SIADH: Why Is My Body Holding Too Much Water?

It’s a feeling many of my patients describe – just not being quite right. Maybe you’ve noticed you’re more tired than usual, perhaps a bit fuzzy-headed, or your muscles feel weak and crampy. Sometimes, these vague feelings can be a sign that your body’s water and salt balance is off, and one condition we look into is something called SIADH, or the Syndrome of Inappropriate Antidiuretic Hormone Secretion. It sounds like a mouthful, I know! But understanding it is the first step.

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So, What Exactly Is SIADH, Doc?

Alright, let’s break this down. Your body has a clever little hormone called antidiuretic hormone (ADH), which also goes by the name vasopressin. Think of ADH as a water manager. It’s made in a part of your brain called the hypothalamus and then stored and released by another tiny gland, the posterior pituitary.

Its main job? To tell your kidneys how much water to hang onto.

Normally, if you’re getting a bit dehydrated, your body releases more ADH. This signals your kidneys to reabsorb more water, so you pee less and keep more fluid inside. Smart, right?
And if you’ve had plenty to drink, ADH levels drop, and your kidneys let go of more water.

Now, with SIADH, this system goes a bit haywire. Your body makes too much ADH, or ADH works overtime when it shouldn’t. This means your kidneys hold onto too much water. All that extra water dilutes your blood, and a key thing that gets diluted is sodium (salt). This leads to a condition called hyponatremia, which simply means low sodium levels in your blood. And that’s often what causes the symptoms you might feel.

I see SIADH more often in folks who are in the hospital, especially after surgery. The stress of surgery, fluids they receive, and some pain medications can sometimes trigger it. It also tends to be more common as we get older.

What Might You Notice with SIADH?

Because your body is holding onto extra water, your urine often becomes very concentrated – less water, more waste. The main issues, though, usually stem from that low sodium, the hyponatremia.

If your sodium level is just a little low, you might not feel anything at all. But as it drops further, you could experience:

Muscle cramps or a feeling of weakness
Nausea, maybe even vomiting
A persistent headache
Feeling unsteady on your feet, which can sometimes lead to falls
Changes in your thinking – like confusion, memory blips, or just not acting like yourself
In really severe cases, things like seizures or even a coma can happen. This is serious, and why we take it very seriously.

Why Does SIADH Happen?

It’s not usually something that just pops up on its own. Most often, SIADH is a consequence of something else going on in the body. There’s a very rare hereditary type, called nephrogenic SIADH, linked to a gene change, but that’s not common.

More frequently, we see SIADH linked to:

Certain Cancers: Some tumors, especially small-cell lung cancer (SCLC), can actually start producing their own ADH. It’s less common, but other cancers like head and neck cancers or olfactory neuroblastomas (a rare nasal cavity cancer) can also be culprits.
Brain and Nervous System Issues: Anything affecting your central nervous system – your brain and spinal cord – can throw off ADH. This includes things like a stroke, bleeding in the brain (hemorrhage), infections, head injuries, and, rarely, severe mental health conditions (psychosis).
Medications: A surprising number of common medications can sometimes cause SIADH. These can include certain drugs for seizures, depression, cancer, and even some for heart conditions, diabetes, or blood pressure. It’s always a good idea for us to review your medication list if we suspect SIADH.
Surgery: As I mentioned, operations, especially those under general anesthesia, can sometimes lead to temporary SIADH. Your body’s response to the stress of it all.
Lung Diseases: Things like pneumonia (whether it’s viral, bacterial, or from tuberculosis) can sometimes trigger SIADH. We’re still figuring out the exact “why” on that one.
Hormone Imbalances: Less commonly, conditions like hypopituitarism (when the pituitary gland doesn’t make enough hormones) or an underactive thyroid (hypothyroidism) can play a role.

Figuring Out If It’s SIADH

If you come to me with symptoms that make me think about your sodium levels, the first thing I’ll do is a thorough check-up and talk with you about how you’re feeling. Understanding your fluid status – whether you seem dehydrated, overloaded with fluid, or just right – is really important.

There isn’t one single “aha!” test for SIADH. We can measure ADH levels in the blood, but those results can take a while to come back. So, we usually start by looking for that hyponatremia and trying to understand why it’s happening. This often involves:

A Comprehensive Metabolic Panel (CMP): This is a common blood test that checks your kidney function, electrolytes (like sodium), and more.
An Osmolality blood test: This measures the concentration of particles in your blood.
A Urine osmolality test: Similarly, this checks the concentration of your urine.
Urine sodium and potassium tests: These help us see how much salt your kidneys are getting rid of.
Sometimes, toxicology screens if we think a medication might be involved.

If it’s a child we’re concerned about, we might also consider imaging tests of their lungs or brain, depending on the situation.

How We Can Help Manage SIADH

The good news is, we have ways to manage SIADH. The approach really depends on what’s causing it.

Treating the Underlying Cause: If there’s something specific triggering it, like a medication, we might adjust the dose or try a different one. If it’s an infection, we’ll treat that. If a tumor is producing ADH, treatment might involve surgery, chemotherapy, or radiation, depending on the type and stage.
Fluid Restriction: This is a cornerstone of managing SIADH. It sounds simple, but carefully limiting how much fluid you drink each day helps prevent your body from holding onto too much excess water. We’ll figure out a specific daily limit for you – and that includes everything: water, coffee, tea, juice, soda, you name it.
For Severe Symptoms: If hyponatremia is severe and causing serious symptoms like confusion or seizures, that’s an emergency. In the hospital, we can give a concentrated salt solution through an IV very carefully to bring sodium levels up safely.
Medications: In some cases, we might use medications that block ADH’s effect on the kidneys. This helps your kidneys release more water in your urine.

We’ll discuss all the options and decide on the best plan for you. It’s a team effort.

Key Things to Remember About SIADH

SIADH means your body makes too much antidiuretic hormone (ADH), causing it to hold onto too much water.
This extra water dilutes your blood sodium, leading to hyponatremia, which causes most symptoms.
Symptoms can range from mild (muscle cramps, nausea) to severe (confusion, seizures).
Many things can cause SIADH, including some cancers, brain issues, medications, and lung diseases.
Diagnosis involves blood and urine tests to check sodium and concentration levels.
Treatment focuses on limiting fluids, addressing the underlying cause, and sometimes medications.

You’re Not Alone in This

Hearing a diagnosis like SIADH can be worrying, I completely understand. But the outlook often depends on what’s causing it, and many of those causes are treatable. If your sodium levels drop very quickly (acute hyponatremia), that’s generally more serious than if it develops slowly over time (chronic hyponatremia). Chronic low sodium can sometimes lead to issues like poor balance or memory problems, which is why we want to get it sorted.

If you’re ever experiencing symptoms like muscle cramps, new problems with balance, or just feeling “off,” please do reach out. And if you or someone you know shows signs of severe hyponatremia like sudden confusion, hallucinations, or seizures, that’s a time to get to the nearest hospital right away. We’re here to help figure things out.