Taking Lithium: Blood Levels, Kidney and Thyroid Monitoring

Taking lithium means regular blood tests: lithium levels, plus kidney function, thyroid function and calcium. The reason is in the drug's boxed warning: lithium toxicity is closely related to the blood level and can occur at doses close to therapeutic levels. Levels are checked often while the dose is being set, then every few months once you are stable, and again whenever something changes, such as a new medicine or an illness.

Done well, this monitoring is routine and manageable. This guide explains the target ranges, a typical testing schedule, the warning signs of toxicity, the common interactions, and what to do when you are sick.

Why lithium needs blood tests

Lithium is FDA-approved as monotherapy for bipolar I disorder, both to treat acute manic and mixed episodes and as maintenance treatment, in patients 7 years and older. It is also used in other situations, such as adding it to an antidepressant, which is off-label because the label's only indication is bipolar I disorder; see antidepressant augmentation options.

The FDA label puts toxic concentrations at 1.5 mEq/L or above, close to the therapeutic range of 0.8 to 1.2 mEq/L, and notes that some unusually sensitive people show toxic signs within the therapeutic range. Lithium leaves the body through the kidneys, so anything that changes kidney handling of salt and water, such as dehydration, certain medicines or illness, can push the level up without any change in dose. Over years, lithium can also affect the kidneys, thyroid and parathyroid glands, which is why those are tested too.

For how lithium compares with other mood stabilizers, see bipolar disorder medications compared and lithium vs lamotrigine.

Target blood levels

Your prescriber chooses your target, and it may differ from the figures below depending on your history and how you respond. The two main reference points differ somewhat:

The US label reports levels in milliequivalents per liter (mEq/L) and NICE in millimoles per liter; your lab report shows which unit it uses, and your prescriber can explain how your result compares with your target. The label also says that older adults often respond to lower doses and may show toxicity at levels other patients tolerate, and NICE advises checking levels more often in older people.

Timing matters

A lithium level only means something if the blood is drawn at the right time. The label says to draw it just before the next dose, about 12 hours after the previous one. If you take lithium at bedtime, a draw the next morning, about 12 hours later, fits that timing; for any other schedule, ask your prescriber how to time the draw around your doses. Tell the lab and your prescriber when you took the last dose. The label also cautions that levels alone are not enough: how you feel and what the clinician observes matter as much as the number.

A typical monitoring schedule

The FDA label and NICE guidance together give a clear outline. Your prescriber may test more often.

NICE recommends lithium levels every 3 months, rather than 6, after the first year for older people; people taking medicines that interact with lithium; people at risk of kidney or thyroid problems or raised calcium; people with poor symptom control or difficulty taking lithium regularly; and people whose last level was 0.8 mmol per liter or higher.

Keep your results in one place. A simple log of dates, doses, levels and kidney and thyroid results makes it easy to spot a trend, and NICE notes that a falling eGFR over two or more tests should prompt closer monitoring and a review of how fast kidney function is changing. The article on ongoing medication management covers how lab results fit into routine visits.

Reading a result that looks off

A single surprising number is a reason to ask questions, not to change your dose yourself. Common explanations include a blood draw taken too soon after a dose, a missed or doubled dose in the days before, a recent illness, a new medicine, or a stretch of heavy sweating or a change in hard exercise. Your prescriber may simply repeat the test with careful timing before deciding anything.

Brands, generics and formulations

Lithium appears on lists of narrow-therapeutic-index or critical-dose drugs used by medicines regulators, summarized in an FDA presentation, meaning small differences in blood level can matter. If your pharmacy switches you to a different manufacturer or to an extended-release product, tell your prescriber, who may want a level checked. Generic vs brand-name psychiatric medications explains how generic equivalence is judged.

Kidney, thyroid and calcium: what the tests are watching for

Kidneys

Lithium can reduce the kidneys' ability to concentrate urine, sometimes producing nephrogenic diabetes insipidus, with frequent urination and thirst; this can start within weeks. With long-term use, lithium is associated with a form of chronic kidney disease. The label says kidney function should be assessed before and during treatment, and that progressive or sudden changes in kidney function, even within the normal range, mean treatment should be re-evaluated. The label advises avoiding lithium in severe kidney impairment.

Thyroid

Lithium is concentrated in the thyroid and can lead to an underactive thyroid; overactive thyroid has also been reported. Symptoms of an underactive thyroid include fatigue, weight gain and sadness or depression, so a thyroid test is part of checking any new low mood on lithium. When it develops, thyroid hormone replacement can be added rather than stopping lithium.

Calcium and parathyroid glands

Long-term lithium is associated with overactive parathyroid glands and high calcium, which may not resolve when lithium is stopped. The label says to monitor calcium regularly.

If you see a primary care doctor or nephrologist, share your lithium results with them. How your psychiatrist and primary care doctor should work together explains how to keep both informed.

Signs of lithium toxicity

Because lithium can take up to 24 hours to distribute into the brain, symptoms of acute toxicity can appear later than the cause. The label groups neurological signs by severity:

Nausea, vomiting and diarrhea can also be signs of toxicity, and they can cause it by dehydrating you. A fine hand tremor, increased urination and mild thirst are common early in treatment and do not necessarily mean toxicity, but a tremor that becomes coarse or comes with unsteadiness or confusion needs prompt attention. NICE recommends checking for tremor, tingling, unsteadiness and cognitive problems at every appointment, because these can occur even at therapeutic levels.

Medicines and situations that raise lithium levels

The label lists diuretics, NSAIDs, renin-angiotensin system antagonists (ACE inhibitors and angiotensin receptor blockers) and metronidazole as medicines that can increase lithium levels, and says levels should be checked after starting any of them.

• NSAIDs: ibuprofen (Advil, Motrin) and naproxen (Aleve), including over-the-counter brands. NICE advises people on lithium not to take over-the-counter NSAIDs. Ask a pharmacist or your prescriber about pain relief alternatives.
• Blood pressure medicines: diuretics ("water pills"), ACE inhibitors and ARBs. Tell any doctor who prescribes these that you take lithium.
• Metronidazole, an antibiotic.
• Serotonergic medicines, including SSRIs and SNRIs, which raise the risk of serotonin syndrome when combined with lithium.
• Antipsychotics: there have been reports of neurological reactions in people taking lithium with an antipsychotic, ranging from movement side effects to neuroleptic malignant syndrome.

Non-drug situations matter too. The label lists fever, impaired kidney function, dehydration, significant heart disease and changes in sodium or potassium as raising the risk of toxicity, and advises a normal diet including salt and adequate fluids. A sudden low-salt diet, heavy sweating, or a big change in your exercise routine can all shift levels.

When you are sick: plan ahead

NICE advises people taking lithium to seek medical attention if they develop diarrhea or vomiting or become acutely ill, and to keep up fluids, especially after sweating, in hot weather, with fever, or during long periods of immobility. The label adds that infection with fever may require a temporary reduction or pause, under medical supervision.

The safest approach is to agree on a plan with your prescriber before you need it. Ask:

• If I have vomiting, diarrhea or a fever, should I call you, and what should I do with my dose in the meantime?
• Who should I call after hours?
• When should I go to an emergency room instead?
• Should I have a lithium level checked after I recover?

Write the answers down and keep them with your medicines. If you are admitted to a hospital or have surgery, make sure the team knows you take lithium.

Pregnancy, stopping and other special situations

Lithium clearance rises during pregnancy and falls again at delivery, so levels need closer monitoring, and the label describes dose changes around the time of delivery. NICE advises telling your doctor as soon as possible if you become pregnant or plan a pregnancy. Psychiatric medications during pregnancy covers how that decision is weighed.

Do not stop lithium abruptly on your own. NICE warns that poor adherence or rapid discontinuation may increase the risk of relapse, recommends reducing the dose gradually over at least 4 weeks and preferably up to 3 months, and advises close monitoring for early signs of mania or depression during the taper and for 3 months afterward. If you want to stop, raise it with your prescriber so the plan can include early-warning signs to watch for. The practice's article on early warning signs of a bipolar episode is a useful companion.

If you are thinking about suicide or are in crisis, call or text 988 (the 988 Suicide & Crisis Lifeline) or go to the nearest emergency room.

Questions to ask your prescriber

• What lithium level are we aiming for, and why that range for me?
• Where should I get blood drawn, and how do I time it with my dose?
• How often will we check kidney, thyroid and calcium, and who sees the results?
• Which over-the-counter medicines should I avoid, and what can I take for pain?
• What is my plan if I get sick or dehydrated?
• If my kidney function starts to fall, what would we consider?

How the practice approaches it

The practice's prescribers include psychiatrists and psychiatric nurse practitioners, and its ongoing care includes psychiatric evaluation, medication management and lab testing. Whether a specific medication such as lithium, and its monitoring, would be handled there is a question to ask on the free discovery call. Its bipolar disorder treatment page describes the broader approach, and the lab testing page explains how testing fits in. To see how starting care works, read the guide to choosing psychiatric care.

Frequently asked questions

How long after my dose should I get a lithium level drawn?

About 12 hours after your last dose, just before the next one. Tell the lab and your prescriber when you took the last dose so the result can be read correctly.

Can I take ibuprofen while on lithium?

Ask first. NSAIDs such as ibuprofen and naproxen can raise lithium levels, and NICE advises people on lithium not to take them over the counter. Your prescriber or pharmacist can suggest alternatives.

Does lithium always damage the kidneys?

Not necessarily. Lithium can affect kidney function, especially with long-term use, which is why kidney tests are done regularly. Changes found early give you and your prescriber time to adjust the plan.

My thyroid test came back low. Do I have to stop lithium?

Not necessarily. The lithium label notes that thyroid hormone replacement can be used if hypothyroidism develops. Your prescriber and primary care doctor will decide together.

Is it safe to drink alcohol or exercise hard on lithium?

Heavy sweating and dehydration can raise lithium levels, so drink fluids and tell your prescriber before a big change in exercise. Ask your prescriber about alcohol specifically.

Can I switch between lithium brands or formulations?

Only with your prescriber's knowledge. Lithium is a drug where small differences in blood level matter, so your prescriber may want a level checked after any change in manufacturer or formulation.

Sources

1. Lithium carbonate tablets and capsules prescribing information. Hikma Pharmaceuticals / DailyMed (NLM), 2026. dailymed.nlm.nih.gov
2. Bipolar disorder: assessment and management (CG185), Recommendations. National Institute for Health and Care Excellence (NICE), 2014 (updated 2025). nice.org.uk
3. FDA Drug Topics: Understanding Generic Narrow Therapeutic Index Drugs. U.S. Food and Drug Administration (Office of Generic Drugs presentation, W. Jiang), 2022. fda.gov
4. Lithium. MedlinePlus Drug Information, U.S. National Library of Medicine, 2026. medlineplus.gov
5. Hypothyroidism. MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2026. medlineplus.gov

Educational information, not medical, tax or legal advice. Decisions about diagnosis, medication and treatment belong with a clinician who knows your history.