SIADH: What It Is, Why It Happens, and How to Treat It

If you’ve ever heard the term SIADH and felt confused, you’re not alone. SIADH stands for syndrome of inappropriate antidiuretic hormone. In plain language, it means your body is making too much of a hormone that tells the kidneys to hold onto water. The result? Blood sodium drops (hyponatremia) and you end up holding extra fluid.

Why Does SIADH Occur?

Several situations can trigger the over‑release of antidiuretic hormone (ADH). Common culprits include certain cancers (especially lung tumors), brain injuries, lung infections, and some medicines like antidepressants or chemotherapy drugs. Even severe pain or stress can push your body into this mode. The key point is that the body thinks it needs to save water, even when there’s already enough.

When ADH tells the kidneys to re‑absorb water, the kidneys reduce the amount of urine they make. This added water dilutes the sodium in your blood, leading to the hallmark low‑sodium level of SIADH. Low sodium can cause headache, nausea, confusion, and in severe cases, seizures or coma.

Spotting the Symptoms and Getting a Diagnosis

The symptoms of SIADH are often vague because they mimic many other conditions. You might feel unusually tired, have muscle cramps, or notice that you’re urinating less than usual. If you’re hospitalized for another reason and a blood test shows a sudden drop in sodium, doctors will start looking for SIADH.

Diagnosing SIADH involves a few steps:

• Blood tests that confirm low sodium and low plasma osmolality.
• Urine tests that show the kidneys are still concentrating urine (high urine osmolality) despite low blood sodium.
• Ruling out other reasons for hyponatremia, like heart failure, liver disease, or kidney problems.
• Imaging studies (CT or MRI) if a tumor or brain issue is suspected.

Once other causes are excluded, the diagnosis of SIADH becomes clearer.

How Is SIADH Treated?

Treatment focuses on three goals: stop the excess ADH, raise blood sodium safely, and address the underlying trigger.

First, doctors often limit fluid intake. Cutting down on water and other fluids reduces the dilution effect on sodium. In many cases, a fluid restriction of 800‑1000 ml per day is enough.

If fluid restriction isn’t enough, medications can help. Vaptans (like tolvaptan) block the action of ADH on the kidneys, letting the body get rid of excess water. Loop diuretics combined with salt tablets are another option, especially when rapid correction is needed.

In emergencies where sodium is dangerously low, a slow intravenous infusion of saline is used. Doctors are careful not to raise sodium too quickly because that can cause brain damage.

Finally, treating the root cause—whether it’s stopping a medication, removing a tumor, or managing a lung infection—often resolves SIADH on its own.

Living With SIADH

Most people recover once the underlying issue is fixed and fluid balance is restored. However, it’s wise to keep an eye on your fluid intake and watch for symptoms of low sodium. Regular follow‑up blood tests can catch any rebound problems early.

If you’re prescribed a medication that can cause SIADH, ask your doctor about warning signs and whether you need periodic monitoring. Small lifestyle tweaks—like a daily fluid log—can make a big difference.

In short, SIADH isn’t something you’ll catch on the street, but if you’re dealing with cancer, a brain injury, or certain meds, knowing the signs and treatment options can keep you from serious complications. Stay informed, talk to your healthcare team, and don’t ignore unusual fatigue or confusion—those could be clues your body is trying to tell you something.