This meta-analysis offers a systematic review of substance use outcomes among first and second-generation immigrants and synthesizes evidence from 51 studies. The results varied by the type of substance and nature of use; however, overall, the second generation of immigrants demonstrated a higher risk of substance use compared to their first-generation counterparts. The risk was more evident for alcohol, drugs and cannabis, while differences were less notable for tobacco. Furthermore, gender-stratified analyses indicated a stronger association between generational status and substance use risk among second generation women. Our findings suggest a generational pattern in substance use risk, with SGIs being more vulnerable than FGIs, which remained robust across sensitivity analyses and was supported by subgroup and meta-regression results.

The current findings corroborate with previous research that identifies generational status as a contributing factor in health behaviors among immigrant populations such as substance use. A previous meta-analysis of studies conducted in Europe has demonstrated similar findings with an overall tendency toward increased risk of substance use for SGIs (Najdini et al., 2025). However, generational status should not be understood as an explanatory mechanism in itself, but rather as a marker of changing exposures, social and relational contexts across immigrant generations. Although cultural settings were not directly analyzed in our study, they may help explain the observed differences in substance use between generations. While our finding may be partly explained by acculturation theory defined as the process in which individuals change over time when exposed to another culture, this interpretation remains incomplete if acculturation is understood only as a linear process of cultural adoption. Contemporary assimilation literature instead shows that assimilation involves not only individual adaptation, but also changing social boundaries between immigrant-origin groups and the majority (Alba & Nee, 2009). Segmented assimilation theory further extends this argument by emphasizing that the children of immigrants are not incorporated into a single mainstream, but into different social contexts depending on different factors such as parental resources, family and community social capital, discrimination, socioeconomic opportunity, and modes of reception (Portes and Zhou, 1993, Portes and Zhou, 2025).

Empirical evidence supports this more differentiated interpretation. Canino et al. (Canino et al., 2008) and Eitle and al. (Eitle et al., 2009) show that substance use disorders among Latinos are shaped by the relational and community context in which assimilation occurs, including family language use, changes in family and social relationships, selective acculturation, and co-ethnic school context. Warner et al. (Warner et al., 2010), however, caution against viewing assimilation as uniformly risky, as they found higher alcohol use among immigrant Mexican-origin youth and no consistent association between several assimilation measures and alcohol use. At a broader level, a meta-analysis on immigrant generation and youth problem behaviors showed substantial heterogeneity in the immigrant advantage for externalizing behaviors such as substance use, reinforcing the need to interpret generational differences as context-dependent (Tilley et al., 2021). These findings suggest that SGIs substance use risk may be shaped by multiple and intersecting mechanisms, including host-country norms, peer exposure, family dynamics, intergenerational conflict, discrimination, and bicultural identity navigation (Hjern, 2004; Martinez, 2006; Salerno et al., 2019). Cultural gaps between immigrant parents and children may increase family conflict and affect mental health, while identity conflict or weak belonging to both heritage and host cultures may reduce social support and increase substance use as a coping response (Berking & Wupperman, 2012; Buchanan & Smokowski, 2009; Grigsby et al., 2018; Kim et al., 2021; Walsh et al., 2015). Ethnic identity may therefore be protective when it provides belonging and support, but may become source of stress when linked to marginalization or exclusion (Fisher et al., 2017; Holley et al., 2006). Structural and gendered factors may further shape these patterns. For example, socioeconomic resources appear to offer weaker protection for some second-generation groups (Okuyama et al., 2026), while gendered norms may influence both exposure to substance use and experiences of acculturative stress. Men are generally more likely to use substances, possibly due to peer exposure and weaker familial oversight, whereas women may experience specific forms of acculturative stress when gender norms differ between heritage and host-cultural contexts (Kulis et al., 2012; Molina et al., 2016; Vega et al., 1998; Wahl & Eitle, 2010). Additionally, parental immigration related trauma can influence readiness to engage in substance use behaviors (Aviad-Wilchek et al., 2017). A systematic review showed that trauma among refugee parents may be transmitted to their children through mechanisms such as insecure attachment, maladaptive parenting, impaired family functioning, and parental emotional unavailability (Flanagan & Johnsen, 2020). In this context, substance use may be used as a self-medication to manage stress and difficult emotions (Garland et al., 2013; Khantzian, 2013). Thus, the higher risk observed among SGIs may reflect not only increased cultural exposure to host-society substance use norms, but also the conditions under which this exposure occurs.

Our findings can be discussed in relation to cross-national differences in how immigrant background is defined and measured. Categories of ethnic, racial, and immigrant origin are shaped by national histories, legal frameworks, political traditions, and dominant representations of diversity, rather than being purely technical or universal (Rea & Tripier, 2008; Simon & Piche, 2012). Simon's work on ethnic statistics in Europe shows that countries rely on different indicators, including birthplace, parental birthplace, citizenship, nationality, ethnicity, religion, language, or broader migration background categories, which may capture different social status (Simon, 2012). This is particularly relevant where host-country-born status within a specific ethnic or racial group is used as a proxy for generational status. In such contexts, higher substance use risk may reflect not only generational acculturation, but also the position of native-born descendants who, despite formal integration, may continue to experience stigma, racialization, and exclusion (Simon, 2017).

Although native-born comparisons were not included, the lower levels of substance use observed among FGIs are consistent with patterns described in the broader literature on the “healthy immigrant effect”. However, this interpretation remains indirect, and the findings should primarily be understood as reflecting generational differences that can be explained by factors such as age at immigration, conservative cultural norms, religious prohibitions and strong family and community cohesion (Dillon et al., 2013; Kopak et al., 2012; Moreno & Cardemil, 2018; Revens et al., 2021). Evidence from prior studies suggests that religious involvement is often protective against substance use; however, its effectiveness may differ across cultural settings, and in some cases it does not prevent use (McAuslan, 2020; Sanchez et al., 2015). Another potential cause is the co-occurrence of substance use and mental health disorders particularly depression, anxiety and trauma exposure. Several studies have revealed particularly poor outcomes among certain groups of immigrants including forced migrants, undocumented migrants and refugees, for whom the migration journey is often challenging (Bustamante et al., 2017; Heptinstall et al., 2004; Peconga, & k., & Høgh Thøgersen, M., 2020). Thus, it is essential to consider the entire migratory trajectory including pre-migration, migration and post-migration conditions, as each one of these phases may contribute to substance use risk (Beiser & Hou, 2017; Li, 2016; Li & Anderson, 2016). Recent studies have shown that pre-migration trauma may exacerbate acculturative stress (Andisha & Lueger-Schuster, 2024; Barton et al., 2022). This is especially important knowing that immigrant populations are less likely to seek health care in general and mental health care more specifically in the host countries due to various barriers such as language difficulties, cultural stigma, limited awareness on available services and fear of potential deportation (Curtis et al., 2018; Satinsky et al., 2019; Scheppers et al., 2006).

Cultural context shapes substance-use risk, immigrants from low-consumption countries may retain abstinence norms longer, while those from high-consumption regions may have higher baseline use(K. G. Chartier et al., 2017; Cook et al., 2021b; Sordo et al., 2015). As shown in our meta-regression analyses, the social context of reception is also important in mediating the risk of use. Assimilation and integration should therefore not be understood as a linear process, but as trajectories shaped by race, class, institutions, discrimination, and ethnic resources (Rea, 2021). While integration, is often considered the most adaptive acculturation strategy and has been associated with better mental health outcomes (Berry, 1997; Choy et al., 2021), it does not depend solely on individual adaptation. The experience of Black Americans illustrates that citizenship, cultural proximity, and long-term residence do not guarantee inclusion when racism, segregation, and political exclusion persist (Rea, 2021). Thus, integration also depends on the host society's openness to diversity and on the institutional conditions that support equal participation and multicultural belonging.

Several limitations should be acknowledged. First, although no language restrictions were applied, the predominance of English-language studies may have introduced language bias, and the focus on substance use may have excluded broader mental health studies reporting relevant substance-related outcomes. Second, included studies differed in methodology, sample size, measurement tools, immigrant groups, and national definitions of immigrant background. Because categories such as first- and second-generation immigrants may not be conceptually equivalent across countries, pooled estimates should be interpreted cautiously. This issue is particularly important given the high heterogeneity observed and the predominance of studies conducted in the United States. Third, most included studies relied on cross-sectional and self-reported data, limiting causal interpretation and increasing the possibility of social desirability or underreporting bias. Finally, restricted access to raw data prevented adjustment for important individual and structural variables, including socioeconomic status, education, migration policies, welfare systems, and urban context. Since no comparisons with non-immigrant populations were included, conclusions should remain limited to generational differences within immigrant groups.