Setmelanotide (IMCIVREE™, Rhythm Pharmaceuticals) is a melanocortin-4 (MC4) receptor agonist developed for the treatment of obesity arising from proopiomelanocortin (POMC), proprotein convertase subtilisin/kexin type 1 (PCSK1), or leptin receptor (LEPR) deficiency. The drug has received its first approval in the USA for chronic weight management in patients 6 years and older with obesity caused by POMC, PCSK1 and LEPR deficiency and has been granted PRIority MEdicines (PRIME) designation by the European Medicines Agency for the treatment of obesity and the control of hunger associated with deficiency disorders of the MC4 receptor pathway. Setmelanotide is also being developed in other rare genetic disorders associated with obesity including Bardet–Biedl Syndrome, Alström Syndrome, POMC and other MC4R pathway heterozygous deficiency obesities, and POMC epigenetic disorders. This article summarizes the milestones in the development of setmelanotide leading to this first approval for obesity caused by POMC, PCSK1 and LEPR deficiency.