Either a total or partial lack of the hormone vasopressin can cause diabetes insipidus. This is a condition in which the kidneys are not able to retain water, causing a person to urinate frequently resulting in excessive thirst which causes patients to drink enormous amounts of water.

If vasopressin replacement is not done, a person will pass large amounts of dilute urine and be very thirsty and drink massive amounts of water. Eventually, the person becomes dehydrated, loses consciousness and can die.
Vasopressin replacement is usually done by giving desmopressin, a synthetic version of vasopressin in a nose spray or a tablet. It lasts 12 to 24 hours.

Because individuals vary widely, it is necessary to measure how long a specific dose will be effective. By measuring the amount of urine voided and how diluted it is, the proper dosage can be identified. . If the water loss is mild,. and does not interfere with sleep, patients can be encouraged to drink until their thirst resolves and may require no treatment

If too much vasopressin is administered, patients develop a low blood salt, which can result in headache, nausea, vomiting, confusion and unconsciousness. If too little vasopressin is administered, patients pass very large volumes of urine, become thirsty and drink excessive amounts of water, resulting in sever dehydration and increase in blood salt.