Illicit drug use (IDU) globally has risen, with approximately 284 million people engaging in substance abuse, marking a 26 percent increase over the past decade, particularly affecting those under 35. Various regions show differing preferences for illicit drugs, such as cannabis in Africa and South/Central Europe, opioids in Eastern/Southeastern Europe and Central Asia, fentanyl in the US/Canada, and methamphetamine in Southeast Asia (UNODC, 2022). In 2018, Nigeria reported alarming rates, with 14.4% of the population (14.3 million people) involved in drug abuse, ranking the country among the world's leaders. Cannabis, opioids, and cough syrup were prevalent substances, with higher usage among men (21.8%) and the 35-39 age group having the highest prevalence at 50.8% (UNODC, 2022).

IDU among general populations is a pressing public health concern, contributing to psychiatric disorders, suicides, disability, and mortality, with over 11.8 million annual deaths attributed to IDU (Ritchie & Roser, 2019). Beyond health impacts, drug influence correlates with increased criminal involvement, posing safety risks and substantial economic losses exceeding $120 billion for treatment and incarceration (Martin, 2021). While existing research highlights social determinants of IDU (Osayomi et al., 2021; Mougharbel et al., 2021; Jumbe et al., 2021; Amaro, 2021; Browne et al., 2022; Mohammednezhad et al., 2020; Wu et al., 2020; Akande et al., 2023), a notable gap exists in understanding the influence of financial inclusion (FI) (i.e., access to, and the use of financial services) on this issue. This study addresses this gap by employing geographical techniques to analyze the spatial pattern of IDU in Nigeria and assess the association between FI, social factors, and drug use. The findings aim to contribute valuable insights for addressing the adverse health outcomes associated with illicit drug consumption (Adediyan, 2020; Finkelstein et al., 2012).

The 2021 World Bank report indicates global improvement in FI, with a 50% increase in account ownership from 2011 to 2021, reaching 76% of adults globally (World Bank, 2021). Mobile money access, particularly in developing countries, contributed to this growth. However, regional disparities persist, with Europe and North America leading at over 89% of FI, while sub-Saharan Africa lags below 50% (World Bank, 2021). In Nigeria, 55% of the population is financially excluded, with northern states facing challenges due to high illiteracy and religious constraints (Adeleke & Alabede, 2021; Muhammad et al., 2018). Southern states, particularly Lagos, Oyo, Ondo, and Osun, exhibit higher FI due to financial literacy and institutional concentration (Adeleke & Alabede, 2021). Gender disparities exist, affecting women in Nigeria due to low income and cultural barriers (Anyanwu et al., 2018). Additionally, FI varies between urban and rural areas, with rural areas experiencing lower FI due to small transaction volumes and unstable income (Nwanne, 2015).

Several studies emphasize the crucial role of FI in enhancing health and well-being. Research conducted in Nigeria by Ajefu et al. (2020) reveals a strong positive impact of FI on mental health, acting as a mechanism to alleviate depression symptoms. FI provides peace of mind, enhances household welfare by improving financial security, and reduces stress, aligning with findings from Aguila et al. (2016) and Patwardhan (2022). Additionally, Gyasi et al. (2019) and Finkelstein et al. (2012) demonstrate that FI reduces the risk of depression, psychological distress, anxiety, and overall poor health outcomes by diminishing poverty, which is linked to adverse health results. Lack of access to financial services, as highlighted by Buttrick et al. (2017) and Purtle (2020), can lead to depression and decreased life satisfaction.

Empirical evidence also links FI to population health, highlighting its role as a determinant in illicit drug use and substance abuse. Peckham (2022) shows that individuals with poor mental health, particularly depression, are more prone to developing substance use disorders. Approximately one-third of those with poor mental health engage in substance abuse, often as a means of self-medication to numb feelings of despair or cope with anxiety, as suggested by Osbourne (2022) and Lodge (2023). Given the evident positive impact of FI on health and well-being, this study argues for increased scholarly attention to explore how FI could contribute to reducing illicit drug use.

Social factors significantly impact IDU. Education plays a pivotal role, with studies showing that higher education levels correlate with a decrease in IDU, emphasizing the importance of imparting knowledge about substance abuse's adverse effects (Michael, 2020). In the United States, individuals without high school degrees exhibit the highest rates of IDU, underscoring the connection between education and substance abuse (NIDA, 2017). Age is another determining factor, with adolescents and young adults being particularly vulnerable due to peer pressure and limited understanding of associated risks. However, recent studies highlight a growing prevalence of substance abuse among older adults, often linked to coping with factors such as grief, loss, declining health, homelessness, or divorce (NIDA, 2020; Edwards et al., 2018).

The relationship between unemployment and IDU is complex, yielding conflicting results. While unemployment may contribute to the prevalence of IDU through heightened psychological distress, it could also decrease it, due to lower incomes (Nagelhout et al., 2017; Dubanowicz & Lemmens, 2015). High population density is associated with IDU, reflecting significant wealth disparity and increased exposure to life stressors in densely populated areas (Spiller & Lorenz, 2009). Furthermore, internet access has emerged as a notable factor, with research indicating a connection between online content glorifying drug use and increased substance abuse among young individuals. The Internet facilitates access to illicit drugs by connecting buyers and sellers, contributing to the rise in substance abuse, particularly among the youth (Preston, 2022; Adejoh et al., 2020). Income is a significant predictor, with higher drug use observed among high-income earners, although substance abuse transcends all income groups (Janicijevic et al., 2017; Ren, 2018).

Following the literature review, little scholarly attention has been given to the effect of FI on IDU. To this end, the study seeks to analyse the spatial relationship between the prevalence of IDU and FI through geospatial techniques. By mapping the geographical distribution and identifying hotspots, the research will investigate how social factors, demographics, and socioeconomic conditions influence the spatial patterns of IDU. The results will guide targeted interventions and policy development, considering spatial dynamics, disparities, and the efficacy of current strategies. Ultimately, our study aims to offer spatially informed recommendations to policymakers and stakeholders for addressing IDU and improving financial inclusion.