Severe Hyponatremia from Medications: Signs, Risks, and What to Do

When your sodium levels drop too low, your brain starts to swell. It’s not a slow, gentle process-it can happen in hours. And for many people taking common medications, this isn’t rare. Hyponatremia from drugs is one of the most dangerous, yet overlooked, side effects in modern medicine. It doesn’t always show up as a lab anomaly on a routine blood test. Often, it shows up as confusion, nausea, or a sudden seizure-and by then, it’s already an emergency.

What Exactly Is Hyponatremia?

Hyponatremia means your blood sodium level is below 135 mmol/L. Severe cases drop below 120 mmol/L. Sodium isn’t just about salt on your food. It’s the key electrolyte that keeps your cells balanced, especially your brain cells. When sodium drops too fast, water rushes into your brain to even things out. Your brain doesn’t have room to expand. It gets squeezed. That’s when confusion, seizures, and coma start.

Which Medications Cause It?

Not all drugs cause this. But some do-often quietly, without warning. The biggest culprits:

• SSRIs (like sertraline, citalopram, fluoxetine): These antidepressants trigger SIADH-where your body holds onto too much water. About 22% of drug-induced hyponatremia cases come from these.
• Diuretics (especially thiazides like hydrochlorothiazide): These make you pee out sodium. They’re responsible for nearly 30% of cases.
• Antiepileptics (carbamazepine, oxcarbazepine): These can drop sodium by 0.5 to 1.0 mmol/L per day. One patient’s sister had a seizure on oxcarbazepine. Her pharmacist caught it before she started-her sister didn’t.
• MAOIs, ACE inhibitors, NSAIDs: Less common, but still dangerous, especially in older adults.
• MDMA (ecstasy): Even recreational drugs can cause this. People don’t realize it’s not just dehydration-it’s water intoxication.

It’s not about taking one pill. It’s about who’s taking it. People over 65 are 2.7 times more likely to develop it. Women are more at risk than men. And if you’re on more than one of these drugs? Your risk jumps.

How Fast Does It Happen?

This isn’t something that builds over months. It’s fast. Most severe cases show up within 1 to 4 weeks after starting the drug. In 73% of cases, sodium drops below dangerous levels within the first 30 days. That’s why monitoring matters.

One nurse on Reddit described a 72-year-old patient who started sertraline. Within 10 days, sodium dropped from 138 to 118 mmol/L. The doctor called the early nausea and headaches “normal side effects.” Then the patient had a grand mal seizure. That’s not rare. It’s predictable.

What Are the Warning Signs?

The symptoms are easy to miss because they look like other things:

• Confusion (happens in 68% of severe cases)
• Headaches (often dismissed as tension or stress)
• Nausea or vomiting (called “flu-like”)
• Muscle weakness or cramps
• Seizures (22% of cases when sodium is below 115 mmol/L)
• Coma (if untreated)

Over 68% of patients in patient forums say they were first misdiagnosed. “Flu.” “Anxiety.” “Early dementia.” One woman spent weeks in therapy for “depression” while her sodium kept dropping. Her blood test finally caught it.

Why Is This So Dangerous?

Your brain adapts slowly to low sodium. But when it drops fast-like from a new medication-it doesn’t have time to adjust. The swelling happens too quickly. That’s when brain damage starts. And if sodium is corrected too fast later? You risk a different disaster: osmotic demyelination syndrome. That’s when the brain’s protective coating gets ripped off. It can leave you locked-in, unable to speak or move.

Doctors know this. But many still rush correction. The European Society of Endocrinology says: correct no more than 6 mmol/L in 24 hours. The American Society of Nephrology says up to 8-10 mmol/L is okay with close monitoring. Either way, it’s not a DIY fix. It needs hospital care.

Who’s at Highest Risk?

• People over 65: 61% of severe cases
• Women: 57% of cases
• Those on multiple high-risk drugs: Like an SSRI + a diuretic
• People with heart failure, kidney disease, or thyroid problems

It’s not about being “weak” or “fragile.” It’s about biology. Older adults have less kidney reserve. Women have higher levels of antidiuretic hormone. These aren’t accidents. They’re physiological realities.

How Is It Diagnosed?

It’s not hard-but it’s often missed. A simple blood test: serum sodium. If it’s below 135, you’re in the danger zone. If it’s below 125, you need urgent care. But labs don’t flag it unless someone orders it.

The key is suspicion. If you start a new medication and feel weird within 2 weeks-get your sodium checked. No waiting. No “see how it goes.”

There’s a tool called the Hyponatremia Algorithm from the European Hyponatremia Network. It’s used in hospitals and cuts misdiagnosis from 31% to under 11%. But it only works if doctors use it.

What’s the Treatment?

It depends on how fast the sodium dropped and how low it is.

• Severe symptoms (seizures, coma): Hospital. IV saline. Close monitoring. No fast fixes.
• Mild to moderate: Stop the drug. Fluid restriction. Sometimes, salt tablets.
• New option since 2023: Tolvaptan (Samsca). It helps your kidneys flush out water without losing sodium. It’s been shown to correct sodium 34% faster than standard care.

But here’s the catch: if you need the drug-for depression, seizures, or high blood pressure-you can’t just quit it. That’s why recurrence is so common. 33% of people on SSRIs get hyponatremia again, even after stopping and restarting. That’s why alternatives matter.

Can It Be Prevented?

Yes. But only if we change how we prescribe.

• Check sodium before starting high-risk drugs-especially in older adults.
• Check again within 7 days after starting. Then every 3-5 days for the first month.
• Pharmacists should warn patients. Since March 2024, the EMA requires pharmacists to explain sodium risk at pickup for drugs like carbamazepine and SSRIs.
• Ask: “Could this be low sodium?” before writing off symptoms as “side effects.”

One Mayo Clinic patient said their pharmacist caught a dangerous interaction between oxcarbazepine and hydrochlorothiazide before they filled the prescription. “Saved me from what happened to my sister.” That’s not luck. That’s protocol.

Why Isn’t This Done More Often?

Because we’re still treating symptoms, not causes. Only 63% of doctors follow the FDA’s 2022 warning to monitor sodium in the first 30 days. Community clinics do it 47% of the time. Academic hospitals? 82%. That gap kills people.

Dr. Robert Stern put it bluntly in JAMA: “Why aren’t we mandating sodium checks for every patient starting an SSRI or thiazide?” The answer? Cost. Time. Habit. But the cost of a missed diagnosis? A hospital stay. A seizure. A lifetime of disability. It’s $473 million a year in the U.S. alone.

What’s Next?

AI is stepping in. Mayo Clinic’s algorithm analyzes EHR data-meds, age, labs, symptoms-and predicts hyponatremia 72 hours before it happens. Accuracy? 87%. It’s not in every clinic yet. But it will be.

By 2028, cases will rise 22% as the population ages. But if we start checking sodium routinely-especially in the first 30 days of high-risk meds-we could cut severe complications by 38%.

The window between confusion and seizures? As short as 6 to 8 hours. You don’t get a second chance if you wait.

What Should You Do?

• If you’re on an SSRI, diuretic, or antiepileptic: Ask your doctor for a sodium test. Now.
• If you’ve had nausea, headaches, or confusion since starting a new med: Don’t wait. Get tested.
• If you’re a caregiver for an older adult: Watch for sudden changes in behavior. It’s not dementia. It could be low sodium.
• If you’re a pharmacist or nurse: Don’t assume someone else will check. Flag it.

Hyponatremia isn’t rare. It’s predictable. And it’s preventable-if we start looking for it.