Hyponatremia from SSRIs: Low Sodium and Confusion Risk in Older Adults

Why Your Antidepressant Might Be Lowering Your Sodium

Imagine waking up feeling off-not sick enough to call a doctor, but not right either. Headache. Nausea. A little confused. You think it’s just aging, or maybe the flu. But if you started an SSRI antidepressant two weeks ago, this could be something far more serious: hyponatremia. It’s not rare. It’s not theoretical. It’s happening to thousands of older adults right now, often unnoticed until it’s too late.

Hyponatremia means your blood sodium is too low-below 135 mmol/L. Sodium isn’t just table salt. It’s what keeps your nerves and muscles working, your brain functioning properly. When it drops too far, your cells swell. Your brain swells. That’s when confusion turns to seizures, coma, or death. And SSRIs? They’re one of the most common triggers.

How SSRIs Cause Low Sodium

SSRIs like sertraline, citalopram, and fluoxetine work by boosting serotonin in your brain. That’s how they help depression. But serotonin doesn’t just affect mood. It also talks to your hypothalamus-the part of your brain that controls water balance. When serotonin levels rise too much, your body releases too much antidiuretic hormone (ADH). That hormone tells your kidneys to hold onto water instead of peeing it out.

Result? You’re drinking the same amount of water, but your body is keeping more of it. Your blood gets diluted. Sodium levels drop. This isn’t dehydration-it’s the opposite. You’re waterlogged, not dry. And your sodium? It’s swimming in too much fluid.

This isn’t guesswork. Studies show a direct link between how strongly an SSRI binds to serotonin transporters and how likely it is to cause hyponatremia. Citalopram? Highest binding. Highest risk. Sertraline? Close behind. Fluoxetine? Still risky. Even paroxetine, often seen as "gentler," carries a real danger.

Who’s Most at Risk?

This isn’t a problem for everyone. But if you’re over 65, you’re in the danger zone. About 1 in 6 older adults starting an SSRI will develop low sodium. Women are more likely than men. People under 60 kg? Higher risk. Anyone on diuretics-especially thiazides like hydrochlorothiazide? Risk jumps 4 times. Kidney trouble? Even worse.

Here’s the scary part: many doctors don’t test for it. A 2023 survey found that over 60% of primary care doctors didn’t know hyponatremia from SSRIs usually shows up between 2 and 4 weeks after starting the drug. Patients? Only 29% were warned about it before taking the pill.

And because symptoms-headache, nausea, dizziness, confusion-look like dementia or just "getting older," they’re often ignored. A 78-year-old woman in a case report was admitted to the ICU after her sodium dropped to 118 mmol/L. She’d been on sertraline for 10 days. Her family thought she was just "acting strange." No one checked her blood.

What the Numbers Don’t Tell You

Let’s talk real numbers. For every 1,000 people taking an SSRI, about 19 will develop hyponatremia. That’s not a tiny risk. That’s like 1 in 50. For someone over 65? It’s closer to 1 in 7. Compare that to mirtazapine, another antidepressant: only 6-7 out of 1,000 develop low sodium. That’s a 3 times lower risk.

And here’s what no one talks about: cost. In the U.S. alone, SSRI-induced hyponatremia costs $1.27 billion a year. Most of that is hospital stays and ER visits. Think about that. Billions spent because a simple blood test could have prevented it.

And the FDA now requires all SSRI labels to include hyponatremia warnings. That’s not a small thing. It means regulators agree: this is a serious, documented danger.

What You Should Do Before Starting an SSRI

If you or a loved one is being prescribed an SSRI, here’s what you need to do-right now:

1. Ask for a baseline blood test for sodium before starting the medication.
2. Request a repeat test exactly two weeks after starting-or after any dose increase.
3. Ask: "Is mirtazapine or bupropion an option?" Both have much lower hyponatremia risk.
4. If you’re over 65, on diuretics, or have kidney issues, insist on monthly sodium checks for the first 3 months.

The American Psychiatric Association and the American Geriatrics Society both say this is standard care. If your doctor says it’s "not necessary," push back. This isn’t bureaucracy-it’s survival.

What If You Already Have Symptoms?

Confusion, nausea, headache, fatigue, muscle cramps-these are early red flags. If you’re on an SSRI and notice them, don’t wait. Get your sodium checked. Now.

If your sodium is below 135, the first step is stopping the SSRI. For mild cases (125-134 mmol/L), fluid restriction to 800-1,000 mL per day often fixes it within 72 hours. No drugs needed. Just water control.

But if sodium drops below 125? That’s an emergency. Hospital. IV fluids. Slow correction. Too fast, and you risk osmotic demyelination-a brain injury that can leave you locked in, unable to speak or move. Doctors have to correct sodium no faster than 6-8 mmol/L in 24 hours. That’s why timing matters.

Alternatives That Are Safer

You don’t have to risk your sodium to treat depression. Here’s what works better for older adults:

• Mirtazapine: Lowest risk. Helps with sleep and appetite too. Often preferred for elderly patients with weight loss or insomnia.
• Bupropion: Doesn’t affect serotonin much. Lower hyponatremia risk. Good if you need energy boost.
• Nortriptyline: A tricyclic with lower risk than amitriptyline. Still needs monitoring, but safer than SSRIs.

SSRIs still have their place-for younger people without other health issues. But for someone over 65? The data is clear: mirtazapine is the smarter first choice.

Why This Is Still Overlooked

Doctors aren’t ignoring this on purpose. They’re overwhelmed. Depression is common. SSRIs are easy to prescribe. Blood tests take time. Patients don’t report vague symptoms. And the benefits of treating depression are real-suicide risk drops, quality of life improves.

But here’s the truth: untreated depression kills. So does hyponatremia. The goal isn’t to avoid SSRIs entirely. It’s to avoid them blindly.

When a 82-year-old woman becomes confused after starting citalopram, and her sodium is 122, the problem isn’t the depression. It’s the lack of testing. The lack of awareness. The assumption that "it’s just aging." That’s what needs to change.

What’s Changing Now

Good news: things are shifting. Between 2018 and 2023, SSRI prescriptions for people over 65 dropped 22%. Mirtazapine prescriptions for the same group rose 35%. That’s not coincidence. That’s doctors learning.

The European Medicines Agency is reviewing SSRI safety. The first clinical algorithm for managing this exact problem was published in March 2024. And by 2027, mirtazapine is expected to be the top antidepressant for seniors.

This isn’t a future warning. It’s happening now. And the people who survive hyponatremia? Many are left with lasting brain fog, balance problems, or memory loss. Recovery takes weeks. Sometimes months.

Bottom Line: Don’t Guess. Test.

If you’re considering an SSRI-or already taking one-don’t assume it’s safe just because it’s common. Ask for a sodium test before you start. Ask for a repeat test two weeks later. Ask about safer alternatives. If you’re over 65, have kidney issues, or take water pills? This isn’t optional. It’s critical.

Depression matters. But so does your brain. And your sodium. One simple blood test can prevent a lifetime of consequences.