To assess the effectiveness of interventions directed at the prevention or reduction of use of illicit substances by young people or those directed at reducing harm caused by continuing use.

Databases searched for relevant studies include: MEDLINE, PsycLIT, Current Contents, ISDD database, ERIC, SciSearch, Social SciSearch, Health Periodicals Database, HEA Unicorn Database, Dissertation Abstracts, Aidsline and EMBASE. Key journals, references and citations of articles identified were also searched. Experts were contacted to identify grey or unpublished studies.

Study designs of evaluations included in the review

Studies with control group(s).

Specific interventions included in the review

School-based or targeted interventions that included psycho-educational prevention measures designed to prevent or delay onset of drug use, or leading to cessation of use, or minimise the harm associated with substance use.

Participants included in the review

Young people aged between 8 and 25 years.

Outcomes assessed in the review

Changes in drug using behaviour.

How were decisions on the relevance of primary studies made?

Decisions were made by reading the titles (and abstracts when available). Studies selected for inclusion in the final review was read by two or more reviewers, and any disagreements were resolved by discussion.

Included studies were categorised according to following methodological criteria: reported outcome of drug using behaviours, reported withdrawal or exclusion and possible impact on the findings, included comparisons of baseline data for different study conditions, corrected for any baseline differences identified. The authors do not state how the papers were assessed for validity, or how many of the reviewers performed the validity assessment.

The authors do not state how the data were extracted for the review, or how many of the reviewers performed the data extraction.

How were the studies combined?

The effect size was calculated using data reported in the individual studies: including means, standard deviations or frequencies and sample sizes; test of significance value and significance level (p value) and sample size. In meta-analysis of methodologically sound studies, studies were weighted by their sample size (N-3). Positive effect size indicated that drugs education was associated with less drug use. Fail-safe N was calculated to estimate how many additional studies with zero effect size was required to overturn the significant estimate in meta-analysis.

How were differences between studies investigated?

Chi-squared statistic was used to test heterogeneity in effect size across studies.

A total of 71 studies examining 62 separate evaluations of programmes met the inclusion criteria.

The majority of studies identified were evaluations of interventions introduced in schools and targeting alcohol, tobacco and marijuana simultaneously. These studies were methodologically stronger than interventions targeting other drugs and implemented outside schools.

Weighted mean effect size was 0.037 (p<0.002) for school-based interventions up to 1 year (11 studies) and 0.018 (p=0.016) for school-based studies lasting 2 years or longer (10 studies). Statistical test of heterogeneity was not significant (p=0.70 or p=0.99). Fail safe N was 944 for meta-analysis of studies with 1 year follow-up and 192 for meta-analysis of studies with >=2 year follow-up.

The impact of evaluated interventions was small with dissipation of programme gains over time. Interventions targeting hard to reach groups have not been evaluated adequately. Efforts need to be directed towards the development of improved evaluative solutions to the problems posed by these groups. There is still insufficient evidence to assess the effectiveness of the range of approaches to drugs education; more methodologically sound evaluations are required. There is also a need to target interventions to reflect the specific needs and experiences of recipients.

The review is methodological sound. The literature search was thorough. The quality of included studies was assessed. Outcome statistics reported in studies were used to estimate effect size, which enabled authors to quantitatively combine results of studies with different outcome measures. However, it is difficult to provide a clinically meaningful interpretation of observed effect sizes. In general, authors' conclusions are supported by the evidence presented in the review.

Practice: The authors stated that 'there is still insufficient evidence to assess the effectiveness of the range of approaches to drugs education; more methodologically sound evaluations are required'.

Research: The authors recommended that 'there is a need for the development of programmes that are individually paced to ensure that all participants receive the programme in full', and 'further research is required to determine the possible effects of booster sessions'.

Health Education Authority.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.