Underestimation of Drug Use: A Perennial Problem with Implications for Policy

by Olivia Maynard

Follow Olivia on Twitter

Photo by Louie Castro-Garcia on Unsplash

In a paper recently published in the journal Addiction, Hannah Charles and colleagues suggest that the prevalence of illicit drug use among 23-25 year olds in a Bristol-based birth cohort (ALSPAC) is over twice that reported in the Crime Survey for England and Wales (CSEW). The team propose that these figures reflect under-reporting in the CSEW, although they note that they may reflect higher levels of illicit drug use in Bristol. Here I present some preliminary data supporting their view that the CSEW underestimates illicit drug use.

In March 2020, I recruited 683 UK university students to participate in a short survey on drug use via the online survey platform Prolific which has been shown to produce reliable data. I recruited only students aged 18 to 24 years who reported using alcohol in the past 30 days, and participants reported whether they had used any of MDMA/ecstasy, cocaine or cannabis in the past two years.

Table 1. Prevalence of self-reported illicit drug use across three surveys of young people in the UK

via ProlificAged 18-24
Bristol, ALSPAC

Aged 23-25


Aged 23-25

2 years 1 year Lifetime 1 year Lifetime
Any illicit drug usea 52.7 (360) 36.7 62.8 16.4 40.6
Cannabis 50.2 (343) 29.2 60.5 13.8 37.3
MDMA/ecstasy/amphetaminesb 23.3 (159) 17.0 32.9 3.6 11.1
Cocaine 21.1 (144) 19.6 30.8 4.8 13.9

Notes: Values represent percentage of participants (number of participants). Percentages for CSEW and ALSPAC are taken from Charles et al (1) and are weighted percentages.
a ‘Any illicit drug use’ refers only to the illicit drugs assessed in the respective surveys (only cannabis, MDMA and cocaine in our survey), more drugs in ALSPAC and CSEW – see Charles et al (1).
Our Prolific survey asked about ‘MDMA / ecstasy’ use, ALSPAC categorised ecstasy/MDMA use along with other ‘amphetamine’ use and CSEW asked about ‘ecstasy’ use.

Over half of my sample reported using at least one of cannabis, cocaine or MDMA in the past two years (Table 1). This is markedly higher than the CSEW’s estimates of either past year or lifetime use, and more in line with those reported in ALSPAC. Comparing across drugs, past two-year use of the three drugs is higher in my survey than either past year or lifetime use in the CSEW, and higher than past year, but lower than lifetime use in ALSPAC. Perhaps of more interest than ever use of the drugs over the past two years, I also examined the combinations of drugs students in my survey were using (Table 2). I find that the majority of students who report using illicit drugs have only used cannabis in the past two years (25% of all students), although the second largest group (15%) have used all three of cannabis, MDMA and cocaine.

Table 2. Prevalence of self-reported illicit drug among UK university students

Qualtrics survey of university students (past two years)
Illicit drug use 
Cannabis 50.2 (343) 48.5 (163) 53.5 (167) 37.1 (13)
MDMA / ecstasy 23.3 (159) 19.3 (65) 29.2 (91) 8.6 (3)
Cocaine 21.1 (144) 17.6 (59) 26 (81) 11.4 (4)
Illicit drug use profiles
Alcohol only (no illicit drug use) 47.3 (323) 48.2 (162) 44.6 (139) 62.9 (22)
Any illicit drug usea 52.7 (360) 51.8 (174) 55.4 (173) 37.1 (13)
Cannabis only 24.5 (167) 27.4 (92) 21.5 (67) 22.9 (8)
Cannabis + Cocaine + MDMA 15.4 (105) 11.3 (38) 20.8 (65) 5.7 (2)
Cannabis + MDMA 6.3 (43) 6 (20) 7.1 (22) 2.9 (1)
Cannabis + Cocaine 4.1 (28) 3.9 (13) 4.2 (13) 5.7 (2)
Cocaine only 0.9 (6) 1.2 (4) 0.6 (2) 0 (0)
MDMA only 0.9 (6) 0.9 (3) 1 (3) 0 (0)
Cocaine + MDMA 0.7 (5) 1.2 (4) 0.3 (1) 0 (0)

Notes: Values represent percentage of participants (number of participants).
‘Illicit drug use’ refers to participants reporting any use of the three drugs in the past two years.
‘Illicit drug use profiles’ refers to the combinations of drugs participants report using in the past two years.
a ‘Any illicit drug use’ refers only to use of cannabis, MDMA and cocaine.

There are some important differences between my sample and both the CSEW and ALSPAC samples. Some differences may mean that my figures are overestimates, including sampling university students who are more affluent than the general population (although drug use is not necessarily higher among students than non-students) and only including those who reported drinking alcohol (although according to the study authors, over 95% of the ALSPAC participants report past year drinking). Other differences may mean my figures are underestimates, including only asking about use of three drugs (thereby underestimating ‘any illicit drug use’), and the younger average age of my sample. I also report on past two-year use, rather than either lifetime or past year use as per CSEW and ALSPAC. Given these differences, I would like to run a larger, more representative sample on the Prolific platform (Prolific allows researchers to recruit a sample which is representative of the general population), to get an estimate of illicit drug use which is more comparable to ALSPAC and CSEW.

Despite these differences, my data support those reported by Charles and colleagues. Indeed, I find it unsurprising that illicit drug use is under-reported in the Home Office’s CSEW. The validity of self-reports for sensitive issues has long been a concern. Over-reporting of illicit drug use is not considered to be a concern and numerous methods have been developed for preventing under-reporting (see a 1997 NIDA report on this issue, as well as more recent techniques for estimating prevalence of use such as the crosswise method). It is important to consider the context in which surveys are administered, including participants’ perception of who is asking the questions and for what reason. It seems that if drug use is asked about in a research context, (e.g., with a clear research objective, informed consent and no possibility of repercussions), the validity of responses may be higher than when questions are asked by organisations that are perceived to be involved in the punishment of people who use drugs (e.g., governments, universities).

While the CSEW recognises that it does not reliably measure problematic drug use, my data and that of Charles and colleagues provide evidence that CSEW’s claim that it is a ‘good measure of recreational drug use’ may be wrong. Although it may be convenient to believe that only a small subset of the population uses illicit drugs, accurate information may galvanise policy makers (both nationally and locally, including at universities) into developing drugs policies that reflect reality and which support, rather than criminalise, the large proportion of the population who choose to use drugs. Indeed, this is what we’re doing at the University of Bristol, where it has been accepted that drug use is relatively common among our students and we’re providing support and education to those students who need it.


This blog posted was originally posted on the Tobacco and Alcohol Research Group blog

Drinking in pregnancy: the right to record, or the right to privacy?

Luisa Zuccolo , MRC Integrative Epidemiology Unit and Department of Population Health Sciences, Bristol Medical School, University of Bristol

Cheryl McQuire, School for Public Health Research/Centre for Public Health and Department of Population Health Sciences, Bristol Medical School, University of Bristol

Follow Luisa and Cheryl on TwitterCheryl McQuireLuisa Zuccolo

What’s the issue?

Drinking alcohol during pregnancy continues to stir passionate and polarised reactions. The issue has once again come into sharp focus. In England, the National Institute for Health and Care Excellence (NICE) is proposing to measure all alcohol use in pregnancy and transfer this information to a child’s health records, without explicit agreement from the mother. The aim of the proposal is to ensure better diagnosis and support for those with lifelong conditions caused by drinking in pregnancy that can include problems with learning, behaviour and physical abnormalities, known as Fetal Alcohol Spectrum Disorders (FASDs). However, the NICE proposal has been met with strong opposition from some organisations, which say that this breaches pregnant women’s right to medical privacy.

A balancing act

Benefits of introducing the proposed FASD NICE Quality Standards

It’s important to remind ourselves why measuring and sharing information on drinking in pregnancy could be worthwhile, and who will benefit.

Information – the key to understanding

Official guidance recommends that it is safest not to drink at all during pregnancy, or when trying for a baby. But a quarter of people in the UK are not aware of this guidance and the UK has the fourth highest rate of drinking in pregnancy in the world. The new NICE quality standards propose to rectify this by making it compulsory for midwives (or other health care professionals) to have conversations about alcohol with pregnant women.  The idea is to help women to make informed choices about drinking in pregnancy.

Information is in everyone’s interest. We still don’t know enough about the effects of different levels of alcohol use in pregnancy. This is a tricky area to study, in large part because we don’t have enough information. If we don’t measure, we can’t fully understand the effects of alcohol in pregnancy (not even to confirm whether small amounts are safe). This has been our area of research for a number of years, and it is important both because many pregnant women drink alcohol, and because they should have the right to be better informed. Current abstinence guidelines are largely (but not solely) based on the precautionary principle. Our research has provided some evidence that even low levels of use (two drinks a week or fewer) can have negative effects, including smaller babies and preterm birth. We need more information to find out about the full extent of these risks – including whether the risks are genuinely there – to ensure that women can make informed decisions based on the best possible evidence.

Diagnosing fetal alcohol spectrum disorders (FASD)

Fetal alcohol spectrum disorders are severely underdiagnosed. They are characterised by lifelong problems with learning, behaviour and, in some cases, physical abnormalities. Contrary to what many think, these are common disorders. Our recent research suggests that between 6 and 17% of children in the UK could have symptoms consistent with FASD. Without good information on exposure to alcohol in pregnancy, many of these children remain ‘invisible’ to services and do not get the support that they need.

Pregnant woman holding a glass of red wine

Concerns about the Quality Standards

Despite the potential benefits of these proposals, there are several unresolved issues that need tackling urgently.

Stigma and trust

If women feel stigmatised, they might lie about their drinking, invalidating any data collection. If they can’t trust their healthcare providers, then we can’t trust the data – so what would be the point of collecting it?


What would women be offered, in exchange for volunteering this information? What’s in it for them? It would be unbalanced and probably unethical to request information about drinking in pregnancy, at the risk of stoking maternal anxiety, without explaining the reasons, or offering support if so desired. The treatment of pregnant women who smoke provides an appropriate model – information is recorded on antenatal notes, and support to quit is offered at the same time. We need to guarantee a non-judgmental and supportive approach to listening when it comes to alcohol too.


Women should be able to opt out. For those opting in, it should be made clear that the same high levels of confidentiality will apply as are already in place for current information from maternity notes and child health records. These new data on alcohol use should be no different and must be covered by existing guarantees.

Finding the right balance

So, where is the balance between the benefits and risks of the proposed changes? We often talk about burdening pregnant women with anxieties, but we neglect to talk about the lifelong consequences of emotional and behavioural problems arising from exposure to alcohol in pregnancy – these pose real everyday challenges for families, for many years to come. If on the one hand, maternal health is child health, then on the other child health is maternal health.

As we hear in these COVID-19 times, health is a marathon not a sprint

We need to continue shifting the focus from ‘healthy pregnancies’ to ‘healthy families’. The former can be met with resistance by those evoking the dangers of the surveillance state and policing women’s ‘baby-making’ bodies. The latter reminds us of the many individuals involved, all equally important, all of whom need support for the long term beyond those initial nine months.  We believe that NICE should listen to the plurality of women and families’ voices. The debate on recording alcohol in pregnancy will lead to constructive health gains that will benefit all.