Worldwide, drug use and drug dependence are increasing significantly, with 296 million people using drugs globally [1]. This represents a 23% increase over the past decade. Most people who use drugs (PWUD), approximately 78%, reside in low- and middle-income countries and are concentrated predominantly in urban settings [2, 3]. Moreover, among people who use drugs, the number of individuals with a drug use disorder increased by more than 12 million in 2022 [4]. Substance use and drug dependence therefore pose significant global challenges, particularly because they are often associated with crime and place additional burdens on already strained public health services. Globally, approximately 11 million people have engaged in injecting drug use, and the prevalence of PWID has shown a consistent upward trend since 2017 across various regions. In Latin America, estimates range from 1,392,000 to 2,380,000; in Central Asia, from 400,000 to 510,000 [5]; and in South Asia, from 783,500 to 1,263,000. These growing numbers underscore the expanding impact of addictive behaviors across countries, with low- and middle-income countries being especially affected [5, 6]. Moreover, approximately 1 in 8 PWID (1.4 million) are living with HIV (UNODC World Drug Report, 2020), while 39.4% have viremic HCV infection [7]. Populations at high risk for HIV/AIDS include PWID, men who have sex with men (MSM), and female sex workers (FSW). These groups continue to contribute to the burden of HIV/AIDS, emphasizing the need for immediate, targeted interventions that address the distinct needs of each population [5].

Geographically, the prevalence of PWID is relatively higher in towns and urban areas than in rural areas [2]. Although African countries have historically reported low rates of injecting drug use, this pattern has shifted over the past 25 years, with heroin injection increasing in large towns in Kenya, Uganda, and Tanzania since 2009 [8]. The prevalence of injecting drug use has notably increased in East African countries, particularly Tanzania, Kenya, and Rwanda. This increase has had detrimental effects on quality of life and has increased the risk of blood-borne diseases and sexually transmitted infections, including HIV [9–12]. Notably, vulnerability to HIV is pronounced among groups such as MSM, FSW, and PWID, who currently exhibit high HIV prevalence [11, 13, 14].

The relationship between PWID and HIV/AIDS is well established, as surveys in India and China have demonstrated links between HIV/AIDS and drug use, including alcohol and other substances [6, 15]. Currently, the association between HIV/AIDS and injecting drug use remains an important public health concern, particularly given the high HIV prevalence among these populations [9, 11, 13, 14].

Many factors have been identified as increasing HIV/AIDS risk among this population. For example, sharing injecting equipment among PWID serves as a significant route for the transmission of HIV and other blood-borne diseases. A comprehensive systematic review that screened 55,671 papers and reports and extracted data from 1,147 eligible records documented substantial evidence of injecting drug use [2, 5]. This phenomenon was documented in 179 of 206 countries or territories, covering 99% of the population aged 15 years–64 years. According to the Centers for Disease Control and Prevention (CDC, 2021), approximately 1 in 10 new HIV infections can be attributed to injecting drug use [16]. These findings underscore the global impact of injecting drug use on HIV transmission and emphasize the urgent need for targeted interventions and public health initiatives [16].

According to the preceding literature, PWID can be influenced by a multitude of interconnected factors [2]. Factors associated with injection drug use encompass a range of experiences, from engagement in sex work and a history of sexual abuse to exposure to trauma and violence, social disadvantage, family history of drug use, and incarceration [17–19]. Social environments play a significant role, as peer pressure and the prevalence of drug use within communities can sway individuals toward injecting drugs. Mental health also plays a pivotal role, with conditions such as depression, previous substance use, trauma, adverse childhood experiences, anxiety, or trauma leading some to seek solace in substances [20]. Genetics may contribute, as certain individuals might be more genetically predisposed to addiction (NIDA, 2023). Access to drugs, whether through social circles or easy availability in illegal markets, can increase the likelihood of drug use. Socioeconomic factors, including poverty and a lack of opportunities, might drive individuals toward substances as a means of escape [17, 18]. Additionally, cultural influences and media representations can normalize or glamorize drug use, potentially influencing individuals’ ability to experiment with or resort to injecting drugs [19].

Depression has emerged as a widespread public health concern globally [21]. However, rates of depression vary across communities, with an increasing trend observed among PWID in several East African countries, including Kenya [22]. In Rwanda, depression affects 35% of genocide survivors and 20% of the general population [23]. Additionally, individuals living with HIV/AIDS in Rwanda experience depression, which is often associated with stigma and medication nonadherence [24]. Some individuals experiencing depression or other mental health concerns may turn to substance use, including injecting drugs, as a means of coping with emotional distress or self-medicating [25].

Harm-reduction or risk-minimization strategies targeting the behaviors of PWID in Rwanda have received limited attention and promotion. Recent research by Twahirwa Rwema et al. on injecting drug practices and HIV infection in Kigali identified bisexuality and initial needle sharing as significant risk factors associated with subsequent needle sharing and the transmission of blood-borne infections; therefore, the study advocated for increased implementation of harm-reduction practices [12]. However, to our knowledge, research on determinants associated with PWID in Rwanda remains limited. This gap may be partly related to the stigma and taboo surrounding injecting drug use, which is often perceived as illegal or socially unacceptable. Such perceptions can marginalize PWID and create barriers to their social inclusion and coexistence with the broader population [2]. This study aimed to explore the relationships among sociodemographic characteristics, substance and alcohol dependence, and depressive symptoms among PWID and to examine factors associated with PWID status within a sample at high risk for HIV/AIDS in Kigali, Rwanda. By addressing these relationships, this research seeks to fill critical gaps in understanding the complexities surrounding drug-use behaviors and their psychosocial implications within this context.

The findings of this study revealed a high prevalence of depressive symptoms among participants at high risk for HIV/AIDS in Kigali, Rwanda. Overall, 86.25% of participants reported depressive symptoms, and most PWID had moderate to severe symptoms. A 2015 study by Li et al. in China supports our findings, showing that injecting drug use is closely associated with depression and other mental health problems [27]. Depressive disorders are commonly associated with addiction. Some people may inject drugs while experiencing depression, whereas others report that injecting drug use contributes to depressive symptoms [21, 27, 28]. The high prevalence of depressive symptoms in Rwanda is not a new phenomenon. The post-genocide period in Rwanda has been characterized by a high prevalence of depression within the community. Recent studies have shown that poor mental health is common across demographic groups in Rwanda [23, 25]. Nevertheless, the prevalence of depressive symptoms among PWID (94%) and among participants in other groups at risk for HIV/AIDS (82.3%) far exceeds previously reported rates of 35% among genocide survivors and 20% in the general population [23].

Our study revealed that participants’ age and sexual orientation were associated with PWID status in the bivariate analyses. For example, younger participants and sexual minorities, particularly MSM and FSW, were more frequently represented among PWID. Our findings align with previous research conducted in Africa, including a study in Kenya that documented heroin injection among young women engaged in sex work and men from sexual minority groups [28].

Regarding mental health, our results showed that participants with depressive symptoms were more likely to be PWID than those without depressive symptoms. This finding is consistent with the self-medication hypothesis, whereby the co-occurrence of depressive symptoms and limited access to mental health resources in low-income settings may be associated with substance use, including injection drug use, as a coping strategy [9]. However, given the cross-sectional design, the reverse pathway is equally plausible: substance-induced depression, such as during withdrawal from opioids or stimulants or as a neuroadaptive consequence of chronic use, is well documented in the neuropsychopharmacology literature, and injecting drug use may itself contribute to depressive symptoms rather than result from them. Moreover, the illegality and stigma surrounding injecting drug use may discourage individuals with co-occurring depressive symptoms from seeking mental health assistance. This interplay between depression and limited mental health support in Rwanda may heighten vulnerability to injecting drug use as a means of coping. These findings are consistent with previous studies [29].

As this was a cross-sectional study, we cannot determine which behavior occurred first. It is often assumed that individuals using other drugs may progress to injection drug use over time. Thus, it is not surprising that substance-use behaviors, particularly marijuana use, were associated with PWID status. These findings align with an earlier study conducted in China among women who injected drugs and also engaged in sex work. Those studies highlighted that these women had a greater likelihood of experiencing suicidal ideation, engaging in risky behaviors, and using alcohol and other substances [21, 30]. Clients of sex workers provided them with drugs and frequently shared injecting equipment. Corroborating these findings, a survey conducted in the Saskatoon Health Region in Canada revealed that initiation of substance use often begins in childhood and is influenced by networks of PWID, including friends and schoolmates [31]. Notably, Rwanda has a predominantly young population, and many participants in our study were younger than 25 years. These results indicate substantial substance use among younger participants, although age at initiation was not explicitly explored in our research.

A recent study of injecting drug practices and HIV/AIDS among PWID revealed that 99% of PWID primarily used heroin, 91% had shared needles in their lifetime, and 31% had shared needles in the previous 6 months. HIV prevalence was 9.5%, and needle sharing and other risky behaviors, such as reusing needles and sharing drug paraphernalia, significantly increased risk, particularly among women in Rwanda [12, 25]. We also found that depressive symptoms, alcohol and substance dependence disorders, and a history of seeking substance-use treatment were significantly associated with injection drug use. These findings are consistent with previous studies conducted among fisherfolk in China and other groups in Vietnam, Tanzania, and Kenya, which showed that adolescents of both sexes and sexual minorities, including FSW and MSM, are more likely to engage in injection drug use [21, 27, 30]. A recent study of injecting drug use in Rwanda by Rwema et al. (2022) established an association between injecting drug use and HIV/AIDS. However, that study did not examine how depressive symptoms were associated with injection drug use. Our findings indicate that a considerable proportion of Rwandan youth who inject drugs report depressive symptoms. Such behavior may serve as a coping mechanism to escape or alleviate depressive mood.

Although substance use was high overall, our results indicated that PWID in our sample were more likely to meet criteria for drug dependence than for alcohol dependence. Nevertheless, both drug and alcohol dependence were associated with injecting drug use. Drug use may progress from alcohol or non-injection drug use to injection drug use over time. PWID may use other types of drugs through different routes, including sniffing cocaine and using marijuana, in addition to alcohol use [9, 15].

Finally, 4.7% of participants in our study were HIV positive. This finding indicates that our sample, which was recruited because it included individuals at greater risk for HIV/AIDS, had a higher HIV prevalence than the approximately 3% reported among Rwandan adults aged 15 years –49 years [32]. However, the somewhat unexpected finding that HIV prevalence among PWID was lower (2.6%) than among the other risk groups in the study (5.7%) warrants cautious interpretation rather than reassurance. Because PWID in our sample were significantly younger than non-PWID participants (52.3% vs. 42.6% aged 18–25 years), the lower observed HIV prevalence among PWID may reflect shorter cumulative exposure time rather than a true reduction in risk. Age-stratified or age-adjusted comparisons are needed to disentangle these effects before concluding that intervention has averted HIV acquisition in this group; we identify this as a priority for further analysis (see Limitations).

Two previous studies of HIV-positive PWID reported a high prevalence of depressive symptoms in this group, ranging from 42% to 44% [33, 34], which was lower than the prevalence observed in our study. Both studies identified depression as a factor associated with PWID among HIV-positive individuals. Depressive symptoms and mental health disorders are not new among people who use illicit drugs; however, the types of substances used can affect symptom severity. For example, research conducted in Mwanza, Tanzania, revealed that heroin users were more likely to engage in unprotected sex, thereby increasing exposure to HIV/AIDS and other blood-borne diseases, which can contribute to depression [35].

Our findings differ from the prevailing literature, as family background was not statistically associated with injecting drug use. This contrasts with European research findings in which more than half of participants reporting frequent domestic conflicts had a family history of substance use, and three-fourths had peers engaged in injecting drug use [36]. The absence of such associations in our results may be attributable to the relatively underexplored nature of injecting drug use, which represents a rapidly evolving trend in African countries, including Rwanda. Compared with other forms of substance use, injecting drug use is a relatively new phenomenon in this context, and familial influences on this specific route of drug administration are not yet well understood.

In contrast to the patterns observed for injecting drug use in this study, family members in Rwanda may influence their offspring in matters related to substance use [37]. Substance use by a family member may affect a child through mechanisms such as increased genetic predisposition or negative role modelling, thereby heightening the child’s susceptibility to substance use [38]. In Rwandan culture, as in many other societies, children may emulate behaviors demonstrated by their parents, and substance use, including drinking and smoking, can reflect a familial culture of use.

This study provides important evidence on the intersection of depressive symptoms, substance use, and injecting drug use among individuals at high risk for HIV/AIDS in Kigali, Rwanda. A high prevalence of depressive symptoms was observed, particularly among PWID, and depressive symptoms, alcohol and substance dependence, and previous treatment for substance use were significantly associated with PWID status. Younger participants and sexual minority groups, including MSM and FSW, were also more frequently represented among PWID. These findings highlight the overlapping mental health, substance-use, and social vulnerabilities associated with injecting drug use in this setting.

Given the cross-sectional design, these associations should not be interpreted as causal relationships. The results from this work nevertheless underscore the importance of integrated health services that address mental health, substance use, and HIV-related vulnerabilities, particularly among younger and socially vulnerable populations. Future longitudinal and mixed-methods research involving larger and more diverse populations, including settings beyond Kigali, is needed to clarify the temporal relationships among depressive symptoms, substance use, injecting drug use, and HIV-related risks. Such evidence can support the development of contextually responsive harm-reduction and mental health strategies for PWID in Rwanda.