Lithium Interactions: NSAIDs, Diuretics, and Dehydration Risks Explained

When you're taking lithium for bipolar disorder, even small changes in your body can push your lithium levels into dangerous territory. It's not just about the pill you take every morning-it's about what else you're taking, how much water you're drinking, and even how much salt you're eating. Lithium has a very narrow window where it works safely: between 0.6 and 1.2 mmol/L. Go just a little above that, and you risk serious, even life-threatening toxicity. And the biggest threats? Common medications like NSAIDs and diuretics-and something as simple as not drinking enough water.

Why Lithium Is So Sensitive

Lithium doesn't break down in your body. About 95% of it leaves through your kidneys, unchanged. That means anything that affects how your kidneys work can change how much lithium stays in your blood. If your kidneys slow down-even a little-lithium builds up. And because the difference between a therapeutic dose and a toxic one is so small, even minor changes can be dangerous.

This is why people over 65, those with kidney problems, or anyone with heart failure are at much higher risk. Studies show older adults have more than three times the risk of lithium toxicity compared to younger patients. It’s not just age-it’s how the body changes with age. Kidneys don’t filter as well. Blood volume drops. And the body holds onto sodium and water differently.

NSAIDs: The Silent Lithium Boosters

NSAIDs-like ibuprofen, naproxen, and diclofenac-are among the most common drugs people take for headaches, arthritis, or back pain. But if you're on lithium, they can be risky.

These drugs block prostaglandins, chemicals your kidneys use to keep blood flow steady. When prostaglandins drop, your kidneys filter less blood. That means less lithium gets flushed out. Lithium levels can jump 25% to 60% within just a few days of starting an NSAID.

Not all NSAIDs are the same. Indomethacin is the worst offender-it can spike lithium levels by up to 60%. Ibuprofen raises them by 25-40%. Celecoxib is a bit safer, but still risky, with increases of 15-30%. Even occasional use can be dangerous, but regular use is far more problematic.

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. She developed severe toxicity and died. That’s not rare. It’s a warning.

Diuretics: The Big Problem with Thiazides

Diuretics help lower blood pressure by making you pee more. But they also change how your kidneys handle lithium.

Thiazide diuretics-like hydrochlorothiazide-are the biggest concern. They cause lithium levels to rise by 25-50% within 7 to 10 days. That’s fast. And the rise doesn’t stop after a few days-it keeps climbing if you keep taking them.

Loop diuretics like furosemide are less likely to cause big spikes, but they still raise lithium levels by 10-25%. That’s enough to cause symptoms like dizziness, tremors, or confusion.

Potassium-sparing diuretics like spironolactone? The data is mixed. Some studies show small increases, others show no effect. But because the risk isn’t zero, doctors still advise caution.

And then there are the ones that actually lower lithium: osmotic diuretics like mannitol and carbonic anhydrase inhibitors like acetazolamide. These reduce lithium levels by 15-30%. That’s dangerous too-because now your mood might become unstable.

Herbal Diuretics? Don’t Be Fooled

You might think “natural” means safe. But herbal weight-loss teas, supplements labeled as “detox” or “water pills,” and even some traditional remedies can contain diuretic herbs like dandelion, parsley, or hibiscus. These work the same way as prescription diuretics-they make you lose fluid and salt.

In one case, a patient on lithium started taking a popular herbal tea for weight loss. Within two weeks, her lithium levels doubled. She ended up in the hospital with confusion and vomiting. She didn’t tell her doctor about the tea because she thought it was “just herbal.”

If you’re on lithium, assume every herbal product that makes you pee more is risky. Always check with your prescriber before taking anything labeled as a “natural diuretic.”

Dehydration: The Hidden Trigger

Lithium is carried in your blood. When you lose water-through sweating, vomiting, diarrhea, or just not drinking enough-your blood gets thicker. That means the same amount of lithium is now in less fluid. Your lithium concentration rises.

Even mild dehydration-losing just 2-3% of your body weight in water-can increase lithium levels by 15-25%. That’s enough to trigger symptoms.

This is why travel is risky. Long flights, hot weather, or illness like gastroenteritis can leave you dehydrated without you realizing it. The NHS and Medsafe both warn that people on lithium traveling to hot climates or with stomach bugs need extra care.

You don’t need to drink 10 glasses of water a day. But you do need to drink enough to keep your urine pale yellow. If it’s dark, you’re not drinking enough.

Salt Matters More Than You Think

Your body holds onto lithium when it holds onto sodium. So if you suddenly eat less salt-maybe you’re trying to go low-sodium for your heart-your lithium levels can climb.

Conversely, eating more salt can lower lithium levels. A change of 20-30 mmol of sodium per day (about 1-1.5 teaspoons of salt) can shift lithium levels by 10-20%.

That’s why consistency matters. Don’t go from eating lots of salty snacks to a strict low-salt diet without telling your doctor. And don’t suddenly start using salt substitutes-they often contain potassium, which can also interfere with lithium.

What to Do If You Need an NSAID or Diuretic

Sometimes you can’t avoid these drugs. Maybe you have arthritis and need ibuprofen. Or you have high blood pressure and your doctor says you need a diuretic.

Here’s what to do:

• Always tell your psychiatrist or GP you’re on lithium before starting any new medication-even over-the-counter ones.
• Ask if there’s a safer alternative. For pain, acetaminophen (paracetamol) is usually fine with lithium.
• If you must take an NSAID or diuretic, your lithium level should be checked within 5-7 days and again at 2-4 weeks.
• Reduce your lithium dose before starting the new drug if your doctor advises it.
• Never stop your lithium suddenly. Even if you feel fine, stopping can cause a relapse of mania or depression.

Recognizing Lithium Toxicity Early

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

Later signs are more serious:

• Blurred vision (31%)
• Ringing in the ears (tinnitus, 29%)
• Loss of coordination
• Seizures or coma (in severe cases)

If you notice any of these, stop taking the NSAID or diuretic and contact your doctor immediately. Don’t wait. Lithium toxicity can cause permanent kidney damage, especially in older adults.

Monitoring Is Non-Negotiable

Regular blood tests are the only way to know your lithium level is safe. Guidelines say:

• Check lithium levels before starting any new medication that could interact.
• Test again 5-7 days after starting an NSAID or diuretic.
• Test again at 2-4 weeks.
• Test every 3-6 months if you’re stable, but more often if you’re elderly or have kidney issues.

Many patients don’t get tested often enough. One case report showed a patient’s lithium levels were only checked “sporadically” after starting an NSAID-and she died from toxicity. That shouldn’t happen.

Your doctor should be coordinating with your renal specialist if you have kidney problems or are on long-term lithium therapy. Shared care isn’t optional-it’s essential.

Bottom Line: Stay Informed, Stay Hydrated, Stay Connected

Lithium saves lives. But it demands respect. It’s not just a mood stabilizer-it’s a drug that reacts to your body’s changes. NSAIDs, diuretics, dehydration, and salt changes aren’t small things. They’re red flags.

If you’re on lithium:

• Drink water regularly, especially when sick, hot, or traveling.
• Avoid NSAIDs unless your doctor says it’s safe-and even then, use the lowest dose for the shortest time.
• Never start a new diuretic, herbal product, or salt substitute without checking in.
• Know the early signs of toxicity.
• Keep your blood tests on schedule.

Your mental health matters. But so does your physical health. The two are connected. Stay alert. Stay informed. And never assume something is safe just because it’s common or labeled “natural.”