Introduction

Narcotics-related activities can be defined and categorized very broadly either based on the different activities—misusing, possessing, distributing and positive urine drug test, or based on the amount of possession in grams, or the types of substance. The narcotics may be classified based on drug scheduling; an initiative developed by the United States Drug Enforcement Administration. In this schedule, drugs are categorized based on the potential level for misuse as well as medical usage – Schedule I (highest potential for misuse and has no medical use) to Schedule V (least potential for misuse and has medical use) (United States Drug Enforcement Administration). Hence, the crimes associated to different types of narcotics may be categorized into different classes and judged accordingly in a criminal proceeding.

Activities such as misusing, possessing, distributing and positive urine drug test are usually concentrated to particular regions or areas that in turn allows for anti-narcotics operations to be focused on those specific areas. Despite being endemic to specific hotspots, narcotics-related crimes are a global issue that transcend national boundaries. Moreover, knowing the time when substance misuse activities happen can further help authorities to conduct any anti-narcotics operations effectively. Due to this nature, spatiotemporal data of narcotics activities can be used to develop hotspots of the substance misuse crime and allow for mapping of substance crimes to be carried out.

This study is driven towards Sustainable Development Goals (SDG) Target 3: Good Health and Wellbeing, specifically Target 3.5 which aims to “Strengthen the prevention and treatment of substance misuse, including narcotic drug misuse and harmful use of alcohol”; which was first drafted by the Open Working Group (OWG) (UN OWG, 2014). Besides SDG Target 3, this work is also directed towards SDG Target 16: Peace, Justice and Strong Institutions. The SDG Target 16 section of a recent special edition SDG 2023 report has revealed that drug-trafficking is one of the major sources of illicit financial flow and Mexican drug cartels are estimated to have generated over $12.1 billion between 2015 and 2018 (UN, 2023). Therefore, identifying the hotspots of substance misuse hopefully will help in the prevention in short term and long term.

The United Nations Office on Drugs and Crime (UNODC) and the World Health Organization (WHO) have played major roles in delivering statistics and information to public regarding substance misuse and their associated virus infections. Considering that drugs misuse is commonly related to infections by the Human Immunodeficiency Virus (HIV) (UNODC, n.d; WHO, n.d), there is a plethora of documents published that integrates the two subject matters with spatiotemporal techniques (Aridoss et al., 2022; Brouwer et al., 2012; Campo et al., 2020; Ciccarone and Bourgois, 2003; Clipman, Mehta, Rodgers, et al., 2021; Clipman, Mehta, Srikrishnan, et al., 2021; Cooper et al., 2011; Des Jarlais et al., 2018; Des Jarlais et al., 2019; Hope et al., 2011; Jiang et al., 2019; Joshua et al., 2012; Kruse et al., 2009; Latkin et al., 1998; Martinez et al., 2014; Medhi et al., 2011; Nelson, 2020; Onovo et al., 2021; Rachlis et al., 2010; Roca et al., 1995; Scheibe et al., 2017; Tobin et al., 2012; Tobin et al., 2014; Williams et al., 2005; Wise et al., 2023; Xing et al., 2014; Xiong et al., 2010).

Besides HIV, the spatial relationship between drugs misuse and Hepatitis viruses (HBV and HCV) are often studied as well (Campo et al., 2020; Clipman, Mehta, Rodgers, et al., 2021; Clipman, Mehta, Srikrishnan, et al., 2021; Des Jarlais et al., 2018; Des Jarlais et al., 2019; Harris et al., 2012; Stopka et al., 2022). Another specific focus in the available literature is the misuse of drugs and sexual exchanges in general (Tobin et al., 2012), including those involving men who have sex with other men (Kunzweiler et al., 2018; Onovo et al., 2021; Tobin et al., 2014). In addition to the co-occurrence of drug misuse with diseases such as HIV and hepatitis that are a direct result of sharing contaminated needles, past research have also focused on drugs misuse and the resulting poisoning and/or overdose cases (Barboza et al., 2022; Bozorgi et al., 2021; Campo et al., 2020; Davlasheridze and Goetz, 2021; Des Jarlais et al., 2019; Hu et al., 2022; Liu et al., 2023; Marotta et al., 2019; Ransome et al., 2020; Ray et al., 2023; Rooney et al., 2018; Rostami et al., 2023; Sauer et al., 2021; Stopka et al., 2023). Some research have also studied on the content of drugs in wastewater and mapped them accordingly (Baker and Kasprzyk-Hordern, 2013; Castiglioni et al., 2015; Lai et al., 2016; Vazquez-Roig et al., 2012).

Previously conducted bibliometric analyses on narcotics-related activities or substance misuse are either country-focused (Bramness et al., 2013; Laaboudi et al., 2024; Sweileh et al., 2014) or time-bound (Bramness et al., 2013; González-Alcaide et al., 2016; Laaboudi et al., 2024). Sweileh et al. (2014) have focused on Arab countries and it was found that American researchers collaborated successfully with Arabian researchers. However, the use of spatiotemporal techniques is not a focus matter. On the other hand, Bramness et al. (2013) focused on the European and USA research related to substance misuse but limited to the research from 2001 and above. Similar to Sweileh et al. (2014), Bramness et al. (2013) barely focused on the use of spatiotemporal techniques in developing hotspots for activities related to substance misuse. Along with these two documents, the work by González-Alcaide et al. (2016) is also time-bound and does not consider the usage of spatiotemporal techniques in identifying hotspots of drugs-related activities. One of the latest scoping review documents has integrated the geographic information science (GISc) with the United States opioid overdose catastrophe (Sauer and Stewart, 2023). Sauer and Stewart (2023) have encouraged to explore the use of GISc involving illicit fentanyl as well to further delve deeper into sub-county by incorporating machine learning techniques as well. Our paper incorporates spatiotemporal techniques and narcotics-related activities keywords without erecting a barrier on country, continent and time frame, which in return, allows for comprehensive bibliometric analysis.

This article reviews a specific collection of pertinent documents published in Scopus, one of the largest available databases of scholarly works, and carried out spatiotemporal analysis. Using this collection of research documents, the importance and the advantages of using spatiotemporal techniques in mapping substance misuse activities can be identified. Besides that, this work may help the researchers to identify potential collaborators as well as publication outlets for their research documents related to the chosen topic.

Data acquisition and analysis methods

The Scopus database is recognized for controlling the quality of its journals via a vetting process that take several years and as a consequent of that process, the quality of articles is also subjectively of high quality. There are four phases of data extraction for the bibliometric analysis. In the Retrieval phase, phrases that are synonymous or associated with “space-time” as well as phrases synonymous with and related to “narcotic*” such as “drug*”, “addict*” and “misuse*”, are considered in the TITLE field of a search. For comprehensive search, names of narcotics such as ecstasy, stimulants, marijuana and others are added on the search query. Adding asterisk (*) symbol allows the search for longer words. For example, spatio* can be spatiotemporal or spatio-temporal and hotspot* can be either hotspot or hotspots.

The next phase, the Screening I phase, filtered out erratum and retracted documents. In the following Screening II phase, the documents are limited to those published in social sciences, mathematics, environmental, multidisciplinary, decision science, arts and humanities, psychology and economics only. The remaining documents then were manually filtered by reading the title and abstract of each document in order to remove documents that had little to no relation to the focus of our study in Screening III phase. The documents that remained at the end of the Screening III phase were used for the bibliometric analysis.

The Biblioshiny app developed by Aria and Cuccurullo (2017a) was utilized to conduct all the bibliometric analysis presented here. Further information on the R codes used for the bibliometric analysis can be referred to the work of Aria and Cuccurullo (2017b). The following research questions (RQ) and methods as presented in Table 1.

Table 1 Research questions (RQ) and associated methods.
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Results and Discussions

RQ 1 – Descriptive summary and distributions of documents

Table 2 shows the framework of the data extraction from Scopus database. A total of 45,926 documents were identified and had been published as of October 3rd, 2024, as retrieved by key words and key phrases-based search. The synonyms for the selected keywords have also been used to obtain a comprehensive set of research documents. A total of 393 documents were identified as erratum and retracted documents and were removed from the list leaving a total of 45,533 documents. Limiting documents to pertinent disciplines resulted in 17,650 documents. Manual filtering by reading the title and abstract of each document and this resulted in the removal of a further 17,327 documents that had little to no relation to the focus of our study. This resulted in a remaining 323 documents that were used for the bibliometric analysis.

Table 2 Field code and query for data retrieval.
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The 323 documents were authored by 1182 authors and published in 205 sources (Table 3). From these 323 documents, a total of 56 documents were published by single authors. Each document received an average of 18 to 19 citations. The number of documents published showed an annual growth rate of 6.28% indicating the importance and popularity in investigating narcotics-related activities using spatiotemporal techniques. The annual growth rate can also be seen as well in Fig. 1 which presents the annual scientific production of documents starting from 1974. All documents published and available in the Scopus database until October 3rd, 2024, were included.

Table 3 Summary of bibliometric analysis.
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Fig. 1
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Line graph of annual scientific production related to the spatiotemporal analysis of narcotics-related activities.

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The distributions of the documents published related to the spatiotemporal analysis of narcotics-related activities by type, language and frequency of authors are respectively presented in Tables 4–6. From Table 4, the 323 documents comprised majorly with research articles, followed by conference papers, book chapters, reviews, books and editorial notes. From Table 5, the 323 documents were mostly written in English and followed by Chinese, Spanish, French, German, Portuguese, Russian and Dutch. From Table 6, most authors only managed to publish one document. This may not be what is generally hoped for the development and future direction of the chosen topic. However, seeing five authors who are actively involved in the chosen topic, by publishing at least five documents, alludes to their sustained long-term interest and research focus in the subject matter (more on this in “RQ 2 – Authors’ productivity” and Table 7). However, it is important to note other possibilities for why some researchers were unable to publish more in this area. The main possibility could be the implementation of drug scheduling—Schedule I (highest potential of misuse) until Schedule V (least potential for misuse). For an example, Nutt et al. (2013) have studied the effects of Schedule I drug law on neuroscience research and treatment innovation. Despite having vast opportunity for certain drugs for medical use, a simple relocation of drugs from Schedule I to Schedule II is a complex and challenging task as it requires approval from multiple diplomats which include United Nations Member States (Nutt et al., 2013). Lebrero-Tatay et al. (2022) has summarized the main hurdles for the researchers prior to working on or about the drugs – requirement of special license, drug administration from licensed institutions, scarcity and costliness of the substances, as well as unsteady funding from private sources due to the social stigma. These may be the reasons why some researchers did not continue doing their research on narcotics crimes.

Table 4 Number of documents by type.
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Table 5 Number of documents by language.
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Table 6 Number of authors and documents.
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Table 7 Top 5 most relevant authors.
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RQ 2 – Authors’ productivity

From the 1182 authors that contributed the 323 documents, a list of top contributors to the research area on mapping hotspots for narcotics-related activities using spatiotemporal techniques revealed that Dansereau published a total of 6 documents, followed by Cheung, Cooper, Grunewald and Ross with 5 documents each. (refer Table 7). These authors can be described as active and productive in publishing documents related to the spatiotemporal analysis of narcotics-related activities.

Dansereau has published both the highest number of documents as well as the highest number of fractionalized documents. High fractionalized number of documents translates to producing research documents with few authors (Tajuddin and Ismail, 2024) and if the documents is highly cited, then the responsible authors have produced impactful documents throughout the lifespan of the documents. Luong (2023) has shown similar information regarding researchers who have produced impactful research documents on the darknet-related criminals separately using most relevant authors and most local cited authors. Bui et al. (2021) has also presented similar information for corruption research in ASEAN. In this study, Dansereau has the highest fractionalized number of documents with over 150 citations in total, which suggests that Dansereau has produced impactful research materials with a smaller number of co-authors, hence can be ranked as the most active and productive authors within this focus area.

The authors’ productivity was also investigated via Lotka’s Law (Lotka, 1926). Generally, as time goes by, more articles will be published and the number of authors that publish many documents will decrease in an exponential fashion. For the chosen topic, the authors’ productivity is presented in Fig. 2 and from this figure, authors who had published at least two documents on mapping hotspots for narcotics-related activities using spatiotemporal techniques can be categorized as “core” authors, which translates to the aggregate productivity of the authors. This can be seen from Fig. 2 when the theoretical distribution due to Lotka’s law (dotted line) is above the solid line for the 323 documents. These “core” authors can also be classified as active in producing research documents related to the use of spatiotemporal technique in mapping narcotics-related activities.

Fig. 2
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Authors’ productivity via Lotka’s Law - the dotted line is the theoretical distribution of Lotka’s Law whereas the solid line is the distribution of the 323 documents.

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RQ 3 – Top relevant and core sources of publications

On average, one source publishes 1.58 documents (based on the ratio of 323 documents to 205 sources) but in reality, some sources published more than 1.58 documents, and these sources may be considered as the top sources in publishing documents related to spatiotemporal analysis of narcotics-related activities. These top sources were investigated via the number of documents published as well as via Bradford’s Law.

Analysis on the number of documents published by top sources in descending order (Fig. 3) revealed that Substance Use and Misuse published a total of 9 documents, followed by Geography and Drug Addiction, Health and Place, International Journal of Drug Policy and Science of the Total Environment with 8 documents. Next, Journal of Urban Health as well as Plos One have published 7 documents, followed by Drug and Alcohol Dependence, International Journal of Environmental Research and Public Health as well as Journal of Substance Abuse Treatment with 5 documents each.

Fig. 3
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The number of documents published by top sources in descending order.

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Secondly, we identified core sources using Bradford’s Law, which generalizes that the sources of publications can be categorized into three classes with \(1:n:{n}^{2}\) ratios where the first category of sources are the “core” sources (Fig. 4). Through Bradford’s Law, an additional 10 sources which are Spatial and Spatio-Temporal Epidemiology, AIDS and Behavior, American Journal of Drug and Alcohol Abuse, BMC Public Health, Drugs and Alcohol Today, Social Science and Medicine, Addictive Behaviors, American Journal of Public Health, Applied Geography, Drug and Alcohol Review are also considered as “core” sources along with the 10 sources (from Fig. 3).

Fig. 4
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Core sources of publications via Bradford’s Law.

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RQ 4 – Top cited documents

The top cited documents on spatiotemporal analysis of narcotics-related activities are presented in Table 8. Despite the earliest document considered in this study dating back to 1974 by Chilton and Dussich (1974), eight out of the ten top cited documents were published in the 21st century. The top ten cited research documents in Scopus database were also searched in the Web of Science and Google Scholar databases, and the citations counts for these 10 documents are extracted from both databases.

Table 8 Top 10 most cited documents.
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The list of top ten cited documents was topped by Mattson et al. (2021) with 691 in the Scopus database, 707 in the Web of Science (WoS) database and 1011 in the Google Scholar (GS) database. The article by Mattson et al. (2021) reported on the trends and the geographic patterns of deaths due to drugs and synthetic opioids.

RQ 5 – Contribution by and collaboration among countries

Besides looking into the authors, their affiliations, and the platforms they publish in, the contribution of each country was also investigated in detail. Table 9 shows the total citations and average citations per article for the top 10 countries that are presented in a descending order. For total citations, the USA dominated with a total of 1976 Scopus citations, followed by the United Kingdom and Australia. However, looking into a more impact type metric using average citations per article revealed that the United Kingdom published articles that were generally cited 32.2 times, followed by France and Australia. Interestingly, China, India and Iran were also listed in the top 10 countries for total citations, but these three countries were not listed in the top 10 countries for average citations, which suggests that these three countries published many articles but received less citations. On the contrary, although Turkey was not listed in the top 10 countries for total citations, their presence in the top 10 countries for average citations suggests that researchers affiliated to Turkey published a smaller number of articles that had gained more citations.

Table 9 Top 10 counties’ involvement.
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In addition to total and average citations, it is important to investigate how the authors collaborate with other authors from different countries. This is majorly due to the fact that narcotics crimes are a global concern that spans across countries. Therefore, it is entirely justifiable for researchers from various institutions and countries to join forces and pull resources in addressing this issue. Figure 5 serves to illustrate the collaboration between countries, and the thinner lines report that a smaller number of collaborative works between two countries have been done, and vice versa. From Fig. 5, it can be clearly distinguished that the lines connecting the USA with some countries are thicker thus denoting a higher number of collaborative works that had been done by two or more institutions between the linked countries. It is not uncommon for USA to dominate the collaborative works with other countries, especially for the study related to crime prediction using artificial intelligence (Kaur and Saini, 2024), darknet-related criminals (Luong, 2023), cybercrime (Ho and Luong, 2022) and other fields, as seen from the thickness of the collaboration links from the respective studies.

Fig. 5
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Countries collaboration map.

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RQ 6 – Distribution of focused targets and place of study

Besides looking at the international collaboration, analyzing the targets of the research could also be done using heatmaps that are produced based on the frequency of the research target countries. SDG Targets 3 and 16 generally promotes better health and safer communities. By knowing the targets of the research, it is possible to identify which countries need to conduct research on spatiotemporal analysis of narcotics crime. We have excluded from the heatmaps studies that investigated all United Nations countries and European countries because such data could not be practically integrated into the heatmaps from studies for individual target countries.

Figure 6a shows the heatmap for the distribution of the targets and place of study. As can be observed in Fig. 6a, a total of 133 articles discusses substance misuse in the USA. In contrast, most of the African countries, Greenland as well as some parts of South America are not studied. This is not unexpected for Greenland because the low population and polar climate result in a small market and a prohibitive supply chain therefore making the misuse of drugs less concerning issues. The annual prevalence of drugs misuse in South American countries are significantly lower than in North American countries (UNODC, 2023), thus highlighting that drugs misuse may not be pressing issues there overall. However, this gap also highlights the possibility of underreporting or insufficient resources and data for specific regions. This is perhaps especially true for Africa where a large portion of countries in the continent are not considered in the study of spatiotemporal analysis for narcotics-related activities despite being reported by WHO African Region that there are substantial substance misuse crimes happening in Africa (WHO African Region, n.d). The only African countries which are considered for mapping substance misuse crimes based on the 323 documents are Morocco, Nigeria, Kenya, Tanzania and South Africa. UNODC (2023) has recently revealed the statistical annex on the prevalence of drugs misuse according to the parts of each continent. It was found that the USA, situated in North America has almost equal amount of prevalence as the whole African continent. Despite having similar prevalence, the research is more focused in the USA than African countries. This further highlights issues that may be due to insufficient resources.

Fig. 6: Targeted country of study.
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a Heatmaps of targets and place of study for spatiotemporal analysis of narcotics-related activities. b Heatmaps of targets and place of study for spatiotemporal analysis of narcotics-related activities excluding USA.

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Due to the USA being highly focused on, the distribution for other countries cannot be discerned visually. Therefore, another heatmap is presented in Fig. 6b excluding USA. From Fig. 6b, we can identify that spatiotemporal analysis for substance misuse crime are often conducted in Asian countries but rarely conducted in African countries. Furthermore, a considerable amount of study were conducted in Mexico, Australia Canada, China and Iran, Iran, followed by India, Malaysia and United Kingdom. From both Fig. 6a, b, it can be clearly observed the existence of huge imbalance in the substance misuse crime mapping field. It is suggested to focus on other countries, especially those in Africa.

RQ 7 – Current popular research and future trend of research

The focus of the current 136 research documents can be represented by developing a word cloud consisting of common keywords found in each document (Fig. 7). The word cloud that represents the current research revealed that four words and/or phrases – spatial analysis, drugs, GIS and geography – have higher frequencies. This shows that the current research leans towards investigating the spatial relationship between drugs misuse and its associated issues, including HIV, by using some form of spatial analysis including geographic information systems (GIS).

Fig. 7
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Word cloud for keywords.

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Identifying the future directions in the investigation of narcotics-related activities using spatiotemporal analysis can help researchers to better navigate their research in line with the current needs in the world whether to investigate on overdose cases (Barboza et al., 2022; Bozorgi et al., 2021; Campo et al., 2020; Davlasheridze and Goetz, 2021; Des Jarlais et al., 2019; Hu et al., 2022; Liu et al., 2023; Marotta et al., 2019; Ransome et al., 2020; Ray et al., 2023; Rooney et al., 2018; Rostami et al., 2023; Sauer et al., 2021; Stopka et al., 2023), on wastewater analysis (Castiglioni et al., 2015; Vazquez-Roig et al., 2012), on relationship of violence with illicit drug use (Banerjee et al., 2008; Lum, 2008, 2011; Morris, 2013; Saucedo De La Fuente and Berry, 2019; Silveira Neto et al., 2023) and so on. In order to identify which of the area of research to focus on, three tools – thematic evolution, thematic map, and clusters by sources coupling were used to identify the future research trends for these topics of interest.

Figure 8 shows the evolution of research themes from 1974 to 2008, 2009 to 2014, 2015 to 2019, 2020 to 2022 and 2023 to 2024. The themes started with the initial use of GIS for the spatial analysis of drug use and HIV, to major use in GIS in mapping drug use in Mexico, to the harm reduction in substance use, to the drug overdose and cannabis use in Iran, and finally to the harm reduction in drug overdose due to cannabis.

Fig. 8
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Keywords transition from 1974 to 2024.

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Other than thematic evolution, thematic maps that categorize keywords into four themes—niche, emerging or decline, basic and motor, which are developed based on the development and the relevance degrees can be utilized. Generally, the studies focus on spatiotemporal analysis and obtaining geographic distribution of cocaine misuse, as seen in basic themes, in Fig. 9. In niche themes, the well-developed yet isolated themes such as mass spectrometry, drug products and liquid chromatography can be found. Under emerging or decline themes, the illicit and street drugs themes can be identified. The future direction of the research related to spatiotemporal analysis of narcotics-related activities can be identified under motor themes. It is common for people who inject drugs (PWID) to contract HIV, thus needing further research focus on the infection and mapping the demography of the PWID.

Fig. 9
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Thematic map based on development and relevance degrees.

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Conclusions

Narcotics-related activities that include but are not limited to misusing, possessing, distributing or positive urine drug tests is endemic to many countries although each may have their own country-specific variations. The latest research documents have focused on specific countries or regions and bounded by time frame. This paper managed to not be specific location and timewise for a comprehensive bibliometric analysis. With this big-picture scenario, we were able to extract insights from 323 documents in the Scopus database regarding the use of spatiotemporal techniques to map narcotics related activities. This bibliometric analysis identified several key points in the literature that allowed us to provide suggestions for the direction of future research.

This bibliometric study was able to pinpoint authors such as Dansereau, Cheung, Cooper, Grunewald and Ross as important and prolific authors in investigating narcotics-related activities using spatiotemporal methods. The Substance Use and Misuse has been identified as one of the top and “core” sources for publishing documents related to narcotics-related activities using spatiotemporal approach. Furthermore, documents authored by USA, United Kingdom and Australian researchers tend to get cited more. This suggests that impact and citation growth can be cultivated by collaborations with from USA and United Kingdom authors (see Table 9). Based on the popular keywords and thematic approach, we highlight that future research should focus on lowering the harm caused by cannabis overdose. This study has also identified a huge imbalance in research that use spatiotemporal techniques to map narcotics related activities where the major focus is on the USA and excludes many other countries and regions, especially African countries. More resources need to be channeled in mapping substance misuse crimes in African countries and further alleviate their health and well-being, in line with SDG Target 3 and Target 16.

This study is not without limitations. Firstly, the search query is used for TITLE field only so that the documents obtained is completely or almost completely related to what we need. However, TITLE-ABS-KEY or ALL fields may be used, however these queries may lead to hundreds of thousands of research documents. This will definitely be time-consuming and less productive. In this study only 0.7% of documents (323 documents out of 45,926 total documents) were considered.

Next, the bibliometric analysis was conducted by extracting pertinent research documents published in Scopus-indexed journals. Future research may attempt to incorporate Web of Science and Google Scholar databases in order to obtain a more comprehensive analysis. This is to further allow research documents that are written in various languages. However, cautions have to be exercised when calculating citation counts and top relevant publication outlets. Besides that, this study can be further improved by expanding the scope to better reflect the complex nature of narcotics related crimes by developing scoping review or systematic literature review.