Diabetes insipidus is a condition caused by an abnormality of the
pituitary gland which leads to a defi ciency of the hormone vasopressin.
When a person has diabetes insipidus, this affects the body’s ability to
control the level of fl uid in the blood and urine. As a result, there is no
stimulus for fl uid to be retained in the body and so it is lost in the urine
which becomes very dilute and is passed in large quantities. Due to the
excessive urine loss, a person with diabetes insipidus will usually feel
very thirsty.