Fifteen studies (n=1,928) reported in 18 articles were included. Thirteen of these were randomised controlled trials.
The quality of the studies was high (mean score 12.0, range: 8 to 15). Inter-rater agreement was 0.96 for the data extraction and coding and 95% for the validity assessment.
Many treatments reduced substance abuse and increased abstinence. The ES ranged from 0.51 for coping skills training to -1.25 for behavioural therapy. Benefits found immediately after treatment were often not sustained at follow-up, with ESs ranging from 0.39 for cognitive-behavioural therapy to -0.87 and -0.86 for cognitive-behavioural therapy and multidimensional family therapy, respectively.
The interventions were graded as follows.
ES>0.20 with at last 1 year' follow-up or replication and using strong study design: multidimensional family therapy and cognitive-behavioural group treatment.
ES>0.20 with relatively strong study designs and less than 1 year' follow-up and no replication: behavioural therapy, multisystemic therapy, combined cognitive-behavioural therapy and functional family therapy, family systems therapy, functional family therapy, combined Botvin life-skills with additive programmes, and psychoeducational therapy.
Negligible or unwanted effect with less strong study design: supportive group counselling, interactional group treatment, aftercare services and residential treatment services.
Negligible or unwanted effect with relatively strong study design: support for individual counselling, family education, adolescent group treatment and individual cognitive-behavioural treatment.