The Global Distribution and Epidemiology of Psychoactive Substance Use and Injection Drug Use Among Street-Involved Children and Youth: A Meta-Analysis

Abstract Background: Globally, street-involved children and youth (SICY) who work and live on/of the streets are at higher risk of increased psychoactive substances and injecting drug use. Objectives: The present study aimed to identify the prevalence, distribution, sociodemographic factors, and risk-taking behaviors associated with psychoactive substances and injecting drug use among SICY. Methods: Studies in English published from December 1 1985 to July 1 2022, were searched for on PubMed, Scopus, Cochrane, and Web of Science to identify primary studies on psychoactive substances and injecting drug use among SICY. The pooled-prevalence estimates were obtained using a robust fixed-effects model. Results: The most commonly reported life-time and current psychoactive substance was tobacco followed by cannabis, LSD/ecstasy, cocaine, methamphetamine, heroin and injection drug use. The results showed that life-time and current prevalence of methamphetamine and cannabis use, as well as life-time prevalence of cocaine, LSD/ecstasy, heroin, tobacco, and injecting drug use increased as age rose while current prevalence of cocaine and tobacco use decreased as age rose. SICY who were male, homeless, had parents who had died, had history of substance use among family members or best friends, had experienced violence, had casual sex partners, had a history of working in the sex trade, and had unprotected sex were all related to psychoactive substance use and injecting drug use. Conclusions: Research examining this population suffers from lack of studies, therefore, improving the knowledge for interventions aimed at reducing risk behaviors, particularly those related to the transmission of sexually transmitted infections such as HIV is of great importance.


Introduction
Many children around the world live on the streets and struggle with difficulties to survive (Keeley, 2021). Children living and working on the street are categorized by the United Nations Children's Fund (UNICEF) as follows: 'children on the street' , 'children of the street' , and 'children from street families' (World Health Organization, 2000). Children on the street work some hours of the day on the street, to contribute to their family financially, but often return home at night, and have familial ties (UNICEF, 2006). Children of the street both work and sleep on the streets and do not have a regular contact with family members (UNICEF, 2006).
Children from street families live with their families in the street (World Health Organization, 2000).
The phenomenon of street-involved children and youth (SICY) is quite diverse and varies between high-income and low-to middle-income countries (Zarezadeh, 2013). In developed countries, youth become street-involved because of familial conflict and child abuse (Embleton et al., 2016). However, children in low income counties may experience the street life due to abject poverty, child abuse, neglect, familial dysfunction, death of parents, war, and socio-cultural and religious beliefs (Cumber & Tsoka-Gwegweni, 2015;Woan et al., 2013). In addition, the psychoactive substance use habits usually vary from different countries (Embleton et al., 2013). In high-income countries, youth who live on the streets may be using injection drugs and other psychoactive substances that are not used commonly among children and youth on the streets in low income countries (Chettiar et al., 2010;DeBeck et al., 2013;Tozer et al., 2015).
Several sociodemographic factors and high-risk behaviors associated with psychoactive substance use and injection drug among SICY have been identified previously. Regarding sociodemographic factors, older age (Ayenew et al., 2020), male gender (Ahamad et al., 2014;Hadland et al., 2011), low educational status (Dejman et al., 2015), and family substance use (Ayenew et al., 2020) have been positively associated with psychoactive substance use and injection drug, among those attending the fifth grade and above (Ayenew et al., 2020). Presence of family members (Moura et al., 2012) has been negatively associated with psychoactive substance use and injection drug among SICY. Concerning high-risk behaviors, domestic violence and peer pressure (de Carvalho et al., 2006), best friend substance users, and staying more than one year on the street (Ayenew et al., 2020) have been positively associated with psychoactive substance use and injection drug among SICY.
To the best of the present authors' knowledge, studies related to street children and their drug use behaviors have mostly focused on investigating the prevalence and types of psychoactive substances used. The reported prevalence estimates are inconsistent and often very diverse within countries and geographical regions. There is only one previous meta-analysis that has been conducted among street children in resource-constrained settings (Embleton et al., 2013). As well as being over a decade old, the study (i) only reported psychoactive substance use among SICY in resource-constrained settings (not all countries all over the world), (ii) only reported life-time use of some specific substances such as alcohol, inhalants, and tobacco (i.e., not all psychoactive and injection drug use), (iii) did not report the pooled prevalence of substances per country (they reported the pooled prevalence of substances per continent), and (iv) did not run any subgroup analysis by age and time of publication. Also, there are no reported pooled data on the prevalence and types of psychoactive substances used and injection drug use by categories such as geographical region, or the characteristics associated with SICY's psychoactive substances used and injection drug use and their reasons for use.
In addition, no previous systematic reviews or meta-analyses concerning the prevalence of substance use in terms of age and year of publication year of studies have been conducted. Epidemiological information focusing on psychoactive substance use among SICY as well as its associated factors is required to improve the knowledge regarding the problem. Such data would contribute to programs designed for reintegrating children into communities. Therefore, the present systematic review and meta-analysis aimed to determine the prevalence, distribution, sociodemographic factors and risk-taking associated with psychoactive substances and injecting drug use among SICY.
The present study hypothesized that: (i) psychoactive substance use and injecting drug use would increase as age rose (H 1 ), (ii) psychoactive substance use and injecting drug use would decrease over time (H 2 ), and (iii) risky behaviors such as having experienced violence, having casual sex partners, having history of sex trade, and having unprotected sex would be stronger predictors of psychoactive substances and injecting drug use than socio-demographic factors (H 3 ).

Search strategy
Scopus, PubMed, Web of Science, and Cochrane library databases were systematically searched for English-language published articles and abstracts from December 1 1985 to July 1 2022. Also, Google Scholar was searched to identify any other relevant studies. The search strategy was prepared and modified for the various databases using important Boolean operators (AND/OR) with initial keywords: "(street children), (street youth), (homeless youth), (homeless children), (runaway children), (substance use), (substance abuse), (drug use), (psychoactive substances), (injection drug use)." The bibliographies of the selected full texts were also reviewed to check if there were any other relevant studies.
In case more than one study reported on the same sample of SICY, the most detailed data concerning the prevalence of drug use was selected. Supplementary File 1 presents the details of the search strategy, including the combination of keywords used in the different electronic databases.

Study eligibility, PECOs (participants, exposures, comparison, outcome, and study design) and exclusion criteria
The present systematic review was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2021). The PECOs criteria were used for: (a) participants: 'street-involved children and youth' were defined as any child (aged 0-18 years) or youth (aged 15-24 years) (Embleton et al., 2016) who spend a proportion or majority of their time living on the streets. Moreover, they may have been defined in studies as 'children on the street' , 'children of the street' , street children, working children, parking boys, or market children; (b) exposures: sociodemographic factors and risk-taking associated with psychoactive substance use and injecting drug use; (c) comparison: other street-involved children and youth); (d) outcomes: reporting original prevalence data on SICY's psychoactive substances and injecting drug use. Life-time psychoactive substances and injecting drug use including ever using a substance (at least one time) and current drug use (defined as drug use within the past 30 days); and (e) study designs: cross-sectional, cohort, case-control, mixed-methods, and interventions with baseline data were considered. Studies lacking original prevalence data were excluded from the study. Other exclusions included (i) studies which had high heterogeneity or outcome variations from the considered groups, and (ii) unpublished (i.e., non-peer-reviewed) theses (e.g., PhDs, Master's dissertations).

Study selection process and data extraction
Duplicate articles were deleted using EndNote X7 software. First, two authors (BA and RM) independently reviewed the titles and abstracts according to the study inclusion and exclusion criteria. Any disagreements between the two reviewers were resolved by a third author. In the second step, the full texts of studies were evaluated according to the eligibility study criteria. Data were then independently extracted by two authors (BA and RM) for the final selected studies according to: author, year of publication, country, study design, sample size, population details, associated sociodemographic factors and risk-taking, and psychoactive substances and injecting drug use assessment. If needed, selected study authors were contacted to provide further details. Cohen's Kappa statistic was used for agreement between two authors (Supplementary File 2). The agreement levels of poor, slight, fair, moderate, substantial, and almost perfect were considered by the values 0, 01-0.02, 0.021-0.04, 0.041-0.06, 0.061-0.08, and 0.081-1.00, respectively (Landis & Koch, 1977). Disagreements between two authors (less than 10% in total) were resolved by a third author.

Study quality assessment
The Newcastle-Ottawa Scale (NOS) (Peterson et al., 2011) was used to assess the quality of studies, which comprises three criteria: (i) the selection domain, including the representativeness of the exposed group, selection of the non-exposed group, and ascertainment of exposure (three items for cross-sectional studies and four items for cohort); (ii) the comparability domain, including group comparability based on the study design or analysis (one item each for both cross-sectional studies and cohort studies), and (iii) the exposure/outcome domain, including assessment of outcome (one item for of cross-sectional studies and three items for cohort). Studies were categorized as unsatisfactory, satisfactory, good or very good. There is possible maximum score of 8 for cohort and case control studies. Studies that reached a total score of 0-2 were "unsatisfactory," 3-4 were "satisfactory," 5-6 were "good" and 7-8 was "very good" respectively. In total, 26 studies were rated as high quality, 41 were rated as good quality, and 13 were rated as satisfactory quality (Table 1).

Data synthesis and statistical analysis
Life-time or current drug use prevalence for psychoactive substances and injecting drug (methamphetamine, cocaine, LSD/ecstasy, 1 cannabis, heroin, tobacco and injecting drug use) were considered by type of drug. Any reports of overall prevalence without mentioning the specific time period in the studies were considered as life-time use for the purposes of the meta-analysis. The pooled-prevalence estimates were obtained using a robust random-effects model (i.e. the DerSimonian-Laird method) (DerSimonian & Laird, 1986). In contrast to the more restrictive fixed-effect model such as Mantel-Haenszel method (Mantel & Haenszel, 1959), this model allows for obtain samples from heterogeneous populations. It also enables the obtained prevalence estimates to vary not only because of the random error within studies (as in the fixed-effects model), but also because of true variation from one study to another. Heterogeneity between studies was assessed using I 2 statistics, which evaluate the percentage of variation among studies (Langan et al., 2019). The study used fixed-effect model with a smaller number of studies (Borenstein, 2009;Lin et al., 2020). Also, both fixed and random effect models were run. The precision of each model was evaluated, and then the model which had most precision was reported. Mixed effects meta-regression was used to investigate the effects of potential factors (age and year of publication of studies) on the heterogeneity of psychoactive substances and injecting drug use among SICY.
To assess publication bias, Egger's approach was performed both graphically and statistically (Egger et al., 1997). A p-value of 0.05 was deemed to be statistically significant. Subgroup analyses were performed by age and year of publication of studies. A sensitivity analysis was conducted on the geographical data to evaluate the possible undue influence on the meta-analysis in each of the geographical categories. To visualize the different prevalence on the world map, the latitude and longitude values related to each country were extracted by geocoding using the geopandas Python package and the visualizations were conducted using folium library in python. All the codes were run on the Google Collaboratory research platform. The association between street-involved children and youth's substance use in resource constrained settings and sociodemographic factors and risk-taking were assessed by OR, and 95% CIs. The obtained results were visualized using forest plots. For data analysis, R 3.5.1 with the meta package was applied to perform the meta-analysis.

Study characteristics
Of the 11,121 articles found, 6,524 were duplicates, 3,706 were screened by title and abstracts, 548 were selected for full text review, and 80 were finally retained for systematic review ( Table 2). The main reasons for exclusion of studies were: 400 studies did not have a quantitative methodology and did not report odd ratios of relative risks of associated variables related to the study outcomes (85%), and 68 did not qualified according to minimum quality appraisal (15%) (Figure 1). Of the 80 studies, 35 were based on data collected from the America Region (n = 20,016 participants) and 22 from the Africa Region (n = 6,230 participants). Canada was the country with the highest number of included studies (24 studies and 13,672 participants). Considering the World Bank country income level, there were 27 studies from higher income countries (n = 15,328), eight studies from upper middle-income countries (n = 10,345), 41 studies from lower middle-income countries (n = 13,610), and four studies from lower-income countries (n = 1,111).
Study sample sizes ranged from 23 to 5,268 SICY, with 57 studies including both males and females, 10 studies with Table 1. Risk of bias assessment of the included studies using the newcastle-Ottawa Scale. Good males only, and 13 studies not reporting gender. SICY were more likely to be male (74.55% on average in the studies, varying from 50% to 100%), and on average were 16.22 years old. Almost two-thirds of studies were published between 2010 and 2022 (58%). Most studies were cross-sectional (64 of 80). More than half of studies (58%) utilized the UNICEF definition of street children for their inclusion criteria. Only 16 studies considered both children and youth on/of the street, 18 studies only considered children and youth of the street, 23 studies only considered children and youth on the street, and 23 studies did not report their samples in terms of children and youth on/of the street (Table 2). Table 3 presents the geographical distribution of life-time and current prevalence of psychoactive substance and other drug use among SICY. There were studies from 24 different countries and considering life-time and current prevalence rates of psychoactive substance use and other drug use, the majority (93%) were from Canada and (91.56%) and the US respectively (Table 3)

Pooled prevalence of life-time and current psychoactive substances and other drugs use among SICY
Meta-analysis showed that among SICY, the most commonly reported life-time and current psychoactive substance was tobacco followed by cannabis, LSD/ecstasy, cocaine, methamphetamine, heroin and injection drug use (Table 4 and Supplementary Files 17-30).

Subgroup analyses of pooled prevalence of life-time and current psychoactive substances and other drugs use by age of participants among SICY
A subgroup analysis was performed based on age of participants, categorizing the participants into three groups: (i) 10-14 years, (ii) 15-18 years, and (iii) >18 years. The results confirmed that life-time and current prevalence of methamphetamine and cannabis use, as well as life-time prevalence of cocaine, LSD/ecstasy, heroin, tobacco, and injecting drug use increased as age rose while current prevalence of cocaine and tobacco use decreased as age rose (Table 5 and Supplementary Files 31-41). Therefore, H 1 was only partially confirmed (because current prevalence of cocaine and tobacco use decreased as age rose among SICY).

Sociodemographic factors and risk-taking associated with life-time or current psychoactive substances and other drugs use among SICY
The analysis indicated that SICY who were males were 6.18 times more likely than females to have life-time or current substance use (OR = 6.18, 95% CI = 3.06, 12.49). Those who were homeless were 1.31 times more likely than those who were not to have life-time or current substance use (OR = 1.31, 95% CI = 1.21, 1.41). SICY whose parents had died were 1.19 times more likely than those who parents had not to have life-time or current substance use (OR = 1.19, 95% CI = 1.10, 1.29). Participants who had history of imprisonment were 1.32 times more likely than those who had not to have life-time or current substance use (OR = 1.32, 95% CI = 1.10, 1.58). Those who had substance users in their family were 2.48 time more likely than those who did not to have life-time or current substance use (OR = 2.48, 95% CI = 1.83, 3.36). Those who had best friends that were substance users were 4.14 time more likely than those who did not to have life-time or current substance use (OR = 4.14, 95% CI = 2.90, 5.91).
Those who were victims of violence were 1.37 time more likely than those who were not to have life-time or current substance use (OR = 1.37, 95% CI = 1.20, 1.56).
Those who had casual sex partners were 2.64 times more likely than those who did not to have life-time or current substance use (OR = 2.64, 95% CI = 1.98, 3.54). Those who had history of working in the sex trade were 1.89 times more likely than those who did not to have life-time or current substance use (OR = 1.89, 95% CI = 1.54, 2.31). Finally, participants who had unprotected sex were 3.27 times more likely than those who did not to have life-time or current substance use (OR = 3.27, 95% CI = 1.83, 5.86) (Figures 2 and 3). Therefore, H 3 was confirmed (i.e., risky behaviors were stronger predictors of psychoactive substance use and injecting drug use than socio-demographic factors) on the basis that far more studies show significant associations between risky behaviors and psychoactive (1-2%) a a number of studies have reported LSD/ecstasy as a combined category so this grouping has been retained for the present study's meta-analysis.
nR b a a number of studies have reported LSD/ecstasy as a combined category so this grouping has been retained for the present study's meta-analysis. b not reported. Methamphetamine nR b nR b nR b cocaine 13% (12-14%) 18% (104-23%) nR b LSD/ecstasy a nR b nR b nR b cannabis 73% (72-75%) 27% (25-29%) 34% (32-35%) Heroin nR b nR b nR b tobacco nR b 21% (19-24%) 61% (59-63%) injection drug use nR b nR b nR b a a number of studies have reported LSD/ecstasy as a combined category so this grouping has been retained for the present study's meta-analysis. b not reported.
substance use than significant associations between socio-demographic factors and psychoactive substance use.

Meta-regression
In order to investigate the effects of potential contributing factors on the heterogeneity of studies on pooled prevalence of life-time and current psychoactive substances and other drug use, meta-regression was used to study two specific factors (i.e., participants' age, and time of publication of studies). With increasing age of study participants, the pooled prevalence of life-time cannabis, cocaine, heroin, tobacco use and the pooled prevalence of life-time and current injection drug use increased, and was statistically significant (p < 0.05) (Tables 7 and 8). With increasing time of publication of studies, the pooled prevalence of current tobacco and injection drug use increased, and was statistically significant (p < 0.05) (Table 8).

Discussion
The present meta-analysis was conducted to estimate the pooled-prevalence estimates of life-time and current psychoactive substances and injecting drug use among SICY by geographical region as well as psychoactive substances and injecting drug use by age and year of publication. The present systematic review and meta-analysis found a high prevalence of psychoactive substances and injecting drug use among SICY with significant variation by geographical region and study methodology. No pooled prevalence for a majority of these psychoactive substances has previously been reported in relation to SICY. The pooled prevalence rates of cocaine, cannabis, and tobacco use were higher than the percentages reported in a previous meta-analysis (36% vs. 7% for cocaine; 45% vs. 31% for cannabis; and 51% vs. 44% for tobacco) (Embleton et al., 2013). H 1 and H 2 were only partially confirmed. The type of psychoactive substance used has a significant impact on the mortality and morbidity, and also has a major effect on social reintegration of the users (Lubman et al., 2008). The estimated pooled-prevalence rates in the present study are much higher than those of the World Health Organization (WHO) regarding life-time psychoactive substance use of non-street youth globally (World Health Organization, 2013). The present study's findings provide insight into the factors associated with psychoactive substance use and injecting drug use. In particular, psychoactive substance use and injecting drug use were associated with being male, being homeless, having parents who have died, having a history of substance use in the family or among best friends, being the victim of violence, having casual sex partners, having a history of working in the sex trade, and having unprotected sex. H 3 (that risky behaviors would be stronger predictors psychoactive substance use and injecting drug use than socio-demographic factors) was confirmed among SICY.
Substance use among males was reported to be 6.24 times more compared to females. The reason may be due to the lack of awareness among the boys about using substances (Kumar et al., 2008), as well as higher peer pressure (Bal et al., 2010) which is an important factor affecting illegal drug use, and other precipitating causes such as pleasure seeking, ways to overcome sadness, and "to get a sense of well-being" (Kumar et al., 2008;Njord et al., 2010;Seth et al., 2005). Peer pressure also results in children not feeling guilty about abusing inhalants (Praveen et al., 2012). According to the findings, homelessness was significantly associated with substance use. This may be due street-involved youth using drugs to stay alert while sleeping on the street (Bungay et al., 2006). This finding is consistent with a longitudinal analysis of adult injection drug users that reported a significant association between homelessness and initiating methamphetamine injection . Another cross-sectional study reported that methamphetamine use (at least daily) was associated with homelessness (Coady et al., 2007).
Deprived SICY are more likely to use psychoactive substances following parental death (Aviad-Wilchek et al., 2017). Children using substances do not typically live with their families therefore the lack of parental guidance and social and family involvement on such behavioral outcomes among juveniles are an important determining factor (Van Leeuwen et al., 2004). Studies have reported that children living with both parents and/or were closely monitored significantly by parents have lower alcohol, tobacco and/or substance use (Ledoux et al., 2002).
Having imprisonment history was associated with drug use among SICY. Previous studies have indicated that high-risk behaviors such as drug abuse among prisoners  (Kakchapati et al., 2018;Milloy et al., 2009). Therefore, suitable interventional strategies are recommended for prisoners.
The findings of the present study suggested that family's history of drug use was significantly associated with street children's drug use. This finding concurs with other studies (Hoffmann & Cerbone, 2002;Taplin et al., 2014). Therefore, families of street children have a significant effect on their drug use (Dejman et al., 2015). One study reported that the history of substance use among fathers was associated with psychoactive drug use among children (Seth et al., 2005). Also, several studies indicate that substance use in families has negative outcomes and is significantly associated with children's substance use (Lander et al., 2013;Roshanfekr et al., 2020). Therefore, the wide range of possible outcomes for these children is essential for policymakers who need to address family history of drug use and its consequences (i.e., risky behaviors) in the community. Correspondingly, youth who had best friends as substance users were five times more likely to use substances compared to those that did not. This finding was consistent with other studies (Ayenew et al., 2020;Moura et al., 2012). The reason may be due to the fact that older children use substances to avoid to avoid being stigmatized by their friends, to impress their friends and/or because of peer pressure.
The findings also suggested a significant association between substance use and being a victim of violence among street-involved youth, which is in line with previous studies (Chermack & Blow, 2002;Marshall et al., 2008). These studies have reported that violence experienced during adolescence is associated with alcohol-related consequences, and is a risk factor for alcohol use disorders in young adulthood (Grigsby et al., 2016). Also, sexual violence experience during adolescence may cause emotional and social impairments that lead to substance use (Noll, 2008). Such traumatic experiences which are common among street-involved youth, may increase the risk of subsequent hazardous alcohol use. Drug use may cause high-risk behaviors such as commercial sex work, exchanging sex for drugs, and forced sex that could expose individuals to HIV or other sexually transmitted infections and violence. However, little to no knowledge in this population about these behaviors and health outcomes is available.
According to previous studies, there are associations between drug and alcohol use and risky sexual behaviors (Baskin-Sommers & Sommers, 2006). Therefore, it is very important to determine their impact upon HIV and mortality risks. According to the results there was an independent association between substance use and having a steady sexual partner which may be the sign of unsafe sex, which may be a potential intervention opportunity in this young group. The reason might be because that having a steady partner is associated to lack of condom use due to the general belief about emotional commitment in relationships (de Carvalho et al., 2006;Silva, 2002) which may lead to the having unprotected sex (Silveira et al., 2002). Therefore, to reduce the sexual risk, interventions to increase condom use, better condom negotiation skills, and increasing the access to condoms are necessary. In the present study, substance use among street-involved youth was associated with sex work involvement which is in line with previous studies from various settings reporting the association between injection drug use and sex work among street-involved youth (Haley et al., 2004;Shakarishvili et al., 2005). Also, previous studies have indicated that involving in injection drug use and sex work places increase the risk of HIV infection and other sexually transmitted infections among street-involved youth Stoltz et al., 2007). The finding is also consistent with previous research reporting that injection drug users frequently engage in high-risk activities such as sex work to increase their income, and support their drug use or needs (DeBeck et al., 2007), and the sex work is often related to drug scene exposure (Stoltz et al., 2007).

Methodological considerations and limitations related to results
The studies included in the present systematic review and meta-analysis have some methodological concerns. First, two-thirds of the included studies were of a cross-sectional design, preventing the delineation of a causal/temporal association between the research variables under study. Second, most studies focus on the type and prevalence of drug use with limited statistical analysis. Further longitudinal studies are essential to determine the risk and protective factors of substance use among this susceptible population. It is recommended that the factors affecting street children's initiation, ongoing use, and ceasing of substances should be further investigated. Third, the reports of females in these studies were limited or did not include them at all. Therefore, more knowledge about street-involved girls and young women is necessary to avoid gender-based selection bias in this field of research.
Fourth, there was also a lack of available information on the physical and mental health outcomes that street children and youth can experience due to their misuse of multiple substances. Fifth, a number of studies did not follow the UNICEF definition for inclusion criteria regarding street children and included other children in their studies such as 'street-involved children and youth' which may reduce the comparability of the studies. This demonstrates the need for a universal and standardized definition of the 'street-involved child or youth' . Sixth, many studies did not use a unified definition of substance use as well as a definition of life-time or current substance use. Therefore, developing a clear definition of the burden of substance use and abuse in this population, life-time use from abuse and dependency, as well as current using patterns is needed. Improving reporting and defining variables more clearly would likely ensure more interpretable and effective conclusions. The creation of an updated valid and reliable substance use data collection tool to apply with SICY would ameliorate data collection and increase the comparability between studies.
Seventh, some variables included in the studies were not retained in the meta-analysis simply because there were data from no more than two studies (i.e., educational status, HIV infection, unable to access services, having mental health disorders). Eighth, the selected number of studies was arguably limited to the variables examined. Ninth, due to the sensitive nature of questions regarding substance use, the sampling and prevalence estimates may have been affected by social desirability biases and the relationship between the children and the interviewer and/or the questions asked. Due to the substance use habits, children may have mistrusted the interviewers and not answered correctly if it prevented their participation at a drop-in center or expulsion from a shelter/institution. Tenth, the search was restricted from 1985 to July 2022. Eleventh, grey literature including dissertations, research and committee reports, government reports, conference papers, ongoing research, manuscripts and unpublished studies were not included. This is because the research team was unable to evaluate the quality of these studies adequately. Finally, only English language publications were included in the study, therefore some relevant studies may have been missed.

Conclusions
The present study documented the evidence regarding substance use among SICY. It demonstrated the risk for psychoactive substance use and injection among SICY tended to increase with age. Research in this population suffers from lack of studies, therefore, improving the knowledge for interventions aimed at reducing risk behaviors, particularly those related to the transmission of sexually transmitted infections such as HIV is of great importance. Intervention should focus on the medical model (i.e., early intervention should not be directed at any one cause but should be multipronged) as well as improving the services including legal, administrative, social, and educational services for adolescent street children, their families, and communities. Also, various social support strategies should be applied to support and help these populations through living facilities, and education.
Since many of the youth living on the street do not have access to traditional services, strategies must be established for these participants in their natural environments. Street outreach programs could engage SICY into more intensive prevention and health services. However, the programs should provide not only condom distribution, bleach, and referrals but gender-specific techniques for decreasing both sexual risks and drug using risks. These approaches should complement the prevention services including a wider range of housing, healthcare, drug treatment, guidance, and employment facilities. Note 1. A number of studies have reported LSD/ecstasy as a combined category so this grouping has been retained for the present study's meta-analysis

Authors' contributions
BA-Conceived the study BA-collected all data. BA and RM-analyzed and interpreted the data. BA-drafted the manuscript. MDG and BA contributed to the revised article and were responsible for all final editing. All authors commented on the drafts of the manuscript and approved the final copy of the article for submission.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declaration of interest
The authors declare that there are no conflicts of interest.

Ethics approval and consent to participate
The present study was an analysis of preexisting literature and did not use human subjects.

Funding
The author(s) reported there is no funding associated with the work featured in this article.