Significance: Obesity is a multifactorial disease with many risks to public health, with 39.6% of American adults and 18.5% of young people obese. Brazil ranks fifth in the world rankings, with about 18 million people. In this scenario, melatonin has evidenced an important function in the regulation of energy metabolism. Information gap: What is the real influence of melatonin supplementation on obesity and T2DM control? Objective: A systematic review of the physiological and endocrine aspects of melatonin was performed, as well as to analyze the real impact of its use for the treatment of obesity and type 2 diabetes in humans. Methods: 51 studies were selected to make up the textual part of the manuscript and 44 to make the Meta-analysis. The PRISMA rules followed. Results and Conclusion: Many studies have shown the importance of melatonin in various diseases, especially obesity, T2DM and metabolic syndrome. Human studies have shown that the use of melatonin is simple, safe, and has no side effects. Nevertheless, intervention studies using this hormone in obese or diabetic patients do not yet have a consensus on supplementation.

Keywords: Melatonin. Obesity. Metabolism. Type 2 diabetes. Clinical study.