Genetic and pharmacological studies, involving both animals and humans, suggest that the central MC4 receptor plays a key role in homeostatic control, most probably via regulation of appetite and energy expenditure. This has stimulated intense research efforts in the field of drug discovery to identify MC4 receptor agonists and antagonists for the therapeutic treatment of obesity and diseases associated with loss of body weight. This article constitutes a near comprehensive review of the published scientific literature on small molecule ligands of the hMC4 receptor since 2002.