Vasopressin, also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH), is a posterior pituitary hormone that is synthesised in the hypothalamus. Vasopressin is synthesised as a precursor protein that consists of arginine vasopressin and two associated proteins, neurophysin 2 and the glycopeptide copeptin. Vasopressin, together with its carrier protein neurophysin II, is packaged into neurosecretory vesicles and transported axonally to the nerve endings in the neurohypophysis, where it is either stored or secreted into the bloodstream. Vasopressin acts as a growth factor by enhancing pH regulation through acid-base transport systems. It has a direct antidiuretic action on the kidney and also causes vasoconstriction of the peripheral vessels. Vasopressin can also contract smooth muscle during parturition and lactation. It also plays a role in cognition, tolerance, adaptation and complex sexual and maternal behaviour, as well as in the regulation of water excretion and cardiovascular functions. Mutations in the vasopressin precursor cause autosomal dominant neurohypophyseal diabetes insipidus (ADNDI), which is characterised by persistant thirst, polydipsia and polyuria.