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Medicine interactions

Lithium with NSAIDs, ACE inhibitors and dehydration: keeping levels safe

Lithium has a narrow margin between a helpful level and a toxic one, and the kidneys control that level. Anything that reduces the kidneys' ability to clear lithium, or causes fluid loss, can raise it. This guide covers the combinations and situations the NHS flags, and what to do when you are unwell.

Last checked: 2026-10-03

Key facts

At a glance.

  • Named medicines

    The NHS lists NSAIDs such as aspirin, ibuprofen, celecoxib or diclofenac, ACE inhibitors such as enalapril, lisinopril or ramipril, and diuretics such as furosemide or bendroflumethiazide.

  • Fluid matters

    The NHS says the amount of fluid you drink is very important because it can affect the lithium level in your blood.

  • Low-salt diets

    The NHS advises avoiding a low-sodium diet as it can increase the level of lithium in the blood.

  • Blood test timing

    The NHS says the test needs to be 12 hours after the previous dose, with weekly tests when starting and every 3 to 6 months once stable.

  • Illness

    The NHS advises calling 111 with an illness causing severe diarrhoea, vomiting, high temperature or sweating, or if you are not eating and drinking much.

Why lithium levels are sensitive

Lithium is cleared by the kidneys, and the body handles it much like sodium. When the kidneys retain more sodium, as in dehydration or on a low-salt diet, they also hold on to more lithium. A small rise can matter because the range between benefit and harm is narrow, which is why regular blood tests are part of treatment.

Our guide to lithium toxicity describes the clinical picture. This page focuses on the everyday triggers that push a stable level upwards.

NSAIDs, ACE inhibitors and diuretics

The NHS page on taking lithium with other medicines lists three groups first: NSAIDs for pain and swelling, ACE inhibitors for heart problems or blood pressure, and tablets that make you pass more urine. All three can reduce lithium clearance or alter fluid balance, so levels may rise.

The page also lists certain antidepressants such as fluvoxamine, paroxetine and fluoxetine, antibiotics including oxytetracycline, metronidazole, co-trimoxazole and trimethoprim, and epilepsy medicines including carbamazepine and phenytoin. It says to consult a doctor or pharmacist before starting, stopping or combining any medicine with lithium.

  • NSAIDs: aspirin for pain, ibuprofen, celecoxib, diclofenac.

  • ACE inhibitors: enalapril, lisinopril, ramipril.

  • Diuretics: furosemide, bendroflumethiazide.

  • Some antibiotics, antidepressants and epilepsy medicines.

Dehydration, heat and illness

The NHS common-questions page says fluid intake affects lithium levels and that heat, with more sweating, increases the risk of dehydration. It also says alcohol is likely to make you dehydrated. Diarrhoea and vomiting cause large fluid and salt losses in a short time.

The NHS advises calling 111 if you have an illness that causes severe diarrhoea, vomiting, a high temperature or sweating, or if you are not eating and drinking much. Even ordinary colds can reduce fluid intake, so be mindful during any illness.

Salt, diet and weight-loss plans

The NHS says to avoid a low-sodium diet because it can increase the level of lithium. This matters for people trying fashionable low-salt, very restrictive or crash diets. A significant change in diet or fluid habits is worth discussing with the prescriber before it starts, so that a blood level can be checked.

Monitoring and warning signs

The NHS lithium page says weekly blood tests are needed at first and then every 3 to 6 months once stable, with the test taken 12 hours after the dose. Thyroid and kidney checks are also part of monitoring, because lithium can affect both.

Warning signs of toxicity listed by the NHS include loss of appetite, eyesight problems, feeling very thirsty, feeling or being sick, confusion and blackouts, and shaking, muscle weakness, twitches or spasms. Follow the leaflet and seek urgent advice at once, and call 999 or go to A&E if you take more than prescribed.

Practical safeguards

Keep the lithium alert information with you and show it to every prescriber and pharmacist. Before buying anti-inflammatory painkillers, ask the pharmacist whether they are suitable. Have a sick-day plan agreed with your care team, including who to call and whether to have a level checked.

Our guide to the lithium and diuretic interaction covers one pairing in more detail.

Frequently asked

Questions people ask.

Quick, plain-English answers to the questions we hear most.

  • Can I take ibuprofen with lithium?

    The NHS lists ibuprofen among the NSAIDs that interact with lithium. Ask a pharmacist or your prescriber before taking it, and about alternatives for pain.

  • Why do ACE inhibitors affect lithium?

    The NHS lists ACE inhibitors such as ramipril among the medicines that can change lithium levels. The prescriber will usually arrange extra blood tests if both are needed.

  • Do water tablets matter?

    Yes. The NHS names diuretics such as furosemide and bendroflumethiazide. See our lithium and diuretic guide.

  • What should I do if I have diarrhoea or vomiting?

    The NHS advises calling 111 if you have severe diarrhoea, vomiting, a high temperature or sweating, or are not eating and drinking much.

  • How much should I drink?

    The NHS stresses that fluid intake matters but gives no single figure in the pages we read, so ask your care team what is right for you.

  • Is a low-salt diet safe on lithium?

    The NHS advises avoiding a low-sodium diet because it can increase lithium levels. Discuss any dietary change with the prescriber.

  • When is the lithium blood test taken?

    The NHS says it needs to be 12 hours after you took your medicine, which is why lithium is often taken at night.

  • Are herbal remedies safe with lithium?

    The NHS says there is not enough information to say complementary medicines, herbal remedies and supplements are safe with lithium.

  • What are the signs of too much lithium?

    The NHS lists loss of appetite, eyesight problems, extreme thirst, sickness, confusion, blackouts, shaking and muscle weakness or twitches. Seek urgent advice if they occur.

Where this comes from

Sources and checking.

This guide is for information, not medical advice.

Your GP or consultant knows your history and can tell you which parts apply to you. If your symptoms are severe, rapidly worsening, or come with red-flag features, seek urgent medical care. Figures and availability change, so treat them as a guide and confirm with the provider.

Published 2026-10-03, next review 2027-10-03.

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