Diabetes insipidus is a condition that causes excess urine production and persistent thirst. Syndrome of inappropriate antidiuretic hormone (SIADH) causes your body to retain too much water.

Diabetes insipidus is thought to affect about 1 in 25,000 people worldwide. Most people make 1–3 quarts of urine a day, but some people with diabetes insipidus can make up to 20 quarts per day.

Diabetes insipidus is usually caused by underproduction of a hormone called vasopressin, but it can also develop if your kidneys aren’t properly responding to this hormone.

People with SIADH have the opposite problem. They produce too much vasopressin and retain too many fluids. It can develop due to difficulties with your pituitary gland or from excessive vasopressin produced from other sources such as cancer cells.

Read on to learn more about these two conditions that cause difficulties with your water balance.

How is ADH involved in SIADH and diabetes insipidus?

Vasopressin, also called antidiuretic hormone (ADH), is produced by your hypothalamus and secreted by your posterior pituitary gland. Its main function is to tell your kidneys to retain more water.

Issues with vasopressin can lead to difficulties with your fluid balance or electrolyte levels.

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Diabetes insipidus and SIADH cause opposite problems. People with diabetes insipidus pass too much water, whereas people with SIADH retain too much. Both conditions can lead to complications.

Diabetes insipidus symptoms

The main symptoms of diabetes insipidus are:

Frequently needing to pee may disrupt your sleep and cause additional symptoms, such as:

SIADH symptoms

SIADH causes your body to retain too much fluid, which can lead to a condition called hyponatremia. Hyponatremia is when your sodium levels are too low. It causes complications such as:

In severe cases it can cause:

Diabetes insipidus causes

Diabetes insipidus can develop for one of four reasons.

SIADH causes

SIADH usually develops as a complication of other medical conditions. Potential causes include:

  • conditions affecting your brain such as:
  • cancer, especially small cell lung cancer
  • medications such as:
    • carbamazepine (Tegretol)
    • oxcarbazepine (Trileptal, Oxtellar XR)
    • chlorpropamide
  • surgery, possible due to stimulation of pain sensors
  • lung disease, particularly pneumonia
  • low thyroid hormone levels or low pituitary hormones
  • administration of vasopressin, desmopressin, or oxytocin to treat other medical conditions
  • HIV infection
  • genetic factors

SAIDH and diabetes insipidus both cause problems with water balance. Some of the underlying causes can be the same. For example, they can both be caused by brain tumors or genetic factors.

Both can also cause imbalances in electrolyte levels. Electrolytes are minerals dissolved into your bodily fluids. Disruptions to your electrolyte levels can cause many problems throughout your body, such as:

  • fatigue
  • seizures
  • mood changes
  • cognitive changes
  • muscle weakness

Diabetes insipidus and SIADH can be treated with medications to regulate your vasopressin levels and other treatments to help regulate your water balance. You may need additional treatments depending on your underlying cause.

If you have SIADH, your doctor might tell you to restrict your water intake to less than 800 milliliters per day. You may need oral sodium tablets or sodium administered through an intravenous (IV) injection.

A group of medications called vasopressin receptor antagonists can help counteract the effect of vasopressin in your body.

Diabetes insipidus can be treated with a synthetic version of vasopressin called desmopressin. This artificial hormone can be administered:

  • by mouth
  • through you nose
  • by injections through your skin
  • through an IV

Gestational diabetes insipidus usually doesn’t require treatment.

Diabetes insipidus isn’t the same as the more common diabetes mellitus, where levels of glucose in the blood are chronically high.

It’s possible to have both types of diabetes at the same time, although it’s rare. Researchers reported a case of a 72-year-old man with evidence of both in a 2018 case study.

It’s possible to develop both diabetes insipidus and SIADH, although it’s rare.

In 2022 research, the study authors reported a case of a 49-year-old Japanese man who developed SIADH followed by central diabetes insipidus as complications of a pituitary tumor.

SIADH and diabetes insipidus are two conditions that cause problems with your fluid balance. People with diabetes insipidus urinate more frequently than normal and develop excessive thirst.

SIADH causes the opposite problem. People with this condition retain too much water, which can lead to problems such as low salt levels.

Both conditions are potentially treatable with medications and other treatments for the underlying causes.