The central aim of prohibition is to reduce or eliminate illegal drug use and one of the central arguments against law reform is that it would lead to increased use. In this context prevalence of drug use is arguably the most politically important indicator for the effectiveness of current policy.
Simple descriptions of prevalence rising or falling mask a great deal of complexity within prevalence data. It can be broken down by drug, by age group, by sex, ethnicity, geography and so on. Data can refer to use in the last week, month, year or during a lifetime. Importantly, general prevalence data does not make a distinction between different patterns of use and crucially does not measure harm, associated with use (eg binging, poly drug use, un-safe behaviours like injecting, addiction).
The United Nations Office on Drugs and Crime 2008 World Drugs Report includes estimates for the extent of global drug use:
The source for this data is from UNODC Annual Reports Questionnaire data, National Reports, and UNODC estimates. The UNODC acknowledges that much of the data is severely limited and out of date. For this reason the UNODC figures should be treated with scepticism, as they are essentially a guess (often politically skewed) rather than the result of a scientifically rigorous survey.
The British Crime Survey (BCS) is a large national survey of adults who live in a representative cross-section of private households in England and Wales. In addition to asking respondents about their experiences of crime, the BCS also asks about a number of other crime-related topics. Since 1996, the BCS has included a comparable module of questions on illegal drug use. This examines the prevalence and trends of illegal drug use among 16 to 59 year-olds.
The 2006/07 British Crime Survey shows that the proportion of 16-59 year olds admitting to having used an illegal drug during the last year is at the lowest level since the survey began. This is largely due to a decrease in cannabis prevalence. Cannabis is by far the most commonly used illegal drug in the UK and therefore even very small percentage changes in its use will have a big affect on the total number of drug users.
Despite the fall in overall drug use, class A drug amongst 16-59 year olds in the last year has increase 2.7 per cent in 1997 to 3.4 per cent in 2006/07. This is largely due to a significant increase in cocaine prevalence.
↑↓ Statistically significant change 1998 to 2006/07
The BCS only surveys private households which could result in inaccurate results. The report notes that this "does not cover some small groups, potentially important given that they may have relatively high rates of drug use: notably the homeless, and those living in certain institutions such as prisons or student halls of residence. Nor, in practice, will any household survey necessarily reach those problematic drug users whose lives are so busy or chaotic that they are hardly ever at home. As a result, the BCS is likely to underestimate the overall use of drugs such as opiates and crack cocaine, where the majority of users are concentrated within small sub-sections of the population not covered by the survey." [p7].
Evidence of the British Crime Survey's in inaccuracy in measuring opiate and crack cocaine usage is perhaps demonstrated by an alternative estimate provided by an online Home Office report. Instead of asking people what drugs they have used, an estimate of the number of opiate, crack cocaine and injecting users was extrapolated from drug treatment, probation, police and prison data. The figures are over six times higher than those from the BCS covering the same period.
Like many drug usage surveys, the BCS does not include figures for two of the most popular drugs: alcohol and tobacco. The Office for Nation Statistics produces a General Household Survey (GHS), which includes statistics for alcohol and tobacco. Unfortunately it does not ask the same questions as the BCS but it can still provide some comparison for levels of legal drug use.
According the 2007 GHS 64% of the UK population (over 16 years old) used alcohol in the last week, 21% were regular smokers and 24% were ex-regular smokers. The GHS only includes households, which means it will be subject to the same problems as the BCS.
The Office of National Statistics 2002 report Tobacco, Alcohol and Drug use and Mental Health is another household survey which provides an incredibly detailed breakdown of prevalence data based on original survey research undertaken in 2000. It reported that 88% of the UK population (between 16-74 years old) had drunk alcohol in the last year, 11% had used an illegal drug in the last year and 30% were regular smokers. The report found large differences between age and sex, and illegal drug usage with young men being the group most likely to have use illegal drugs.
The Observer newspaper carried out a poll about people's attitudes to drugs in 2002 which found that 28% of the UK population over 16 have used an illegal drug. It also found big differences in usage between age and sex: men were twice as likely as women to have used an illegal drug (38 and 18 per cent respectively) and 51% of 16-24 year olds have used drugs.
The European Monitoring Centre for Drugs and Drug Addiction's (EMCDDA) Annual Report includes the results from drug usage surveys from many European countries. Not all the surveys use the same methodology so caution needs to be taken when comparing data from one country with another. Caution is also needed when assessing overall European trends as they will be heavily influenced by data provided by a few large countries.
According to EMCDDA 2005 Annual Report, the UK has the highest lifetime prevalence of drug use for cocaine, amphetamines, ecstasy and LSD, and is third after Denmark and France for cannabis (see caution above).
For prevalence of drug use in the last year, the UK is amongst the highest in Europe with the report noting that "analysis of school data and general population survey evidence suggests that, on most measures, the Czech Republic, Spain and France have now joined the United Kingdom to form a group of high-prevalence countries".