A Cochrane review [withdrawn from the Cochrane library] included 27 studies with a total of 3663 subjects. There was a wide heterogeneity in the interventions evaluated: this did not allow to provide a summary estimate of effect and results cannot be summarised in a clear cut way. The comparisons between different type of behavioural interventions showed results in favour of treatments with some form of contingency management in respect to both reducing drop outs and lowering cocaine use.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment) and by inconsistency (heterogeneity in interventions and outcomes).