Neuromedin U (NmU) is a neuropeptide expressed in various organs including the brain, gut, bone marrow and lungs. NmU has a wide range of roles in physiology including: decreasing appetite and body weight and increasing gross locomotor activity, heat production, oxygen consumption, uterine smooth muscle contraction, body temperature, and bone mass. It is also involved in regulating circadian rhythm, stress response and blood flow and ion transport in the gut. NmU can also stimulate cytokine production and promote mast cell-mediated inflammation and is important during the early proliferative stages of erythroid development. NmU has been shown to be a c-Myb target gene and NmU in turn activates protein kinase C-βII, a factor associated with hematopoietic differentiation-proliferation.

Two related G protein–coupled receptors have been identified as NmU receptors: NMU-R1: expressed in various tissues, including the small intestine and lung, and NMU-R2: predominantly expressed in the hypothalamus and the small intestine. Activation of these receptors via NmU binding mobilises intracellular Ca2+ stores and downstream signalling.