BACKGROUND: Many trials reported that brief interventions are effective in reducing excessive drinking. However, some trials have been criticised for being clinically unrepresentative and unable to inform clinical practice. OBJECTIVES: To assess the effectiveness of brief intervention, delivered in general practice or based primary care, to reduce alcohol consumption SEARCH STRATEGY: We searched the Cochrane Drug and Alcohol Group specialised register (February 2006), MEDLINE (1966 to February 2006), EMBASE (1980 to February 2006), CINAHL (1982 to February 2006), PsycINFO (1840 to February 2006), Science Citation Index (1970 to February 2006), Social Science Citation Index (1970 to February 2006), Alcohol and Alcohol Problems Science Database (1972 to 2003), reference lists of articles. SELECTION CRITERIA: Randomised controlled trials, patients presenting to primary care not specifically for alcohol treatment; brief intervention of up to four sessions. DATA COLLECTION AND ANALYSIS: Two authors independently abstracted data and assessed trial quality. Random effects meta-analyses, sub-group, sensitivity analyses, and meta-regression were conducted. MAIN RESULTS: The meta-analysis included 21 RCTs (7,286 participants), showing that participants receiving brief intervention reduced their alcohol consumption compared to the control group (mean difference: -41 grams/week, 95% CI: -57 to -25), although there was substantial heterogeneity between trials (I2 = 52%). Sub-group analysis (8 studies, 2307 participants) confirmed the benefit of brief intervention in men (mean difference: -57 grams/week, 95% CI: -89 to -25, I2 = 56%), but not in women (mean difference: -10 grams/week, 95% CI: -48 to 29, I2 = 45%). Meta-regression showed a non-significant trend of an increased reduction in alcohol consumption of 1.1, 95%CI: -0.05 to 2.2 grams/week, p=0.06, for each extra minute of treatment exposure, but no relationship between the reduction in alcohol consumption and the efficacy score of the trial. Extended intervention when compared with brief intervention was associated with a non-significantly greater reduction in alcohol consumption (mean difference = -28, 95%CI: -62 to 6 grams/week, I2 = 0%) AUTHORS' CONCLUSIONS: Brief interventions consistently produced reductions in alcohol consumption. When data were available by gender, the effect was clear in men at one year of follow up, but unproven in women. Longer duration of counselling probably has little additional effect. The lack of differences in outcomes between efficacy and effectiveness trials suggests that the current literature had clear relevance to routine primary care. Future trials should focus on women and on delineating the most effective components of interventions.