Lithium Interactions: NSAIDs, Diuretics, and Dehydration Risks Explained

Getting prescribed lithium for bipolar disorder means you’re on a medication with very little room for error. Even small changes in your body or what you take can push lithium levels into dangerous territory. The difference between effective treatment and serious toxicity is narrow-just 0.6 to 1.2 mmol/L in your blood. That’s why knowing how NSAIDs, diuretics, and dehydration affect lithium isn’t optional. It’s life-saving.

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-like certain drugs or how much water you drink-directly changes how much lithium stays in your system. If your kidneys slow down, lithium builds up. If they flush it out too fast, your mood can become unstable. Either way, you’re at risk.

This is especially true if you’re over 65, have kidney problems, heart failure, or take other medications. Older adults are 3.2 times more likely to develop lithium toxicity. It’s not just age-it’s how the body handles fluid and drugs over time.

NSAIDs: The Silent Lithium Boosters

If you’ve ever taken ibuprofen or naproxen for a headache or sore knee, you might not realize you’re putting your lithium levels at risk. Non-steroidal anti-inflammatory drugs (NSAIDs) block prostaglandins, chemicals your kidneys need to filter blood properly. When those are blocked, lithium clearance drops by 25% to 50%.

Not all NSAIDs are the same. Indomethacin can spike lithium levels by up to 60%. Ibuprofen? Around 25-40%. Celecoxib is a bit gentler, but still risky. The change doesn’t happen overnight-it usually shows up within the first week of starting the NSAID. That’s why many people don’t connect their new dizziness or nausea to their painkiller.

Worse, combining NSAIDs with ACE inhibitors like cilazapril multiplies the danger. One fatal 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 rose unnoticed because monitoring was inconsistent. She died from toxicity.

Diuretics: The Big Three and Their Effects

Diuretics make you pee more. That sounds harmless, but for someone on lithium, it’s a minefield. The type of diuretic matters more than you think.

Thiazides-like hydrochlorothiazide-are the worst offenders. They reduce how much lithium your kidneys flush out, causing levels to jump 25-50% within 7 to 10 days. This isn’t theoretical. Emergency rooms see this combo all the time in older patients being treated for high blood pressure.

Loop diuretics like furosemide (frusemide) are less dangerous but still risky. They can raise lithium levels by 10-25%. That might sound better, but if you’re already borderline, even a 15% rise can push you into toxicity.

Potassium-sparing diuretics like spironolactone? The data is mixed. Some studies show small increases, others show none. But because the risk isn’t zero, doctors still treat them as cautionary.

Then there are the oddballs: osmotic diuretics (like mannitol) and carbonic anhydrase inhibitors (like acetazolamide). These actually lower lithium levels by 15-30%. That’s not helpful-it’s dangerous too. If your lithium drops too low, your mood can crash. You might feel depressed, tired, or anxious. It’s the flip side of the same coin.

And don’t forget herbal diuretics. Many weight-loss teas, supplements, or “natural cleanses” contain ingredients like dandelion, parsley, or juniper. These aren’t regulated, and they can cause dangerous lithium spikes through dehydration-even if you think they’re “safe” because they’re plant-based.

Dehydration: The Hidden Trigger

You don’t need to be sick to be at risk. Even mild dehydration-losing just 2-3% of your body weight in water-can raise lithium levels by 15-25%. That’s the same as skipping a few drinks after a long walk, flying for hours, or sweating through a hot day.

Traveling? If you’re flying to a hot country or spending time in the sun, your body loses more water. Diarrhea, vomiting, or fever? That’s a red flag. The NHS Borders guidelines are clear: drink plenty of fluids, especially in these situations. But most people don’t think of lithium when they’re just trying to recover from a stomach bug.

Sodium intake plays a big role too. If you suddenly cut back on salt-maybe you’re on a low-sodium diet for heart health-your lithium levels can rise by 10-20%. On the flip side, eating more salt can lower them. That’s why consistency matters. Don’t go from salty chips to a no-salt salad without telling your doctor. Small shifts add up.

What Lithium Toxicity Feels Like

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 confusion (47%)
• Tremors in your hands
• Blurred vision (31%)
• Ringing in the ears (tinnitus, 29%)

If you feel any of these and you’re on lithium, don’t wait. Don’t assume it’s just a virus or stress. Get your blood tested. Severe toxicity can lead to seizures, kidney damage, coma, or death. And here’s the scary part: kidney damage from lithium toxicity can be permanent-especially in older adults.

What You Should Do

You don’t have to give up all medications. But you need a plan.

• Avoid NSAIDs if possible. Use paracetamol (acetaminophen) for pain instead. It doesn’t interfere with lithium.
• Never start a diuretic without telling your prescriber. If you’re being treated for high blood pressure or swelling, your doctor needs to know you’re on lithium. They may switch you to a safer option like an ARB or calcium channel blocker.
• Stay hydrated. Drink water consistently-not just when you’re thirsty. Aim for 1.5-2 liters a day unless your doctor says otherwise. Watch for dark urine-it’s a sign you’re not drinking enough.
• Keep your salt intake steady. Don’t go on extreme low-salt diets without supervision. Your lithium level depends on balance.
• Get your lithium levels checked regularly. After starting any new drug, your doctor should check your blood within 7-10 days. For high-risk patients, weekly checks for the first month are standard.
• Know your warning signs. If you feel off, don’t wait. Call your doctor. Bring a list of everything you’re taking, including supplements and over-the-counter meds.

When You Can’t Avoid the Risk

Sometimes, you need an NSAID for arthritis or a diuretic for heart failure. In those cases, your care team must adjust your lithium dose and monitor you closely. That means:

• Lowering your lithium dose before starting the other drug
• Checking lithium levels every week for the first month
• Monitoring kidney function with blood tests
• Using the lowest effective dose of the interacting drug
• Considering a specialist referral if you’re elderly or have multiple health issues

Many electronic health systems now flag these interactions automatically. But as the Medsafe case shows, alerts aren’t enough. Human oversight still matters. You need to be your own advocate.

Final Thought: It’s Not About Fear-It’s About Control

Lithium works. It saves lives. But it’s not a medication you can take on autopilot. The risks with NSAIDs, diuretics, and dehydration are real-but they’re manageable. You don’t need to live in fear. You need to be informed.

Know your numbers. Know your meds. Know your body. If you’re unsure about anything you’re taking, ask. A quick blood test can prevent a hospital trip. A simple conversation with your doctor can keep you stable and safe.