OBJECTIVE: We systematically analyzed the age of substance use initiation across continents, examined temporal trends, and tested demographic moderators.

METHODS: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we searched PubMed, ISI Web of Science, PsycArticles, and Scopus in April 2024 without restrictions on study design or sampling method. We estimated pooled mean ages through random effects meta-analyses with multilevel modeling and explored heterogeneity through meta-regressions.

RESULTS: A total of 304 studies comprising 771 samples were included. The estimated global age of first use was 16.1 years for alcohol (standard error [SE] = 0.2), 16.1 years for nicotine (SE = 0.2), 16.5 years for cannabis (SE = 0.2), and 17.2 years for inhalants (SE = 0.6). Hallucinogens (18.4, SE = 0.5), amphetamines (20.5, SE = 0.4), sedatives (20.7, SE = 0.5), cocaine (20.8, SE = 0.3), and opioids (21.2, SE = 0.3) had significantly later onsets (p < 0.001). Age of first use increased significantly in recent decades, particularly for alcohol (+0.06, p = 0.013) and stimulants (+0.12, p = 0.002). Geographically, initiation occurred earlier in South America (-2.2 years, p = 0.004) and later in Asia (+2.1 years, p < 0.001). Demographic characteristics such as sex (p = 0.007), the sample's mean age (p < 0.001), and risk level for problematic substance use (p = 0.002) were also significantly associated with heterogeneity estimates.

CONCLUSIONS: Although the age of first substance use has increased in recent decades, earlier initiation has been consistent in South America. These findings highlight persistent geographic and demographic disparities that are relevant for prevention policies.