Background: The Cochrane Drugs and Alcohol Group, founded in 1998, aims to produce, update and disseminate systematic reviews on the prevention, treatment and rehabilitation of problematic use of drugs and alcohol. Objectives: To review the state of the art of Cochrane systematic reviews in the area of drug and alcohol in terms of available evidence. Methods: Reviews published by the group are investigated. Results: By February 2008, the Group published 44 reviews and 15 protocols. A total of 598 studies were included, out of 1651 trials considered for inclusion (36%). The main reasons for exclusion were study design (42%) and type of intervention (28%). Ninety-one per cent of studies included were found in electronic databases. About 41% were published in 9 specialised journals, the remaining studies were published in 168 different journals. Eighty-eight per cent of the included studies were randomised controlled trials, 16% of them reported adequate allocation concealment. The areas where studies were conducted are North America (68%), Europe (23%), Australia/New Zealand (5%), Asia (4%), South Africa (1%) and the Middle East (0.5%). The interventions proved to be beneficial or likely to be beneficial varied according to the substance considered: 22% for alcohol, 50% for opiate, 12% for cocaine, 10% for prevention and none for cannabis and amphetamines. In 79% of the published reviews, it is possible to find specific suggestions for future primary research. Conclusions: Cochrane systematic reviews do provide information on the most effective treatments, particularly in the area of opioid dependence. However, some major weaknesses in the available primary studies should e underlined. Even though several trials have been published in the field of addiction, only a few could be incorporated in the systematic reviews. A serious threat to internal validity in published trials is the absence of description of allocation concealment; a great majority of trials have been conducted in the US. A big effort should be put to facilitate the conduct of high quality multi-site randomized studies in the area where more uncertainties about effectiveness of interventions is present. A better linkage between the process of conducting systematic reviews and priority setting for primary research is foreseen.