Hyponatremia

Date Updated: 07/18/2025

Overview

Hyponatremia is a condition that happens when the level of sodium in the blood is lower than the typical range. Sodium is an electrolyte, and it helps regulate the amount of water that's in and around your cells.

In hyponatremia, one or more factors cause the sodium in the body to be diluted. These factors can range from an underlying medical condition to drinking too much water. When this happens, the body's water levels rise, and cells begin to swell. This swelling can cause many health problems, from mild to life-threatening.

Hyponatremia treatment is aimed at resolving the underlying condition. Depending on the cause of hyponatremia, you may simply need to cut back on how much you drink. In other cases of hyponatremia, you may need intravenous electrolyte solutions and medications.

Symptoms

Hyponatremia signs and symptoms may include:

Nausea and vomiting.
Headache.
Confusion.
Loss of energy, drowsiness and fatigue.
Restlessness and irritability.
Muscle weakness, spasms or cramps.
Seizures.
Coma.

When to see a doctor

Seek emergency care for anyone who develops serious signs and symptoms of hyponatremia, such as nausea and vomiting, confusion, seizures, or lost consciousness.

Call your healthcare professional if you know you are at risk of hyponatremia and are experiencing nausea, headaches, cramping or weakness. Depending on the extent and duration of these symptoms, your healthcare professional may recommend seeking immediate medical care.

Causes

Sodium plays a key role in your body. It helps maintain normal blood pressure, supports the work of your nerves and muscles, and regulates your body's fluid balance.

A healthy blood sodium level is between 135 and 145 millimoles per liter (mmol/L). Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.

Many possible conditions and lifestyle factors can lead to hyponatremia, including:

Certain medicines. Some medicines can interfere with the hormonal and kidney processes that keep sodium concentrations within the healthy range. Water pills called diuretics, antidepressants and pain medicines can all affect sodium levels in your body.
Heart, kidney and liver problems. Congestive heart failure and certain diseases affecting the kidneys or liver can cause fluids to collect in your body. When this happens, it dilutes the sodium, lowering the overall level.
Syndrome of inappropriate anti-diuretic hormone (SIADH). In this condition, high levels of the anti-diuretic hormone (ADH) are produced, causing your body to retain water instead of excreting it in your urine. ADH is also known as vasopressin hormone.
Chronic, severe vomiting or diarrhea and other causes of dehydration. This causes your body to lose electrolytes, such as sodium, and also increases ADH levels.
Drinking too much water. Drinking excessive amounts of water can cause low sodium by overwhelming the kidneys' ability to excrete water. Because you lose sodium through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can also dilute the sodium content of your blood.
Hormonal changes. Adrenal gland insufficiency, known as Addison's disease, affects your adrenal glands' ability to produce hormones that help maintain your body's balance of sodium, potassium and water. Low levels of thyroid hormone also can cause a low blood-sodium level.
The recreational drug ecstasy. This amphetamine increases the risk of severe and even fatal cases of hyponatremia.

Risk factors

The following factors may increase your risk of hyponatremia:

Age. Older adults may have more contributing factors for hyponatremia. Those factors include age-related changes, taking certain medicines and a greater likelihood of developing a chronic disease that alters the body's sodium balance.
Certain drugs. Medications that increase your risk of hyponatremia include thiazide diuretics as well as some antidepressants and pain medicines. In addition, the recreational drug ecstasy has been linked to fatal cases of hyponatremia.
Conditions that decrease your body's water excretion. Medical conditions that may increase your risk of hyponatremia include kidney disease, heart disease, and syndrome of inappropriate anti-diuretic hormone (SIADH), among others.
Intensive physical activities. People who drink too much water while taking part in marathons, ultramarathons, triathlons and other long-distance, high-intensity activities are at an increased risk of hyponatremia.

Complications

In chronic hyponatremia, sodium levels drop gradually over 48 hours or longer — and symptoms and complications are typically more moderate.

In acute hyponatremia, sodium levels drop rapidly. This results in potentially dangerous effects, such as rapid brain swelling, which can result in a coma and death.

People who are premenopausal appear to be at the greatest risk of hyponatremia-related brain damage. This may be related to the effect of sex hormones on the body's ability to balance sodium levels.

Prevention

The following measures may help you prevent hyponatremia:

Treat associated conditions. Getting treatment for conditions that contribute to hyponatremia, such as adrenal gland insufficiency, can help prevent low blood sodium.
Educate yourself. If you have a medical condition that increases your risk of hyponatremia or you take diuretic medicines, be aware of the symptoms of low blood sodium. Always talk with your healthcare professional about the risks of a new medication.
Take precautions during high-intensity activities. Athletes should drink only as much fluid as they lose due to sweating during a race. Thirst is generally a good guide to how much water or other fluids you need.
Consider drinking sports beverages during demanding activities. Ask your healthcare professional about replacing water with sports beverages that contain electrolytes when participating in endurance events such as marathons or triathlons.
Drink water in moderation. Drinking water is vital for your health, so make sure you drink enough fluids. But don't overdo it. Thirst and the color of your urine are often the best indications of how much water you need. If you're not thirsty and your urine is pale yellow, you are likely getting enough water.

Diagnosis

Low sodium levels in the blood can be caused by many factors. Your healthcare professional will start by asking about your medical history and doing a physical examination. This may include questions about the medicines you take.

However, because the symptoms of hyponatremia occur in many conditions, it's impossible to diagnose the condition based on a physical exam alone. To confirm low blood sodium, your healthcare team may order blood tests and urine tests.

Treatment

Hyponatremia treatment is aimed at addressing the underlying cause, if possible.

If you have moderate, chronic hyponatremia due to your diet, diuretics or drinking too much water, your healthcare professional may recommend temporarily cutting back on fluids. They also may suggest adjusting your diuretic use to increase the level of sodium in your blood.

If you have serious, acute hyponatremia, you'll need more aggressive treatment. Options include:

Intravenous fluids. Your healthcare professional may recommend an IV sodium solution to slowly raise the sodium levels in your blood. This requires a stay in the hospital for frequent monitoring of sodium levels as too rapid of a correction is dangerous.
Medicines. You may take medicines to manage the signs and symptoms of hyponatremia, such as headaches, nausea and seizures.

Preparing for an appointment

Seek emergency care for anyone who develops serious symptoms of hyponatremia, such as nausea and vomiting, confusion, seizures, or lost consciousness.

Call your healthcare professional if you know you are at risk of hyponatremia and are experiencing nausea, headaches, cramping or weakness. Depending on the extent and duration of these signs and symptoms, your healthcare professional may recommend seeking immediate medical care.

Here's some information to help you get ready for your appointment, and what to expect from your healthcare team.

What you can do

List any symptoms you or your loved one has been experiencing and for how long.
Write down key medical information, including other medical problems for which you are being treated. Include the names of all medications, vitamins, supplements or other natural remedies you are taking.
Take a family member or friend along, if you are the one with symptoms of low blood sodium. Someone who accompanies you can help remember all of the information and provide support if you need immediate medical care.
Write down questions to ask your healthcare professional.

For hyponatremia, some basic questions to ask your healthcare professional include:

What's the most likely cause of my symptoms?
What causes hyponatremia?
How serious is the condition?
What treatment do you recommend?
How soon do you expect my symptoms will begin to improve?
Am I at risk of any long-term problems?
How can I prevent a recurrence of this condition?
Do I need to make any changes to how much fluid I usually drink?

What to expect from your doctor

Being ready to answer your healthcare team's questions may reserve time to go over any points you want to talk about in-depth. Your team may ask:

What are your symptoms and when did they start?
Have you started taking any new medicines?
Have your symptoms been getting any better or worse since they first developed?
Have your symptoms included any mental changes, such as feeling confused, agitated or depressed?
Have you had nausea, vomiting or diarrhea?
Have you felt faint, had seizures or lost consciousness?
Have you had a headache? If yes, has it gotten progressively worse?
Have your symptoms included weakness, fatigue or lethargy?
Do you use recreational drugs? If yes, which drugs?