Monitoring drug use in the digital age: studies in web surveys

This set of papers aims to demonstrate the significant role that web surveys can play in drug data collection. Contributions from a diverse range of experts, who have conducted web surveys across local, national and international levels, show the breadth of such surveys currently in use in Europe and globally. In their own words, the authors show the role that web surveys can play in developing a deeper understanding of drug-related phenomena. The authors show how the findings and analyses from these surveys have supported policy-making and the development of novel online harm reduction tools and resources, underscoring the potential of web surveys in aiding responses to evolving drug issues.

Last updated: 9 December 2022

Papers in the collection

Currently available papers are shown below (more will be added as they become available).

1. Please note that due to the COVID-19 pandemic, the publication of these papers was delayed and that most of the papers were written before the pandemic.
2. The United Kingdom left the European Union as of 1 February 2020 some of the papers were drafted in the transitional period and might include information on the United Kingdom.


The EMCDDA would like to thank all authors, editors and reviewers who have worked on this publication. In particular, the insight benefited from overall editorial input by João Matias, Alexander Söderholm, Mike Vuolo and Nicola Singleton.

The EMCDDA gratefully acknowledges the reviewers drawn from the EMCDDA’s Scientific Committee: Catherine Comiskey, Gabriele Fischer and Margarida Gaspar de Matos. Furthermore, valuable review comments and input were received from EMCDDA staff members: Alessandra Bo, Alessandro Pirona, André Noor, Brendan Hughes, Eleni Kalamara, Federica Mathis, Jane Mounteney, Julián Vicente, Katerina Skarupova, Laurent Laniel, Paul Griffiths, Thomas Nefau, Tim Surmont. Peter Fay provided much appreciated help with editing the final publication.

What are web surveys and why are they important?

The online space has become increasingly relevant in identifying trends in illicit drug demand and supply. With increased internet activity globally, drug-related social interactions and purchases have also partially moved online. To respond to these developments, the EMCDDA has conducted extensive research on the intersection between the internet and drugs, such as the emergence of online drug markets and how new internet technologies have acted as facilitators of such markets (EMCDDA, 2016, 2020a). As drug-related activities have partially moved to online spaces, a range of online communities have become established where people who use drugs exchange their experiences. These developments have shifted the attention of researchers and monitoring institutions to the internet as a way to investigate activities related to the use, trafficking or production of drugs.

In particular, web surveys have become an important part of the range of tools used to understand drug-related phenomena, including assessing patterns of drug use and supply. Web surveys are self-administered electronic questionnaires that are accessible online.

While some surveys include both online and offline data collection, the focus of the papers in this report is on surveys solely run on the web for the purposes of collecting data on drug-related issues. As this collection of papers shows, web surveys have shown great promise in filling the gaps of pre-existing research on various issues in the drugs field. They have proved valuable in reaching large numbers of people who use drugs and in accessing some hard-to-reach groups of people in a quick and cost-efficient way, generating novel and detailed data about drug-related behaviours. While no single method can provide all information related to evolving drug phenomena, web surveys have provided an important point of triangulation when combined with other information sources.

This set of papers aims to demonstrate the significant role that web surveys can play in drug data collection. Contributions from a diverse range of experts, who have conducted web surveys across local, national and international levels, show the breadth of such surveys currently in use in Europe and globally. In their own words, the authors show the role that web surveys can play in developing a deeper understanding of drug-related phenomena. The authors show how the findings and analyses from these surveys have supported policy-making and the development of novel online harm reduction tools and resources, underscoring the potential of web surveys in aiding responses to evolving drug issues.

How do web surveys support drug data collection?

Web surveys enable drug data collection from a large sample of, most often, self-selected respondents. They can provide in-depth insights into the patterns, practices and features of drug use and drug markets, and the relationships between these variables (see contribution by Vendula Belackova and Eva Drapalova). These surveys are generally more cost-efficient than other data collection methods due to savings in participant recruitment, survey design and distribution, the time and cost of data transcription and the speed at which data can be processed. They also generally make it easy for respondents to decide when and where they want to complete the survey, placing the data collection tool at the convenience of the respondent.

The privacy and anonymity that are afforded by this approach have several added benefits. Among other things, the anonymity of online data collection on drug issues has been shown to help reduce response bias on sensitive topics such as drug use, as some studies have shown that respondents are more likely to report their substance use patterns through online surveys than, for example, self-administered paper surveys. The absence of an interviewer also seems to reduce the likelihood of respondents under-reporting socially undesirable and stigmatised behaviours, such as drug use. Taken together, the evidence indicates that web surveys are a robust tool for gathering information on potentially sensitive topics.

Web surveys have also shown promise in reaching hidden populations that may be missed by traditional sampling methods. This is seen in a number of the surveys included in this series of papers, which have reached large numbers of respondents via global, national and local samples and obtained rapid information on emerging trends in substance use.

Gathering data from hidden and other hard-to-reach populations has a clear benefit for decision-makers, enabling them to react to emerging drug trends. Web surveys have also become an additional tool for early warning systems to monitor the emergence of new or highly toxic substances on the drug market.

Overall, the many advantages offered by this approach enable web surveys to potentially fill crucial gaps in current knowledge about drug-related phenomena. These surveys can transcend national borders (e.g. the European Web Survey on Drugs and the Global Drug Survey), supporting cross-national cooperation in drug data collection and enabling the sharing of best practices to improve data collection techniques and respondent participation.

Limitations of web surveys

While web surveys have shown great promise, they are not without limitations. Importantly, since web surveys are generally based on self-selection and often have no pre-planned sampling frame (a list from which individuals are drawn for the sample), even with particularly large samples these surveys are usually not representative of the general population or of any pre-defined groups of people who use drugs. For this reason, web surveys cannot be used to develop general drug use prevalence estimates, and researchers need to exercise caution when interpreting results from such surveys. Nevertheless, two papers in this collection consider ways and methods in which web survey results may be generalised towards a larger population (see contributions by Stanislas Spilka et al. and Jonathan Caulkins et al.).

Moreover, due to the lack of a sampling frame, researchers must pay specific attention to where their sample has come from. The recruitment strategies they adopt, such as advertising on social media or specific internet forums or in-person at nightlife venues can play a large role in influencing the composition of their sample (see contribution by Jonathan Waldron and Meryem Grabski). Differences in internet use between and within countries also affect the composition of the sample, with internet use generally higher among younger people with higher education and socioeconomic status. However, as internet availability and access are increasing globally, and coupled with increasing smartphone use, web surveys will have the potential to reach much larger groups of people with increasingly similar attributes to the general population.

While web surveys can perform well in recruiting people who use drugs, sampling some groups of particularly hard-to-reach populations remains an issue. This includes, in particular, marginalised and vulnerable groups of people, for example, people who experience homelessness. It also includes those whose purchasing and social behaviours largely take place via the darknet, which is a small portion of the internet that has been intentionally hidden and is inaccessible through standard web browsers. This portion of the internet is widely known for illicit activities, such as drug purchases conducted on ‘cryptomarkets’, because of the anonymity it offers (EMCDDA, 2016, p. 135). Until now, most web surveys for drug data collection have been implemented on the openly accessible part of the internet, also known as the surface web. This points to the possibility that certain groups of people who use drugs are missed in these surveys. Nevertheless, and as shown in one of the papers, research is being undertaken on how web surveys can better reach individuals who are active on the darknet (see contribution by Julian Strizek and Alexandra Karden).

Web surveys could potentially be misused by respondents who may seek to manipulate their results. Therefore, careful data cleaning and checks on reliability and validity are a key step. The validity of the measures used within the surveys (that the questions used measure the intended phenomenon or fulfil the research needs) must be ascertained, both among items within a survey as well as through triangulating with other data sources (see contribution by Eleni Kalamara and Kateřina Škařupová). Carefully considered mechanisms are also needed to determine if a respondent fits the eligibility criteria of the survey (see for example contribution by Nadine Berndt and Rita Seixas) – as some respondents may, for example, fake their age in order to be able to complete the survey, due to age restrictions around informed consent.

Overall, while web surveys can be cost-efficient and rapid data collection tools, they do have some limitations. Being aware of these limitations and exercising caution when interpreting results are thus key considerations when web surveys are used for drug data collection.

The European Web Survey on Drugs (EWSD)

In 2016 the EMCDDA started a pilot project titled the European Web Survey on Drugs (EWSD), with the aim of developing a new system for collecting data on patterns of drug use in Europe (see contribution by João Matias). The main added value of the EWSD was to develop and test a web survey tool to collect and compare information on the frequency and amounts of drugs used, as well as on drug purchases, by different groups of people in several countries. This could in turn be used to help estimate the size of drug markets. The cooperative model adopted for the survey has proven highly successful, with the EMCDDA coordinating the study and participating countries being responsible for translating the questionnaire into their national languages and developing recruitment strategies. Through this approach, local country-by-country contexts and needs can be addressed, while maintaining considerable comparability across the participating countries.

Since 2016 the survey has expanded to include IPA7 (1) and EU4MD (2) countries, and in 2021 a total of 30 countries were involved in the survey. The EWSD has also been successfully adapted to gather data on emerging issues in the drugs field. In April 2020 a special round of the EWSD was launched in order to collect crucial information on the impact of COVID-19 on people who use drugs and on the services that support them.

Available in 21 languages, the survey gathered information on how patterns of drug use, access to health services and the drug market had changed in Europe during the first wave of the pandemic. The survey findings contributed to the emerging knowledge base on COVID-19 and Europe’s response to the pandemic, helping to protect the health of people who use drugs, improve drug services and raise awareness of market changes. The findings also informed an EMCDDA trendspotter report on the impact of COVID-19 on patterns of drug use and drug-related harms in Europe (EMCDDA, 2020b).

The EWSD has enabled the EMCDDA, the Reitox focal points (3) and other national partners to obtain valuable information on drug-related phenomena quickly and at a low cost. The triangulation of the data collected from the EWSD with other sources, such as general population surveys and drug price data collected by law enforcement, will continue to improve the understanding of different drug market dynamics and support policy development. Several of the papers in this collection present novel analysis and findings based on EWSD data, including discussions of the methodological aspects of the survey, underscoring the depth of data that the EWSD is able to collect from a large sample of respondents (see for example contributions by Jon Waldron and Meryem Grabski, Mike Vuolo and João Matias and Lies Gremeaux).

What other international web surveys support drug data collection?

As this report shows, there are now a vast number of web surveys that capture complementary data on drug-related phenomena. Some of these are linked to public health agencies or other national institutions, while others are run privately or by nonprofit organisations.

The Global Drug Survey (GDS) (see contribution by Adam Winstock et al.) is a major international web survey on drugs, run by a private research organisation with over 900 000 accumulated respondents to date. The data collected from this survey have been used to create several online harm reduction resources for people who use drugs and informed policy debates on drug use and its health and social consequences. Other surveys have extended their scope beyond people who use drugs to provide timely data on a range of aspects in drug markets. One such survey is the International Cannabis Cultivation Questionnaire (ICCQ), which was launched to facilitate international comparisons of small-scale cannabis cultivation (see contribution by Tom Decorte and Gary R. Potter). The survey has generated substantive findings about cannabis cultivation across several countries, especially among small-scale growers.

National web surveys have also been tailored to focus on new and emerging drug market developments. For example, in a context of increasing availability and declining prices of methamphetamine, the New Zealand Drug Trends Survey (NZDTS) was deployed to collect data on methamphetamine markets (see contribution by Chris Wilkins, Marta Rychert and Jose S. Romeo). The data from this survey has been central in understanding price differences between regions, including the sources from which people who use drugs acquire methamphetamine. Further, the Party Panel web survey tool was used in the Netherlands in response to the high variability in the amount of MDMA in ecstasy tablets found in the country (see contribution by Ygram Peters and Judith Noijen). By doing such, the Party Panel contributed to developing evidence-based interventions to reduce the harms associated with high-dose MDMA use.

Overall, the spread of web surveys internationally, and the diverse populations and topics they involve, highlight the considerable scope of issues they can cover in drug data collection and the resources and policies they can help develop to mitigate health and social harms.

Overview of papers in this collection

Three papers in this collection discuss the overall advantages and limitations of web surveys. Based on the lessons learned from pre-existing surveys, the papers outline key issues that researchers and decision-makers should consider when designing, implementing and analysing the results of web surveys. Vendula Belackova and Eva Drapalova set the stage by taking an in-depth look at the advantages, limitations and potential future of web surveys for collecting data on drug-related issues. As they show, a key limitation of web surveys is the lack of a sampling frame. As such, the results of web surveys cannot readily be generalised to any larger population. However, developments in the use of online methods have raised the possibility of moving towards representative online surveys, although none of these methods are without limitations. Nevertheless, web-based surveys offer a number of advantages, including increased speed and cost-efficiency of data collection, ease of collection using computer-assisted technologies, the ability to compare different groups in the data collected and, importantly, access to a large sample of people who use drugs.

João Matias introduces the European Web Survey on Drugs (EWSD), discussing its development from a pilot project to a survey implemented in over 30 countries and the lessons learned from the project. As the author highlights, the EWSD was developed in response to a need for more information on the size of the drug market in Europe, particularly by generating more in-depth data on the quantities of substances used by different groups of people who use drugs. Since then, it has been successfully used to improve European drug market estimates and identify emerging trends in the drugs field, for example in the context of the COVID-19 pandemic.

Eleni Kalamara and Kateřina Škařupová explore data quality in the EWSD using both quantitative and qualitative approaches, highlighting how such assessments can be a valuable component in improving the design and format of web surveys. The quantitative analysis examines participants’ engagement, respondent fatigue and the impact of item format. The qualitative analysis uses cognitive interviewing to examine the comprehensibility of the EWSD questionnaire among a focus group of Czech respondents. By doing such, it explores how country-level practices associated with drug acquisition and consumption can impact the accuracy and reliability of answers provided in the survey.

The subsequent three papers describe the challenges and opportunities of designing and implementing a tool for data collection on the internet. Alexandra Karden and Julian Strizek consider two different ways in which web surveys might be used to provide insights about people who purchase drugs on cryptomarkets on the darknet. First, the authors analyse EWSD data with respect to differences between people who reported buying drugs on cryptomarkets and those who obtained drugs from other sources. They then examine the challenges and opportunities related to sampling respondents through the darknet. The authors argue that while web surveys have considerable potential in generating large samples of people who purchase drugs on the darknet, it is important to improve the understanding of different recruitment methods for reaching diverse groups of people who use drugs.

Nadine Berndt and Rita Seixas discuss the challenges and opportunities of implementing the EWSD in Luxembourg. By comparing results from the country’s general population survey with the EWSD, the authors show how the EWSD presents an opportunity to complement existing data and gain deeper insights into patterns of drug use. The paper also discusses the importance of linking with national partners for successful survey implementation and how social media platforms were highly effective in recruiting participants. Lastly, the authors reflect on the methodological challenges and lessons learned from implementing the EWSD.

Jon Waldron and Meryem Grabski describe the development and design of the Electronic Music Scene Survey (EMSS). This online longitudinal survey sought to gain insights into patterns of drug use and nightlife participation among young adults. The paper highlights the importance of involving focus groups to ensure the relevance and acceptability of the survey content to the target population. It also shows how employing both an online and an offline recruitment strategy can help to determine whether the online sample is representative of the target population. The authors identify a number of lessons for future research practice, such as the importance of consulting with nightlife experts and involving focus groups in survey development.

Two papers describe the potential methodological steps that can be taken to make web surveys generalisable to larger populations. Stanislas Spilka, Stéphane Legleye and François Beck explore the potential of matching techniques, using data from the French general population survey and the EWSD. Known as propensity score matching or direct matching, this technique requires that the questions asked in the general population survey and the web survey are similar enough to ensure comparability on variables such as socio-demographics and frequency of drug use. Overall, the authors show how such techniques may enable researchers to generalise the findings from web surveys.

Jonathan P. Caulkins et al. explore raking and regression techniques to bring together the complementary strengths of general population surveys and web surveys to better estimate the size of drug markets. The authors do such by drawing together general population survey data with EWSD data from five different countries, with a focus on estimating the size of these countries’ cannabis markets. Raking re-weights responses to a web survey in an attempt to make the weighted averages or totals match those of the general population. Regression is used to impute values for what GPS respondents might have said if they had been asked about frequency of use and quantity consumed. The authors apply these two methods while examining their strengths and limitations.

Three papers demonstrate the analytical insights that have been drawn from the EWSD. Mike Vuolo and João Matias examine the four different sources from which the most commonly used forms of cannabis, herbal and resin, are acquired. Second, it analyses the relationship between sources of acquisition and frequency of use for these two forms of cannabis. The results of the analysis show that acquiring cannabis from a dealer and growing one’s own supply (and to a lesser extent purchasing it online) increases with frequency of use. While this pattern was highly consistent across countries for herbal cannabis, there was some variation for resin. These results highlight the importance of studying different forms of cannabis separately. As differences still exist between countries, context-specific issues may influence the relationship between patterns of use and sources of acquisition, which require further research.

Lies Gremeaux examines the different forms of MDMA consumed by EWSD respondents, studying intensity of use and patterns of buying behaviours with specific attention given to comparing the use of MDMA in tablet form and in the form of powder/crystals. The results show that both powder and crystalline forms are commonly used, indicating that these forms of MDMA have become well-established on the European drug market. The author shows that unlike most general population surveys, the EWSD reached a large sample of MDMA users and was able to further breakdown and study specific patterns of use. The author concludes that this type of information can enhance understanding of trends and developments in substance use in addition to emerging health threats. Such an understanding can be used to develop effective and tailored prevention and harm reduction interventions.

The following four papers present the analytical and policy insights drawn from other international web surveys. These papers demonstrate the diversity of web surveys for drug data collection globally and their influence in the development of novel online health and harm reduction interventions, as well as policies at the national level. Adam Winstock et al. from the Global Drug Survey (GDS), a large-scale international web survey with over 900 000 respondents to date, show how findings from web surveys can be used to develop web-based harm reduction resources. The authors examine the history of the GDS and the range of harm reduction tools that have been created using data from the survey, highlighting the importance of disseminating peer expertise to inform positive behaviour change. By doing such, the paper shows how web surveys for drug data collection can be used to help answer questions related to the epidemiology of psychoactive substance use and inform the development of novel harm reduction resources.

Tom Decorte and Gary Potter describe the International Cannabis Cultivation Questionnaire (ICCQ). This web survey specifically targets cannabis growers across 11 countries, with the authors showing how large-scale online surveys can be successful in reaching hidden populations of drug-supply involved individuals. The authors present some of the key findings from the first wave of the ICCQ and the methodological lessons learned from the survey. The paper explores the characteristics of cannabis growers across the included countries, such as methods of cultivation, motivations for growing cannabis, drug use and criminal justice contact. In a series of analyses, the authors also examine comparisons of recreational and medical growers.

Chris Wilkins, Marta Rychert and Jose Romeo examine results from the New Zealand Drug Trends Survey (NZDTS). This web survey was designed to provide timely local data on a range of aspects of the drug problem in New Zealand. Faced with increasing availability and declining prices of methamphetamine, in 2017 the NZDTS was adapted to collect data on the methamphetamine market in the country, focusing on the ease of acquiring the drug, prices and types of sellers. Drawing participants from across the country, the survey found that regions with higher levels of methamphetamine availability also reported significantly lower prices, and that respondents from rural regions with high methamphetamine availability and low prices were more likely to report buying this substance from a gang member.

Gjalt-Jorn Ygram Peters and Judith Noijen describe the web survey named Party Panel, which has been used in the Netherlands to provide insights into the subdeterminants of substance-use-related behaviours to develop theory- and evidence-based prevention initiatives. The paper focuses on the Party Panel round that was implemented in response to the high variability in the amount of MDMA in ecstasy tablets found in the country, contributing to developing evidence-based interventions to reduce the harms associated with high-dose MDMA use. As such, the authors show how web surveys can support prevention professionals to rapidly identify the behavioural subdeterminants to be targeted in campaigns responding to emerging risks.

The future of web surveys for drug data collection

This report is the first step in bringing together a comprehensive review of the advantages and methodological limitations of web surveys for drug data collection. It includes an overview of the range of such surveys implemented in this field and the novel health and policy responses they have helped inform. The potential of these tools is starting to be seen, particularly in terms of estimating the size of drug markets and studying emerging health threats. These examples highlight the future potential of web surveys in supporting policy-making and research.

As web surveys become more established, they also present opportunities to engage with a growing panel of respondents and ask them specific questions on emerging trends. This will further aid the understanding of and responses to emerging health and social harms. The 2020 special round of the EWSD on the COVID-19 pandemic is a case in point, as are the other examples presented in this report. In the future, web surveys could also allow direct interaction with other stakeholders and organisations working in the drugs field. This will support practitioners and decision-makers in better targeting their resources and policies to reach those most in need.

The potentials in this field are numerous. This report presents some of the successes of web surveys for drug data collection. In doing so, it also provides ideas for future research and analysis in this rapidly evolving area.

EMCDDA project group: João Matias, Alexander Soderholm, Katerina Skarupova, André Noor and Jane Mounteney.


EMCDDA (2016), The internet and drug markets, EMCDDA Insights 21, Publications Office of the European Union, Luxembourg.

EMCDDA (2020a), COVID-19 and drugs: drug supply via darknet markets, Lisbon, European Monitoring Centre for Drugs and Drug Addiction, Lisbon.

EMCDDA (2020b), Impact of COVID-19 on drug services and help-seeking in Europe, Trendspotter briefing, European Monitoring Centre for Drugs and Drug Addiction, Lisbon.


(1) These are the candidate and potential candidate countries for accession to the EU, which the EMCDDA offer ongoing technical support to familiarise the candidates with EU policies and working methods for participating in the work of the EMCDDA.

(2) EU4Monitoring Drugs (EU4MD) is the name of an EU-funded project developed and managed by the EMCDDA as part of its ongoing commitment to strengthening cooperation and sharing expertise. It involves countries in the European Neighbourhood Policy (ENP) area and will support national and regional readiness to identify and respond to drug-related security and health threats.

(3) Reitox is the European information network on drugs and drug addiction created at the same time as the EMCDDA. Members of the Reitox network are designated national institutions or agencies responsible for data collection and reporting on drugs and drug addiction.