What does diabetes insipidus primarily cause?

Diabetes insipidus is characterized primarily by the body's inability to regulate fluid balance, resulting from a deficiency of the hormone vasopressin (also known as antidiuretic hormone, or ADH) or from the kidneys' inability to respond to this hormone. The lack of vasopressin or the ineffective response leads to an inability to concentrate urine, which causes large volumes of dilute urine to be produced. This excessive urination is known as polyuria, and because of the loss of significant amounts of water, individuals often experience excessive thirst, referred to as polydipsia. This combination of symptoms—excessive thirst and increased urination—defines diabetes insipidus and is what makes it distinct from other forms of diabetes, such as diabetes mellitus, which involves issues related to blood glucose levels.