Key Takeaways
- A lithium level is meant to be drawn about 12 hours after your last dose, right before the next one; a test at the wrong time can mislead.
- Levels are checked often at the start and after any change, then every few months once stable.
- The range printed on a lab report is a reference, not your personal target; your prescriber reads the number alongside how you feel.
- Toxicity can happen even at a level that looks normal, and symptoms can show up a day later.
- Vomiting with confusion, severe unsteadiness, slurred speech or a seizure on lithium is an emergency: call 911.
A lithium level is a blood test that measures how much lithium is in your bloodstream. It is the main safety check for anyone taking lithium, because the gap between a helpful amount and a harmful one is narrow. Timing is everything: the label says blood should be drawn just before your next dose, about 12 hours after the last one. This page explains that timing, how often levels are usually checked, how to read the number on your lab report, what can make a level change, and the symptoms that mean a level may be too high.
Get help now if…
Possible lithium toxicity: seek emergency care now
Call 911 or go to the nearest emergency room if someone taking lithium has confusion, severe unsteadiness, slurred speech, muscle twitching or jerking, a seizure, fainting, or an irregular heartbeat, especially with vomiting or diarrhea. Lithium toxicity can be life-threatening and there is no specific antidote.
For questions about a possible overdose or a double dose, call Poison Control at 1-800-222-1222 (free, 24/7). Call your prescriber the same day for new coarse tremor, ongoing diarrhea or vomiting, or feeling unusually drowsy or weak. If you are having thoughts of suicide, call or text 988.
What the test measures and why it matters
The lithium label carries an FDA boxed warning: toxicity is closely related to the amount of lithium in the blood and can occur at doses close to the helpful range. That is why the label says facilities for prompt, accurate lithium testing should be available before treatment even starts.
The blood level is how your prescriber adjusts the dose and checks that it stays safe. It sits alongside the kidney, thyroid and calcium tests explained in lithium for bipolar disorder and the broader schedule in lab monitoring for psychiatric medications.
Timing: the 12-hour rule
The current label says to draw blood immediately before the next dose, when concentrations are relatively stable, which is about 12 hours after the previous dose. This is called a trough level. An older extended-release label says 8 to 12 hours.
In practice, for many people that means:
- Take your evening dose at your usual time the night before.
- Go for the blood draw the next morning before taking any morning dose, unless your prescriber tells you otherwise.
- Write down the exact time of your last dose and tell the lab or your prescriber.
- Take your next dose after the blood is drawn, as prescribed.
A sample taken a few hours after a dose can read falsely high, and one taken many hours late can read low. Either can lead to the wrong decision, so timing matters more than people expect. The timing rule is about the last dose. If other tests, such as fasting glucose, are drawn at the same visit, those may have their own instructions.
How often levels are checked
Schedules vary with the person and the product, and your prescriber sets yours. NICE CG185 gives a typical pattern:
| Stage | NICE CG185 suggestion |
|---|---|
| Starting or after any dose change | One week after, then weekly until the level is stable |
| First year on a stable dose | About every 3 months |
| After the first year | Every 6 months for most people |
| Higher-risk situations | Every 3 months: older adults, people on interacting medicines, people at risk of kidney, thyroid or calcium problems, people who miss doses, or a recent higher result |
The label adds extra checks after starting an interacting medicine, during significant illness, and after a big change in strenuous exercise. NICE recommends weight, kidney function, calcium and thyroid tests every six months as well.
Reading the result on a lab report
A lab report shows your number, the unit, and a reference range printed beside it, often with a flag such as H or L. A few things help when you look at it:
- Units are written as mEq/L (common in U.S. labels) or mmol/L (used by NICE). For lithium, these two units give the same number.
- The printed range is the lab's general reference, not a target set for you. The level your prescriber aims for depends on the phase of illness, how you respond, your age and your kidney function. NICE, for example, describes different aims at different stages of treatment.
- A result inside the printed range does not guarantee safety. The label says some people show toxic signs at levels considered within the usual range, and NICE notes nerve-related side effects can occur at therapeutic levels.
- A result outside the range is not a reason to change your dose yourself. Call your prescriber, who will check timing and symptoms and may repeat the test.
Lithium is one of several bipolar labs. See lab tests for bipolar disorder for the full set.
What can push a level up or down
A level that was stable for months can change quickly. Common reasons include:
- Losing fluid: heat, heavy sweating, fever, vomiting or diarrhea.
- New medicines: NSAIDs like ibuprofen, ACE inhibitors, ARBs, diuretics and metronidazole can raise it; acetazolamide and theophylline can lower it.
- Changes in salt intake or a sudden diet change.
- Kidney function shifting with age or illness.
- Missed or doubled doses, or a switch between lithium products.
Hot-weather tips are in psychiatric medication in extreme heat.
Signs of lithium toxicity
The label groups neurological signs by severity. Stomach symptoms such as nausea, vomiting, diarrhea and bloating are also common. The Medication Guide tells patients to call their provider right away for any symptom of toxicity.
| Severity | Signs listed in the label | What to do |
|---|---|---|
| Mild | Fine tremor, lightheadedness, lack of coordination, weakness | Call your prescriber the same day |
| Moderate | Giddiness, apathy, drowsiness, muscle twitching, unsteady walking, blurred vision, ringing in the ears, slurred speech | Call the prescriber now; go to urgent or emergency care if you cannot reach them |
| Severe | Jerking movements, confusion, seizure, coma | Call 911 |
Two details from the label are easy to miss. First, lithium can take up to 24 hours to move into brain tissue, so symptoms may appear later than the cause, such as a day after a stomach bug started. Second, heart rhythm changes and kidney effects can also occur. There is no specific antidote, which is why early action matters.
Keeping track between visits
A level is a snapshot. A few habits make each one more useful:
- Keep a simple log of each result, the date, and the time of your last dose before the draw.
- Note anything unusual in the days before the test: a stomach bug, a heat wave, a new prescription, a missed dose.
- Ask for copies of results through your patient portal so you can see the trend, not just the latest number.
- If you are sick with vomiting, diarrhea or a fever, ask your prescriber whether a level should be checked sooner than planned.
Bring the log to each visit. Trends over time tell your prescriber more than any single number.
At Willow & Stone
Dr. Stacey Forbes, PMHNP-BC, provides outpatient bipolar care in Arlington, Texas, and by telehealth in Texas, New Mexico, Florida, Alaska, Arizona, Colorado and Washington. Labs are ordered as needed, and results are reviewed with you. Willow & Stone provides outpatient, scheduled care and is not an emergency service. For symptoms in the box above, use 911 or Poison Control first. See bipolar disorder treatment at Willow & Stone or the bipolar disorder guide.
Common Questions
What is a normal lithium level?
Your lab report prints a reference range next to your result, but that range is a general reference, not a target for you. The level a prescriber aims for depends on your phase of treatment, response, age and kidney function, and toxicity can occur even within the printed range. Ask your prescriber what your result means for you.
How long after my last dose should a lithium level be drawn?
The current label says about 12 hours after the previous dose, immediately before the next one. For most people that means a morning blood draw before the morning dose. Tell the lab the time of your last dose.
Do I need to fast for a lithium blood test?
The timing rule for lithium is about your last dose, not food. If other tests are drawn at the same time, such as fasting glucose or lipids, those may need fasting. Check the instructions for your specific lab order.
How often are lithium levels checked?
NICE suggests one week after starting or any dose change and weekly until stable, about every three months in the first year, then usually every six months. Some people need checks every three months long term, and extra tests are done after new medicines or illness.
Can you have lithium toxicity with a normal level?
Yes. The label says some people show toxic signs at levels considered within the usual range, and NICE notes nerve-related side effects can occur at therapeutic levels. Symptoms matter as much as the number.
What does lithium toxicity feel like?
Early signs can include vomiting, diarrhea, a worsening tremor, drowsiness, weakness and clumsiness. More serious signs include slurred speech, muscle twitching, blurred vision, confusion and seizures. Call 911 for confusion, severe unsteadiness or a seizure.
Part of our bipolar disorder guide
Sources & Further Reading
- DailyMed: Lithium carbonate prescribing information and Medication Guide (2026)
- NICE CG185: Bipolar disorder: assessment and management (last updated 2 September 2025)
- VA/DoD Clinical Practice Guideline for the Management of Bipolar Disorder (Version 2.0, 2023)
- Poison Control (America’s Poison Centers): 1-800-222-1222
- NIMH: Bipolar Disorder (NIH Pub. No. 25-MH-8088, revised 2025)
This article is general education, not a diagnosis or advice for your situation. Do not start, stop, or change a medication without talking to the clinician who prescribes it; stopping a mood stabilizer suddenly can trigger relapse.
If you need help right now
Willow & Stone is an outpatient practice and is not an emergency service. If you or someone you care about is in immediate danger, call 911.
For urgent mental health support at any hour, call or text 988 to reach the Suicide & Crisis Lifeline, or text HOME to 741741 for the Crisis Text Line. Both are free, confidential, and available 24/7 nationwide.
Dr. Stacey Forbes, DNP, APRN, PMHNP-BC
Board-certified Psychiatric-Mental Health Nurse Practitioner and founder of Willow & Stone Integrative Mental Health. Nearly two decades of clinical experience; integrative, root-cause psychiatry in person in Arlington and by telehealth. Licensed in Texas, New Mexico, Florida, Alaska, Arizona, Colorado & Washington.
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