Global patterns in age of substance use onset: a systematic review and meta-analysis of continental and temporal trends in 58 countries.

OBJECTIVE

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

METHODS

Following PRISMA guidelines (PROSPERO CRD42024596884), we searched PubMed, ISI Web of Science, PsycArticles, and Scopus in April 2024 without restrictions on study design or sampling method. Random-effects meta-analyses with multilevel modelling estimated pooled mean ages, and meta-regressions explored heterogeneity.

RESULTS

We included 304 studies comprising 771 samples. The estimated global age of onset was 16.1 years for alcohol (SE=0.2), 16.1 for nicotine (SE=0.2), 16.5 for cannabis (SE=0.2), and 17.2 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). Over decades, onset age increased significantly, particularly for alcohol (+0.06, p=0.013) and stimulants (+0.12, p=0.002). Geographically, onset 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), mean age of the sample (p<0.001), and risk level for problematic substance use (p=0.002) were also significantly associated with heterogeneity estimates.

CONCLUSIONS

Although onset age has increased in recent decades, South America consistently shows earlier initiation. These findings highlight persistent geographic and demographic disparities relevant for prevention policy.