There are three major classes of drugs for the treatment of obesity: (i) inhibitors of food intake, which reduce hunger perception and, consequently, food intake; the most representative are centrally acting neurotransmitters and intestinal or neural satiety peptides; (ii) inhibitors of nutrient absorption, which reduce energy disposal through a peripheral gastrointestinal mechanism; and (iii) thermogenic drugs, which increase energy expenditure. At present, there are only two drugs for long-term use: sibutramine, an inhibitor of both serotonin and norepinephrine reuptake, and orlistat, a lipase inhibitor that targets pancreatic lipases and reduces absorption of dietary fat. New treatments and better drugs are expected in the near future because of the rapid expansion of research in body-weight regulation mechanisms.