Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Author: Marisa Healy, BSN, RN
Content Contributor: Allyson Distel, MPH
Last Reviewed: January 19, 2024

What is Syndrome of Inappropriate Antidiuretic Hormone (SIADH)?

Antidiuretic hormone (ADH) is a hormone made in your body. ADH is normally made in a part of the brain called the hypothalamus. When ADH is made somewhere other than the hypothalamus, it is called syndrome of inappropriate antidiuretic hormone (SIADH). ADH is made “inappropriately” (not how it should be) in the body.

The job of antidiuretic hormone, also called vasopressin, is to hold onto water in the body. ADH is made in the hypothalamus and stored and released by the pituitary gland. When your body is dehydrated (low on fluids), ADH is released, causing the body to hold on to water. Your body then makes less urine. When you urinate, it will be more concentrated (darker in color). 

In SIADH, the body holds on to too much water. As this extra fluid builds up, it makes your body think there is not enough sodium. Your body responds as if sodium levels are low. There is enough sodium in the body, but it is being diluted by the extra water. 

What causes SIADH?

Cancer is the most common cause of SIADH. Lung and head and neck cancers are the most common cancers that cause SIADH, among others. Other causes might be:

  • Meningitis.
  • Psychosis.
  • Lung disease.
  • Head trauma.
  • Some medications. 
  • Damage to the hypothalamus or pituitary gland.

What are the symptoms of SIADH?

Symptoms of SIADH look similar to when your body doesn’t have enough sodium (hyponatremia). Symptoms tend to be mild at first and are:

  • Cramps.
  • Muscle weakness.
  • Loss of appetite (not feeling hungry).
  • Irritability.
  • Nausea and vomiting.

The symptoms can become more serious if the SIADH is not treated. SIADH can lead to confusion, hallucinations, seizures, and even coma.

How is SIADH diagnosed?

To diagnose SIADH, your provider needs to review your symptoms and medications and look at your medical history. Urine and blood tests may be used to diagnose SIADH.

How is SIADH treated?

SIADH is treated in a few ways:

  • Treatment of underlying condition: If your SIADH is being caused by cancer, your cancer may be treated with surgery, chemotherapy, or radiation. Any other underlying conditions should also be treated.
  • Fluid Restriction: Your provider may limit the amount of fluid you take into your body through food and drinks. This will help prevent your body from retaining, or holding on to, fluid. Your provider will check for dehydration.
  • Medication: You may be prescribed a loop diuretic. A loop diuretic lowers the amount of fluid in your body by increasing the amount of urine you make. The more urine you make, the less fluid is in your body. Some electrolytes leave the body through the urine. As you urinate more, you may lose too many electrolytes. Your electrolyte levels can be checked with a blood test. 

When should I call my care team?

You should weigh yourself at least once each day. If you are gaining too much fluid weight, or notice new or worsening swelling, call your provider right away. Your care team will give you instructions for when to call your provider. If you have symptoms, such as weakness, confusion, cramps, irritability, nausea, and vomiting, call your care team right away. 

Vanhees SL, Paridaens R, Vansteenkiste JF. Syndrome of inappropriate antidiuretic hormone associated with chemotherapy-induced tumour lysis in small-cell lung cancer: case report and literature review. Ann Oncol 2000;11:1061–1065.

Yasir M, Mechanic OJ. Syndrome of Inappropriate Antidiuretic Hormone Secretion. [Updated 2023 Mar 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:

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