Hyponatremia: Low Blood Sodium, Causes, Symptoms and Water Intoxication
Low blood sodium (hyponatremia): urgent warning signs, causes such as medicines, heart, kidney and liver disease and overdrinking water, how it is tested, and why treatment is clinician-led.
Content last updated . This page has not been medically reviewed.
Urgent signs come first
Low blood sodium can be a life-threatening emergency. MedlinePlus says to call your provider right away if you have symptoms. [1] Seizures (convulsions), severe confusion, hallucinations or being hard to wake are signs of serious brain involvement. [1] Call emergency services (911 in the US) for those signs. Hyponatremia that appears within 48 hours is more dangerous than the kind that develops slowly over days or weeks. [1]What hyponatremia is
Hyponatremia is a blood sodium level lower than normal. [1] MedlinePlus gives a normal range of 136 to 144 mEq/L (the same number in mmol/L), and notes that ranges vary slightly between laboratories. [1] It is mainly a problem of too much water relative to sodium, not a shortage of salt in the diet. When sodium outside the cells falls, water moves into the cells and they swell. Brain cells are especially sensitive, and this causes many of the symptoms. [1] WHO describes sodium deficiency from diet as extremely unlikely in healthy people. [2]Symptoms
Common symptoms include confusion, irritability, restlessness, fatigue, headache, loss of appetite, nausea or vomiting, and muscle weakness, spasms or cramps. [1] These symptoms are not specific to low sodium, so blood and urine tests are used to confirm it. [1] Severe cases can lead to decreased consciousness, coma, brain herniation and death. [1]Causes the sources name
| Cause | What the source says |
|---|---|
| Fluid losses | Diarrhea, vomiting, sweating and large burns [1] |
| Medicines | Diuretics (water pills) increase urine output and sodium loss [1] |
| Long-term conditions | Heart failure, kidney diseases, cirrhosis [1] |
| Hormone-related water retention | SIADH, where the body does not pass out the right amount of water; it can be caused by some cancers and pituitary tumors [1] |
| Antidepressants (SSRIs) | A literature review found hyponatremia is a potentially serious complication, more common in older people and women, but based mainly on case studies [3] |
| Excess water intake | A systematic review of 590 cases found psychogenic polydipsia (compulsive drinking) in 55%, exercise in 12%; median intake was 8 L a day [4] |
The water-intake review rated its own evidence as low quality (mostly case reports) and noted that water intoxication requires intake far above population recommendations. [4] Of the cases, 53% presented with severe features such as seizures or coma and death occurred in 13%. [4] For endurance events and hot weather see hyponatremia in endurance exercise.
Who is more at risk
From the sources above: people on diuretics or SSRIs, older adults (for SSRIs), and people with heart failure, kidney disease or cirrhosis. [1] [3] Whether other groups such as pregnant women or young children face particular risk is not described in the sources we read, so ask a clinician.Testing and treatment
Tests that help diagnose it include a basic or comprehensive metabolic panel, blood and urine osmolality and urine sodium. [1] Treatment depends on the cause and type. It may include fluids through a vein, medicines to relieve symptoms, or limiting water intake. [1] A review of acute cases suggests that speed of correction matters: slow correction is indicated in chronic cases to avoid neurological complications. [5] Because the right approach differs by type, the sources do not support self-treating with salt or with extra or less water; a clinician decides.Prevention points from the sources
MedlinePlus says treating the underlying cause helps, and that people doing vigorous activity can drink fluids containing electrolytes such as sports drinks to keep sodium in a healthy range. [1] It does not give amounts. Talk to a clinician or pharmacist if you take diuretics, antidepressants or other medicines that may affect sodium; see Medication Interactions. For electrolyte basics see what electrolytes do and electrolyte imbalance.Frequently asked questions
What is the normal blood sodium range?
MedlinePlus gives 136 to 144 mEq/L (136 to 144 mmol/L), and ranges vary slightly by laboratory. [1]
Can drinking too much water cause low sodium?
Yes. A systematic review of 590 cases linked excess water intake to hyponatremia, mostly with compulsive drinking, though evidence quality was low. [4]
Does low blood sodium mean I need more salt?
Not necessarily. MedlinePlus describes it as an imbalance of water and sodium, and treatment depends on the type. [1]
Which medicines can lower sodium?
MedlinePlus names diuretics. [1] A literature review reports SSRIs can cause it, mainly in older people and women. [3] Ask a pharmacist about your own medicines.
When should I get urgent help?
For seizures, confusion or reduced consciousness, call emergency services (911 in the US). MedlinePlus calls severe low sodium a life-threatening emergency. [1]
References
- MedlinePlus (US National Library of Medicine). Review date 5/19/2025. MedlinePlus Medical Encyclopedia, Low blood sodium. Read 2026-10-23.
- World Health Organization. Page dated 11 May 2026. WHO, Sodium reduction (fact sheet). Read 2026-10-23.
- Hyponatremia as a complication of selective serotonin reuptake inhibitors. Journal of the American Academy of Nurse Practitioners 2008. PubMed 18184165. Read 2026-10-23.
- Clinical characteristics and outcomes of hyponatraemia associated with oral water intake in adults: a systematic review. BMJ Open 2021. PubMed 34887267. Read 2026-10-23.
- Acute Dysnatremias - a dangerous and overlooked clinical problem. Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine 2019. PubMed 31138251. Read 2026-10-23.