OBJECTIVES: Childhood obesity associates with significant morbidity and premature death; its prevalence has increased greatly during the past three decades; and it is recognized as a worldwide public health problem. However, the efficacy of treatments for childhood obesity remains unclear. In recent years the use of metformin, an insulin sensitizer, has aroused a great interest for the treatment of obesity in adults. Our aim was to assess the efficacy and safety of metformin for childhood obesity.METHODS: Systematic review of literature and meta-analysis of randomized controlled trials in obese subjects age ≤19 years without diabetes or other morbidities. Structured electronic searches of published studies until March 2010 were performed. Changes in the Body Mass Index (BMI) were considered our main outcome measure of efficacy whereas metabolic parameters such as insulin levels, glucose, HOMA, lipid profile and leptin levels were considered as secondary outcomes. Safety parameters included adverse events and losses from adverse effects. Individual studies were graded using published methodologies. Pooled estimates of effect and confidence intervals were derived using a fixed effects model and tested for heterogeneity. Consistency across studies was evaluated by means of the I-square statistic. RESULTS: Seven trials met the inclusion criteria. All trials compared metformin with placebo and used behavioural co-interventions. Average follow-up was six months. Though with small sample sizes, methodological quality of trials was adequate. Meta-analysis showed that compared to placebo, metformin provided a significant decrease in BMI (-1.90 (-3,-.8). No statistical significant differences were found in secondary outcomes. Main adverse effects were digestive, no serious adverse events were reported.CONCLUSIONS: Available evidence suggests that, added to behavioural interventions, metformin is a relatively safe and effective treatment for childhood obesity in the short term. Further research with longer follow-up periods is needed to solve this important health issue. Partially supported by Spanish National I+D Program