Lithium Interactions: NSAIDs, Diuretics, and Dehydration Risks

Lithium is one of the oldest and most effective mood stabilizers for bipolar disorder. But it’s also one of the most dangerous if not managed carefully. A small change in your body-like taking a common painkiller, starting a water pill, or even skipping a few glasses of water-can push lithium levels into the toxic range. And that’s not theoretical. People have ended up in the hospital, or worse, because of these interactions.

Why Lithium Is So Sensitive

Lithium doesn’t break down in your body. It’s filtered out by your kidneys and excreted in urine. About 95% of it leaves your system unchanged. That means anything that affects your kidneys or your fluid balance directly affects how much lithium stays in your blood.

The safe range is tiny: between 0.6 and 1.2 mmol/L. Go above that, and you risk toxicity. Go below, and your mood may not be controlled. There’s no room for guesswork. This is why even small changes-like starting a new medication or getting sick-can be dangerous.

Older adults are especially at risk. People over 65 are more than three times as likely to experience lithium toxicity. That’s because kidney function naturally declines with age. If you’re also taking other medications or have heart or kidney problems, your risk goes up even more.

NSAIDs: The Silent Lithium Boosters

Non-steroidal anti-inflammatory drugs (NSAIDs) are everywhere. Ibuprofen. Naproxen. Celecoxib. Even aspirin, in high doses. They’re used for headaches, arthritis, menstrual cramps-everything.

But here’s the problem: NSAIDs reduce blood flow to the kidneys by blocking prostaglandins. That slows down how fast your kidneys clear lithium. The result? Lithium builds up in your blood.

The increase isn’t small. Indomethacin can raise lithium levels by 30-60%. Ibuprofen? 25-40%. Celecoxib? Still 15-30%. And it doesn’t take long. Toxicity can show up within a week of starting an NSAID.

One fatal case in New Zealand involved a 72-year-old woman taking lithium, an ACE inhibitor, and an NSAID. Her lithium levels weren’t checked regularly after she started the painkiller. She died from toxicity. That wasn’t an accident. It was a preventable mistake.

There’s no safe NSAID if you’re on lithium. Even occasional use can be risky. The best advice? Avoid them completely. If you must use one-say, for a bad back flare-up-talk to your doctor first. Use the lowest dose for the shortest time possible. And get your lithium level checked within 7-10 days.

Diuretics: Water Pills That Can Sink You

Diuretics, or water pills, are prescribed for high blood pressure, heart failure, or swelling. But they’re a major red flag for lithium users.

Thiazide diuretics-like hydrochlorothiazide-are the worst offenders. They can spike lithium levels by 25-50% within 10 days. Why? They make your kidneys reabsorb more sodium-and lithium rides along with it. Your body thinks it’s saving salt, but it’s accidentally holding onto lithium too.

Loop diuretics like furosemide (frusemide) are less risky, but still dangerous. They can raise lithium levels by 10-25%. Potassium-sparing diuretics like spironolactone? The data is mixed. Some studies show a rise, others don’t. Better to assume risk.

There’s one twist: some diuretics actually lower lithium levels. Osmotic diuretics like mannitol and carbonic anhydrase inhibitors like acetazolamide increase urine output in a way that flushes lithium out. That’s not a good thing either. It can make your mood unstable.

Herbal diuretics? Don’t be fooled. Weight-loss teas, supplements labeled “natural detox,” or even dandelion root pills can cause dangerous lithium spikes. They’re not regulated. They don’t come with warnings. And they can dehydrate you just like prescription diuretics.

Dehydration: The Hidden Trigger

You don’t need a drug interaction to trigger lithium toxicity. Sometimes, it’s just not drinking enough water.

Lithium levels rise when your blood gets more concentrated. That happens when you lose fluids-through sweat, fever, vomiting, or diarrhea. Even a 2-3% drop in body weight from dehydration can increase lithium levels by 15-25%.

Think about this: You’re traveling overseas. It’s hot. You get sick with the stomach flu. You’re not eating, not drinking much, and you’re sweating. You’re still taking your lithium. That’s a perfect storm.

Same thing happens after intense exercise, long flights, or even just spending a day in the sun without enough fluids. People in tropical climates, like parts of Australia, are especially vulnerable. That’s why doctors warn lithium patients to keep drinking water-even if they don’t feel thirsty.

And it’s not just water. Salt matters too. Eating less salt-like on a low-sodium diet-can cause lithium levels to rise. Eating more salt can lower them. A change of just 20-30 mmol of sodium per day can shift lithium levels by 10-20%. That’s why consistency is key. Don’t suddenly cut back on salt or go on a cleanse. Keep your diet steady.

Symptoms of Lithium Toxicity: Don’t Wait

Toxicity doesn’t always come with a siren. Early signs are easy to miss:

• Diarrhea (68% of early cases)
• Lightheadedness or dizziness (52%)
• Drowsiness or fatigue (47%)
• Tremors in your hands
• Nausea or vomiting

If you ignore these, it gets worse:

• Blurred vision (31%)
• Ringing in the ears (tinnitus, 29%)
• Muscle weakness or twitching
• Confusion or slurred speech
• Seizures or coma (in severe cases)

Once you reach this stage, you need emergency treatment. And even if you survive, kidney damage can be permanent-especially if you’re older or already have kidney issues.

What You Should Do

If you’re on lithium, here’s what actually works:

1. Avoid NSAIDs. Use acetaminophen (paracetamol) for pain instead. It doesn’t interfere with lithium.
2. Don’t start diuretics without talking to your doctor. If you need one for blood pressure, your doctor might switch you to a different class of medication, like an ARB or calcium channel blocker.
3. Drink water daily. Aim for 1.5-2 liters unless your doctor says otherwise. Keep a bottle with you. Set reminders if you forget.
4. Keep your salt intake consistent. Don’t go on extreme low-salt diets. Don’t suddenly eat a lot of salty food. Balance matters.
5. Get your lithium levels checked regularly. At least every 3-6 months. More often if you’re over 65, have kidney problems, or start a new medication.
6. Call your doctor immediately if you get sick with vomiting, diarrhea, or fever. Don’t wait. Get tested.
7. Check all supplements. Many herbal products contain diuretics or affect kidney function. Always tell your prescriber what you’re taking.

Monitoring Is Non-Negotiable

Guidelines from Australia, New Zealand, and the UK all say the same thing: monitor lithium levels closely after any change.

If you start an NSAID or diuretic, check your lithium level within 7-10 days-and again at 2-4 weeks. Keep checking every few weeks until it stabilizes. Some doctors recommend weekly checks for the first month.

And don’t assume your doctor will catch it. Electronic systems flag these interactions, but many still miss them. That 72-year-old woman in New Zealand? Her system flagged the interaction. But no one followed up. That’s why you have to be your own advocate.

If you’re on long-term lithium, ask for a shared care plan with a renal specialist or psychiatrist. They’ll know how to adjust your dose and monitor your kidney function properly.

The Bottom Line

Lithium works. It saves lives. But it doesn’t forgive mistakes.

NSAIDs, diuretics, and dehydration aren’t just “possible” risks. They’re proven, common, and deadly. The data is clear. The warnings are out there. The problem isn’t lack of knowledge-it’s lack of action.

If you’re on lithium, treat your body like a precision instrument. Small changes matter. Stay hydrated. Avoid unnecessary meds. Keep your salt steady. Get your levels checked. And never assume someone else is watching out for you.

Your mood stability depends on it.