Low levels of ADH may not be detectable on laboratory tests. In fact, some labs do not list a lower level of normal on their results. That said, people without the ability to produce ADH have a condition called central diabetes insipidus. In this condition, people cannot resorb water in the kidneys so they drink and urinate almost constantly. It is treated by administering ADH.

Some specific causes of low ADH are:

- Central diabetes insipidus

- Brain tumor

- Brain hemorrhage

- Primary polydipsia

The causes of high ADH levels are collectively known as syndrome of inappropriate antidiuretic hormone secretion or SIADH. In SIADH, the body cannot excrete sufficient amounts of water because ADH levels are chronically too high. As a result, sodium levels drop resulting in hyponatremia. If sodium levels drop slowly, there may be no or only subtle symptoms. If sodium levels drop rapidly, severe symptoms may occur, even death. Gradual hyponatremia causes slowed reaction times, cognitive slowness, and problems with balance and walking. Early symptoms of quickly dropping sodium include a lack of appetite, nausea, and malaise. This is followed by headache, muscle cramps, irritability, drowsiness, confusion, weakness, seizures, and coma. There are several causes of SIADH ranging from mental and neurological disorders, cancer, lung disease, genetic disorders and many medications.

Some specific causes of high ADH are:

- Stroke

- Psychosis

- Head trauma

- Brain tumor

- Surgery

- Lung tumor

- Porphyria

- Hereditary SIADH

- Old age

- Medications