity of cocaine have been rising in recent years. Seizures of cocaine by police and the Border Force rose in the years up to 2016/17, although that’s been followed by a fall in 2017/18. The National Crime Agency also reports that the purity levels of cocaine it is monitoring are at historically high levels.

Survey evidence suggests cocaine use is growing, but it has big limitations

The ‘traditional’ method of estimating how many people use cocaine is to ask people in a confidential survey. In England and Wales, the household-based Crime Survey fills that role.

The survey tells us that about 2-3% of adults aged 16-59 say they have used powdered cocaine in the past year, and that’s been broadly stable since the early 2000s. There’s been a slight uptick in the reported rate in the last year we have figures for—2017/18.

The picture is clearer among 16-24 year-olds specifically. In 2017/18, an estimated 6% reported using powdered cocaine, which has been on an upward trend in the last five years.

Very few people report using crack cocaine, by comparison.

There are also figures for London specifically—which actually broadly show falls in the proportion of people reporting cocaine use over the last five years.

But we can’t entirely rely on these figures. The obvious point is that people may not be completely honest about doing something illegal, even if the survey is confidential.

And there are also problems in who the survey is asking. As Professor Sumnall puts it:

“It’s a household survey and tends to underrepresent some groups of people more likely to use drugs, relies on people reporting behaviour they know is against the law, and with newer drugs, people often don’t know exactly what they’ve taken.”

We’re waiting to hear from the original authors of these claims

There’s only so much we can say at the moment about the claim that cocaine use has doubled. Several of the figures used in the reports seem to originate from disclosures to the Telegraph from a researcher at King’s College London (KCL), which is one of the universities involved in gathering data for the UK as part of the European study.

We contacted KCL to find out more about where these claims come from, and to ask for more information about their role in the study. We were told that no one was available to speak to this week. KCL also haven’t published any information on their study to back up the coverage in the Telegraph.

This is unsatisfactory. Claims like these which are published by a national newspaper should be checkable, and that means both that the original source should be made available and that there should be a contactable point person, especially in the days following a news splash. Neither was the case here.