Polydipsia literally means “excessive thirst” since the word is made up of “poly” meaning “many” and “dipsia” meaning “thirst”. Polydipsia is therefore a symptom of people who voluntarily drink large amounts of fluid, usually water.
The condition can be both physiological and psychological. When the cause is physiological, the person is stimulated to drink excessively as a result of hormone imbalances, fever, shock, or medication. Drugs which can cause this, include caffeine and diuretics.
One of the more common causes of polydipsia is diabetes insipidus. This condition, which is not be confused with diabetes mellitus (the insulin and glucose condition), occurs when the levels of a certain hormone, known as ADH or vasopressin, are excessively low, or when the kidneys are not able to respond normally to the hormone. As a result, large volumes of very dilute (or insipid) urine are produced, and the patient drinks excessively to replace the lost fluid.
Diabetes mellitus, when untreated, can also lead to polydipsia. In this case, glucose in the urine leads to large urine volumes. The patient again drinks excessively to replace the fluid that is lost.
When the cause is psychological, a condition known as psychogenic polydipsia exists, where patients with mental illnesses or developmental problems display an excessive desire to drink liquids.
If excessive thirst and drinking patterns are observed or noted, the obvious causes must first be eliminated – these include caffeine and other drugs, such as diuretics, which may stimulate excess urine output. In people with known diabetes (either insipidus or mellitus), treatment of the condition must take precedence, since the symptom will be treated as a matter of course.
Therefore, in patients who administer insulin, for example, blood glucose levels must be tightly controlled.
In all other patients with this symptom, medical advice should be sought. It is probably not advisable to refrain from drinking, since the thirst mechanism is an important regulator of body function and particularly of sodium concentration.
However, if the person falls within the subset of psychogenic disorders, they are not likely to recognise their own lack of thirst, and may drink to the point of being ill-health. In this situation, a second party should seek medical treatment, since the condition can be fatal.
When to see a doctor
When excessive thirst is persistent and cannot be attributed to acute fluid loss from exercise, or to the intake of caffeine or other medication, a doctor’s opinion should be sought. Again, if the problem is psychological, a second party should seek medical advice on behalf of the person who is suffering from the symptom.
What to expect at the doctor
The doctor will seek first to rule out diabetes mellitus and diabetes insipidus. This is done by means of a detailed questionnaire/history, and possibly tests to assess blood and urine glucose or ADH levels. A specialised test, known as a fluid deprivation test, is done to test for diabetes insipidus, as well as for the specific causes (ADH, kidneys, or voluntary excessive fluid intake).
In some cases, doctors may wish to examine for damage to the hypothalamus, which is responsible for regulating thirst through the hormone ADH.
Treatment depends on the specific cause of the symptom. In diabetics, treatment may include medication to control the glucose levels or to regulate ADH levels. If the cause is excessive caffeine or other diuretic substances, treatment may involve a change in medication (since they often contain these diuretics).