Lithium Interactions: How NSAIDs, Diuretics, and Dehydration Raise Toxicity Risk

Getting prescribed lithium for bipolar disorder doesn’t mean you can take any painkiller or diuretic without thinking twice. Even something as simple as ibuprofen for a headache or a water pill for high blood pressure can push your lithium levels into dangerous territory. And it doesn’t take much - just a few days of use, or even mild dehydration from a hot day or stomach bug, can trigger serious side effects. This isn’t theoretical. People have ended up in hospital - and some have died - because these interactions were overlooked.

Why Lithium Is So Sensitive

Lithium isn’t like most medications. It works in a very narrow window: between 0.6 and 1.2 mmol/L in your blood. Go below that, and it might not control your mood swings. Go above it, and you risk toxicity - which can mean shaky hands, confusion, vomiting, or even seizures. Your kidneys handle nearly all of it, filtering out about 95% unchanged. That means anything that messes with kidney function or fluid balance can cause lithium to build up fast.

That’s why age matters. If you’re over 65, your kidneys don’t filter as well. You’re already at 3.2 times higher risk of lithium toxicity, even without other drugs. Add in heart failure, diabetes, or kidney disease, and the danger multiplies. It’s not just about the pills you take - it’s about your whole body’s ability to clear lithium.

NSAIDs: The Silent Lithium Boosters

Non-steroidal anti-inflammatory drugs - think ibuprofen, naproxen, diclofenac, even celecoxib - are among the most common culprits. They reduce inflammation by blocking prostaglandins, which also helps your kidneys filter blood. When those prostaglandins drop, your kidneys slow down lithium clearance by 25% to 50%. In some cases, especially with indomethacin, the increase can hit 60%.

This doesn’t happen slowly. Lithium levels often spike within the first week of starting an NSAID. That’s why doctors warn against taking them regularly if you’re on lithium. Even occasional use - like popping a couple of pills for a bad back - can be risky if you’re not monitored. A case in New Zealand involved a 72-year-old woman who took ibuprofen for joint pain while already on lithium and an ACE inhibitor. Her lithium levels climbed unnoticed. She died from toxicity. Her levels had only been checked sporadically.

Not all NSAIDs are equal. Ibuprofen tends to raise lithium levels by 25-40%. Celecoxib is a bit gentler, around 15-30%. But no NSAID is truly safe. The safest approach? Avoid them entirely. If you need pain relief, talk to your doctor about alternatives like acetaminophen (paracetamol), which doesn’t interfere with lithium.

Diuretics: The Big Three

Diuretics - water pills - are another major red flag. They help with high blood pressure or swelling, but they also reduce the amount of fluid your body holds. Lithium rides along with that fluid. When fluid drops, lithium concentrates in your blood.

Thiazide diuretics like hydrochlorothiazide are the worst offenders. They can push lithium levels up by 25-50% in just 7-10 days. That’s why many doctors avoid prescribing them to people on lithium. Loop diuretics like furosemide (frusemide) are less risky, but still dangerous - they can raise levels by 10-25%. And potassium-sparing diuretics like spironolactone? Their effect is unpredictable. Some studies show a rise; others show no change. The uncertainty makes them risky too.

There’s one twist: not all diuretics raise lithium. Osmotic diuretics like mannitol and carbonic anhydrase inhibitors like acetazolamide actually lower lithium levels by 15-30%. That might sound helpful, but it’s not. It means your mood control could slip, and you’d need a dose adjustment. Either way, it’s a problem that needs medical oversight.

And don’t forget herbal diuretics. Many weight-loss teas and supplements claim to be “natural” and safe. But they work the same way as prescription diuretics - by flushing out fluid. If you’re taking these, your lithium levels could spike without you ever realizing it.

Dehydration: The Hidden Trigger

You don’t need to be on a drug to be at risk. Just getting dehydrated can do it. If you lose 2-3% of your body weight in water - say, from sweating in hot weather, vomiting, diarrhea, or even just forgetting to drink enough - lithium levels can jump 15-25%. That’s enough to cross into toxicity.

This is why travel is a big concern. Flying long-haul, especially in dry cabin air, can dehydrate you without you noticing. Traveling to hot climates? Even more dangerous. Gastroenteritis during a vacation? That’s a perfect storm: vomiting, diarrhea, less fluid intake, and lithium building up. People in these situations need to be warned - and monitored - before they even leave home.

Salt intake matters too. If you suddenly eat less salt - say, switching to a low-sodium diet - your body holds onto lithium. That can raise levels by 10-20%. On the flip side, eating more salt can help lower lithium levels. It’s not about going back to junk food, but about keeping your sodium intake steady. Sudden changes, whether up or down, can throw off your balance.

What to Do If You’re on Lithium

Here’s what actually works in real life, based on clinical guidelines from Australia, New Zealand, and the UK:

1. Avoid NSAIDs if you can. Use paracetamol for pain instead. If you must take an NSAID, use the lowest dose for the shortest time possible.
2. Never start a diuretic without talking to your psychiatrist or doctor. Thiazides are usually off-limits. If you need one, your lithium dose may need to be lowered, and your blood levels checked weekly for the first month.
3. Drink water consistently. Don’t wait until you’re thirsty. Aim for 1.5-2 liters a day, more if you’re active, sick, or in heat. Avoid alcohol and caffeine - they dehydrate you.
4. Don’t change your salt intake suddenly. Eat about the same amount of salt every day. Don’t go low-sodium unless your doctor says so.
5. Get blood tests done regularly. Even if you feel fine, lithium levels should be checked every 3-6 months. After starting a new drug or if you get sick, get tested within a week.
6. Know the early warning signs. Diarrhea, dizziness, drowsiness, shaky hands, or nausea? These are often the first signs of lithium toxicity. Don’t wait. Call your doctor or go to the emergency room.

Some people think, “I’ve been on lithium for years, I know my body.” But lithium doesn’t care how long you’ve been on it. Your kidneys change. Your diet changes. You get older. That’s why monitoring doesn’t stop.

When to Seek Help Immediately

Don’t wait for symptoms to get worse. If you’re on lithium and experience any of these, get medical help right away:

• Severe diarrhea or vomiting
• Confusion, memory problems, or trouble speaking
• Uncontrollable shaking or muscle twitching
• Blurred vision or ringing in your ears
• Seizures or loss of consciousness

These aren’t side effects - they’re signs of lithium poisoning. Left untreated, it can cause permanent kidney damage or death. Emergency treatment involves stopping lithium, IV fluids, and sometimes dialysis.

The Bottom Line

Lithium is a powerful tool for managing bipolar disorder - but it’s not a drug you can treat casually. NSAIDs, diuretics, and dehydration aren’t just minor risks. They’re red flags that can turn a stable treatment into a medical emergency. The good news? These risks are well-known, predictable, and avoidable. You don’t need to stop living - you just need to be smart.

Keep your doctor informed about every medication, supplement, or change in your routine. Stay hydrated. Don’t guess with salt. Get your blood tested. And if something feels off - don’t brush it off. Lithium toxicity doesn’t always come with a warning. But you can stop it before it starts.

Next Steps for Patients

If you’re on lithium, start by reviewing your current medications with your doctor. Make a list of everything you take - even over-the-counter painkillers, herbal teas, or supplements. Ask: “Could this affect my lithium?” Then, set up a hydration and salt intake routine. Drink water daily. Keep your salt intake steady. Get your blood tested on schedule. And if you’re planning to travel, get advice before you go.

Lithium keeps many people stable. But it demands respect. The risks are real - but they’re manageable. You don’t have to live in fear. Just stay informed, stay connected to your care team, and don’t ignore the small things. They’re the ones that matter most.