Importance: Illicit and nonmedical (use in ways other than instructed) drug use is common in adolescents and young adults and increases the risk of harmful outcomes such as injuries, violence, and poorer academic performance.
Objective: To review the benefits and harms of interventions to prevent illicit and nonmedical drug use in children, adolescents, and young adults to inform the US Preventive Services Task Force.
Data sources: MEDLINE, PubMED, PsycINFO, and the Cochrane Central Register of Controlled Trials (January 1, 2013, to January 31, 2019 [children and adolescents]; January 1, 1992, to January 31, 2019 [young adults <25 years]); surveillance through March 20, 2020.
Study selection: Clinical trials of behavioral counseling interventions to prevent initiation of illicit and nonmedical drug use among young people.
Data extraction and synthesis: Critical appraisal was completed independently by 2 investigators. Data were extracted by 1 reviewer and checked by a second. Random-effects meta-analysis was used to estimate the effect sizes associated with the interventions.
Main outcomes and measures: Number of times illicit drugs were used; any illicit drug or any cannabis use.
Results: Twenty-nine trials (N = 18 353) met inclusion criteria. Health, social, or legal outcomes such as mental health symptoms, family functioning, consequences of drug use, and arrests were reported in 19 trials and most showed no group differences. The effects on illicit drug use in 26 trials among nonpregnant youth (n = 17 811) were highly variable; the pooled result did not show a clinically important or statistically significant association with illicit drug use (standardized mean difference, -0.08 [95% CI, -0.16 to 0.001]; 24 effects [from 23 studies]; n = 12 801; I2 = 57.0%). The percentage of participants using illicit drugs ranged from 2.3% to 38.6% in the control groups and 2.4% to 33.7% in the intervention groups at 3 to 32 months' follow-up. The median absolute risk difference between groups was -2.8%, favoring the intervention group (range, -11.5% to 14.8%). The remaining 3 trials provided a perinatal home-visiting intervention to pregnant Native American youth. One trial (n=322) found a reduction in illicit drug use at 38 months (eg, cannabis use in the previous month, 10.7% in the intervention group and 15.6% in the control group) but not at earlier follow-up assessments. Across all 29 trials, only 1 trial reported on harms and found no statistically significant group differences.
Conclusions and relevance: The evidence for behavioral counseling interventions to prevent initiation of illicit and nonmedical drug use among adolescents and young adults was inconsistent and imprecise, with some interventions associated with reduction in use and others associated with no benefit or increased use. Health, social, and legal outcomes were sparsely reported, and few showed improvements.