Finding out your sodium is low is often confusing, because most people worry about having too much salt, not too little. Low sodium — the medical term is hyponatremia — means the amount of sodium in your blood has dropped below normal. It has many possible causes, from common medications to drinking too much water, and treatment depends entirely on what is driving it.
What Does Low Sodium Actually Mean?
Sodium is an electrolyte. It helps carry electrical signals between cells and plays a central role in balancing the amount of water inside and outside your cells.
A normal blood sodium level is generally between 135 and 145 milliequivalents per liter (mEq/L). Below 135 mEq/L is considered low. Mild cases may cause no symptoms at all. More significant drops can cause confusion, headaches, nausea, or in serious cases seizures and coma.
Here is the part many people miss. Low sodium in the blood does not always mean your body has too little sodium overall. In many cases, your body has a normal amount of sodium but too much water, which dilutes it. That distinction matters because it changes how the problem is treated.
Why Would My Sodium Be Low? Common Causes
The most common causes of low sodium fall into a few broad groups. Doctors usually work through these systematically when the cause is not obvious.
Medications
Certain medications are among the most frequent culprits. Thiazide diuretics — a common class of blood pressure pills — are well known to lower sodium in some people. Antidepressants, particularly SSRIs and SNRIs, can also cause it. Carbamazepine, used for seizures and some pain conditions, is another. If you started a new medication and your sodium dropped, that timing is worth mentioning to your doctor.
Conditions That Affect Hormones and Kidney Function
Your body regulates sodium through a hormone called ADH (antidiuretic hormone), which controls how much water your kidneys hold onto. When ADH is too high, your body retains water and dilutes the sodium in your blood. Several conditions can cause this, including heart failure, liver cirrhosis, and a disorder called SIADH (syndrome of inappropriate antidiuretic hormone secretion). Underactive thyroid and adrenal insufficiency can also lower sodium.
Drinking Too Much Water
Drinking large amounts of water — especially during endurance exercise, or in some psychiatric conditions where people drink excessively — can dilute blood sodium faster than your kidneys can correct it. This is why some athletes are advised to include electrolytes during long events. It is not about the water being harmful. It is about the volume outpacing your body’s ability to balance it.
Other Causes
- Severe vomiting or diarrhea, which depletes sodium directly
- Diuretics that increase sodium loss through urine
- Certain cancers that trigger abnormal ADH release
- Low dietary sodium intake, though this is rarely the sole cause in healthy adults
- Recreational drugs such as MDMA, which can cause dangerous water retention
What Symptoms Should You Watch For?
Symptoms depend on how low the sodium is and how quickly it dropped. A slow decline over weeks may cause almost no symptoms until it becomes severe. A rapid drop can cause serious problems quickly.
Mild symptoms include fatigue, headache, nausea, and difficulty concentrating. Moderate symptoms include confusion, muscle weakness, and unsteadiness. Severe hyponatremia can cause seizures, loss of consciousness, and in rare cases brain swelling, which is a medical emergency.
If you or someone else has confusion, seizures, or loss of consciousness along with a known or suspected low sodium level, seek emergency care immediately. Do not wait to see if it improves on its own.
How Is Low Sodium Diagnosed?
A basic blood test called a basic metabolic panel or comprehensive metabolic panel measures sodium. If your level is below 135 mEq/L, your doctor will typically order additional tests to find the cause.
These may include urine sodium and urine osmolality tests, thyroid function tests, adrenal function tests, and sometimes imaging. The goal is to determine whether your body is losing sodium, retaining water, or both — because the treatment differs depending on the answer.
Your doctor will also review your medications and ask about your fluid intake. This history is often as informative as the lab work.
How Is Low Sodium Treated?
Treatment depends on the cause, how low the sodium is, and whether symptoms are present. There is no single approach.
Mild, Chronic Low Sodium
If sodium is mildly low and there are no symptoms, treatment often focuses on the underlying cause. That might mean adjusting or switching a medication, treating an underlying condition, or in some cases limiting fluid intake. Some clinicians recommend increasing dietary sodium, but this is not appropriate for everyone and should be discussed with a doctor.
Moderate to Severe Low Sodium
When sodium is significantly low or causing symptoms, treatment may involve intravenous fluids or medications. In some cases, a medication called a vasopressin receptor antagonist (often called a vaptan) is used to help the body excrete excess water. This is a specialized treatment used under close medical supervision.
One important caution: sodium levels must be corrected slowly. Raising blood sodium too quickly can cause a serious and sometimes permanent neurological condition called osmotic demyelination syndrome. This is why severe hyponatremia is treated in a hospital setting with careful monitoring.
What You Should Not Do
Do not try to fix low sodium on your own by eating large amounts of salt or taking salt tablets. This can be dangerous, especially if the cause is water retention rather than sodium loss. The wrong treatment can make the problem worse.
Can Low Sodium Be Prevented?
Not all cases can be prevented, especially those caused by medications or underlying illness. But some steps may reduce risk in certain situations.
- If you take a thiazide diuretic, ask your doctor whether your sodium should be checked periodically, especially in the first few weeks of treatment
- During endurance events, replace both fluids and electrolytes rather than drinking water alone in large amounts
- If you have heart, liver, or kidney disease, follow your care team’s guidance on fluid intake
- Report new symptoms like confusion or unusual weakness to your doctor, especially if you recently started a new medication
What the Evidence Shows — and What It Does Not
The link between thiazide diuretics and hyponatremia is well established in clinical literature. The role of ADH in water retention and dilutional hyponatremia is also well understood. What is less clear is how aggressively to treat mild, chronic hyponatremia in people without symptoms. Some research suggests that even mild, long-standing low sodium may affect thinking and balance, but the evidence on whether treating it improves those outcomes is mixed.
Be cautious of anyone selling supplements or products claiming to “fix” low sodium. No supplement has been shown to reliably correct hyponatremia, and self-treating can be harmful.
Frequently Asked Questions
Can low sodium be caused by drinking too much water?
Yes. Drinking large amounts of water, especially during endurance exercise, can dilute the sodium in your blood faster than your kidneys can correct it. This is called exercise-associated hyponatremia and can be serious.
Is low sodium always caused by not eating enough salt?
No. In most cases, low blood sodium is caused by too much water in the body rather than too little sodium in your diet. That is why treatment often focuses on fluid balance, not just adding salt.
Can low sodium be dangerous?
Yes, if it develops quickly or drops very low. Severe hyponatremia can cause seizures, loss of consciousness, and brain swelling. Mild cases often cause no symptoms but still need medical evaluation.
Should I take salt tablets for low sodium?
No, not without medical guidance. Taking salt tablets on your own can be dangerous, especially if the cause is water retention rather than sodium loss. Your doctor can determine the right treatment based on the cause.
