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What is SIADH?
To function properly, every cell in our bodies needs to a certain level of salt. When the salt balance in the body is disturbed, many things can start going wrong.
Antidiuretic hormone (ADH), also known as vasopressin, controls the way your body retains or secretes water. ADH causes the body to retain water, which lowers the salt concentration throughout the body. The syndrome of inappropriate secretion of antidiuretic hormone, SIADH for short, occurs when your body makes too much ADH.
SIADH is the most common cause of low body salt (known as hyponatraemia). 
SIADH can be the result of numerous different disorders, including, but not limited to:
Brain and nerve disorders:
- Meningitis and encephalitis;
- Brain abscess;
- Head injury;
- Guillain-Barre syndrome;
- Hypothalamus or pituitary gland disorders;
- Multiple sclerosis;
- Shy-Drager syndrome;
- Delirium tremens ('the shakes'), and;
- Brain cancer;
- Lung cancer, especially small cell carcinoma;
- Other small cell carcinomas;
- Oesophageal cancer;
- Nasopharyngeal cancer;
- Prostate cancer, bladder cancer, endometrial cancer;
- Pancreatic cancer, and;
- Bowel cancer.
SIADH can be a side effect of certain medications and substances, such as:
- Hormone treatments (vasopressin, oxytocin);
- Antipsychotic drugs;
- Cyclophosphoamide, and;
- MDMA ('ecstasy').
Signs and symptoms
- Nausea, vomiting;
- Loss of appetite;
- Stomach aches;
- Confusion, hallucinations, irritability and personality changes;
- Unsteady balance and increased chance of falls;
- Muscle cramps, and;
- Seizures, coma.
Many people with mild SIADH often have no symptoms, or their symptoms may not be recognised as SIADH symptoms. This is especially common in elderly people, where reduced mental abilities - for example, poor concentration or forgetfulness - are often blamed on age or other causes  .
Methods for diagnosis
Your doctor will suspect SIADH if you display symptoms and have a medical condition or history that would put you at risk of SIADH. To confirm the diagnosis and rule out other conditions, urine tests and blood tests will be done to check your salt levels.
Types of treatment
Treatment of SIADH can take several forms:
- A high-salt infusion can be used to treat acute cases of SIADH in the short term;
- SIADH can be cured if the underlying medical condition or cause is treated. For instance, if SIADH is the side effect of a particular medication, adjusting the dose or using an alternative medication often helps reverse SIADH;
- If the underlying cause is not treatable, it is often best to treat SIADH with fluid restriction, which is limiting the amount of water a person drinks. Your doctor will advise you how to safely do this;
- Treatment with diuretic medication, such as frusemide, can encourage the body to get rid of excess water, and;
- Medications called 'vaptans', or vasopressin-receptor antagonists, have recently begun to be used to treat SIADH. Vaptans limit ADH activity; however, these medications are not widely available. 
If not treated, SIADH can lead to very low salt concentrations, which can interfere with the function of many of the body's systems, and is associated with a significant rise in illness and death rates  .