Lithium for Mood Disorders: Blood Levels, Side Effects, and Safety

A lithium blood level is a test that measures how much lithium is in your blood so your prescriber can keep it within a safe, effective range. Lithium is a long-established mood stabilizer for bipolar disorder with a narrow safety margin. Common side effects include tremor, thirst, frequent urination and stomach upset. Toxicity can cause vomiting, severe diarrhea, unsteady walking, slurred speech, confusion or seizures and needs emergency care. This article covers blood levels, side effects, interactions, monitoring and pregnancy.

Why lithium blood levels are checked

Lithium levels are targeted within a range your prescriber sets, which can differ for acute mania and for long-term maintenance and may be lower in older adults. Too little may not protect against mood episodes. Too much can cause toxicity. The gap between a helpful amount and a harmful one is smaller than with many other psychiatric medicines, which is why lithium blood levels are part of routine care. The lithium label carries a boxed warning that toxicity can occur at levels not far above the usual treatment range, and kidney disease, heart disease, dehydration and low sodium can raise that risk. Tell your prescriber if any of these apply to you.

The MedlinePlus lithium drug information page explains that people taking lithium need regular blood tests, and that these tests are used together with kidney and thyroid checks. Your clinician decides how often based on your history, your dose and any recent changes.

How the test works

The test is usually a "trough" level, meaning a sample taken at a consistent time after your last dose and before the next one. Many clinics ask for a sample roughly 12 hours after the last dose, but your prescriber or lab will give you the timing that fits your formulation. Taking your morning dose before the blood draw can make the result look higher than your usual level, so ask how to handle the timing on the day of the test.

When levels are checked more often

Clinicians often check more frequently when lithium is started, when the dose changes, or when a new medicine is added. They may also check after an illness with vomiting or diarrhea, after a significant change in diet or fluid intake, or if you develop symptoms that could point to toxicity. Tell your prescriber about these changes so they can decide whether a level is appropriate.

What lithium is used for

Lithium is one of the mood-stabilizing medicines used for bipolar disorder, a condition with episodes of mania or hypomania and often depression. The NIMH page on bipolar disorder and the MedlinePlus bipolar disorder page describe the condition and list mood stabilizers such as lithium among the medicines used to treat it. Your prescriber chooses the medicine that fits you. Clinicians sometimes also use lithium alongside an antidepressant when depression has not responded to other treatment. Our article on bipolar disorder symptoms, types and treatment covers the condition itself.

Lithium can take weeks to show its full effect. Some people also need another medicine, such as an antipsychotic, for the early phase of a manic episode. If you take both, our article on antipsychotic weight and blood sugar checks explains the monitoring that may apply to the second medicine.

Common side effects and what to do about them

Many side effects are most noticeable in the first weeks and may ease as your body adjusts. Others can persist and are worth discussing at your next visit. Side effects that people commonly report include:

• Fine hand tremor. It can be bothersome when writing or holding a cup. Caffeine, other medicines and anxiety may make it more noticeable.
• Increased thirst and frequent urination. Lithium can reduce the kidneys' ability to concentrate urine, which sometimes leads to a condition called nephrogenic diabetes insipidus.
• Nausea, loose stools or stomach discomfort. Taking lithium with food may help, and your prescriber can discuss whether a different formulation is suitable.
• Weight gain. Several factors can contribute, including appetite changes, fluid shifts and thyroid effects.
• Metallic taste, mild fatigue, or "mental dullness". Some people describe feeling slowed down or less sharp.
• Skin changes. Acne or a flare of psoriasis can occur in some people.

Do not change the dose or timing yourself because of side effects. Stopping lithium suddenly may raise the risk of a mood relapse. Call your prescriber so they can adjust the plan.

Signs of lithium toxicity

Toxicity can build gradually or appear quickly, and symptoms can overlap with a stomach bug or a mood change, which can make them easy to miss. Early signs may include a tremor that becomes coarse or worse, persistent vomiting or diarrhea, drowsiness, muscle weakness, a feeling of unsteadiness, or slurred speech. More severe toxicity can bring confusion, muscle twitching, loss of coordination, seizures or loss of consciousness.

Because lithium is cleared by the kidneys, anything that reduces kidney function or lowers body fluid and sodium can raise the level in your blood. The risk can rise even when you take your dose exactly as prescribed.

If you suspect toxicity, do not wait for the next scheduled blood test, because a lithium level can only be measured with a blood draw. Severe symptoms need emergency care (see the box below). If you have a worsening or coarse tremor together with ongoing vomiting or diarrhea, drowsiness or unsteadiness, go to an emergency department or urgent care now so a level can be checked; do not drive yourself if you are drowsy or unsteady. If you may have taken too much lithium, call Poison Control at 1-800-222-1222 and follow its instructions, even if you feel well, because symptoms can be delayed.

Dehydration, heat and diet

Fluid and salt balance can affect lithium levels. Dehydration from vomiting, diarrhea, fever, heavy sweating or hot weather can cause the body to hold on to more lithium. Large changes in sodium intake may also shift levels, and some crash diets or very low-sodium diets could be a concern. You do not need to avoid salt or restrict fluids on your own. Aim for a steady routine, and tell your prescriber if you become ill, start a new diet, or plan strenuous exercise or travel to a hot climate. They can advise whether to check a level or adjust the plan.

Medicines and supplements that can interact with lithium

Some common medicines can increase lithium levels, sometimes substantially, by reducing how much the kidneys clear. Examples that clinicians commonly highlight include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen, including over-the-counter products.
• ACE inhibitors such as lisinopril, and angiotensin receptor blockers (ARBs) such as losartan.
• Thiazide diuretics ("water pills").

Check with your prescriber or pharmacist before starting any of these, including over-the-counter NSAIDs, rather than waiting for symptoms. If one is prescribed or you do use one, ask whether a lithium level should be checked after you start it. Dehydration, a low-sodium diet and hot weather can add to the effect.

Other combinations can add risk in different ways. Lithium combined with some antidepressants or other serotonin-active drugs may add to the risk of serotonin syndrome, which our article on serotonin syndrome warning signs describes. Some antipsychotics may cause additional neurologic side effects when combined with lithium.

Before you start any new prescription, over-the-counter product or supplement, ask your pharmacist or prescriber whether it interacts with lithium. For pain, ask your pharmacist or prescriber which option fits your health, since NSAIDs can raise lithium levels. Do not stop lithium or any blood pressure or heart medicine on your own. Instead, make sure everyone who prescribes for you knows you take lithium.

Long-term monitoring: kidneys, thyroid and calcium

Lithium has effects beyond mood, and clinicians often follow several body systems over time:

• Kidneys. Blood tests of kidney function are commonly done, since lithium is cleared by the kidneys and long-term use can be associated with changes in kidney function in some people.
• Thyroid. Lithium can lower thyroid hormone production, leading to an underactive thyroid in some people. Symptoms such as fatigue, feeling cold, constipation or weight gain overlap with depression, so lab testing helps clinicians tell them apart.
• Calcium. Lithium can be associated with higher calcium levels and effects on the parathyroid glands.
• Weight and heart health. Your clinician may track weight, and may check an ECG if you have heart disease or other risk factors.

These problems are not inevitable. Regular monitoring helps clinicians notice changes early so they can decide whether to adjust treatment.

Pregnancy, breastfeeding and planning ahead

If you may become pregnant, or are pregnant, talk with your prescriber before changing anything. Lithium use in early pregnancy has been associated with a higher chance of certain heart defects in the baby, although the absolute risk appears modest; the lithium label and your prescriber can explain the current evidence. Stopping lithium abruptly can raise the chance of a mood relapse, which carries its own risks. The decision involves weighing both sides, and the best choice differs between people. The MedlinePlus page on pregnancy and medicines offers general guidance on discussing medicines with your care team.

Lithium passes into breast milk, and clinicians may recommend closer monitoring of the infant or may suggest alternatives. Pregnancy also changes how the body handles lithium, so levels may need more frequent checks. Tell your prescriber as early as possible if you are planning a pregnancy or have a positive test.

Mood, safety and when to ask for help

Lithium treatment is one part of a bipolar disorder plan, and mood episodes can still occur. If you notice early signs of mania, such as little need for sleep, racing thoughts or risky spending, or of depression, contact your prescriber. Do not wait for your next appointment.

If you have thoughts of harming yourself or ending your life, call or text the 988 Suicide and Crisis Lifeline at 988. If you are in immediate danger or have already acted on a plan, call 911.

Practical tips for taking lithium safely

• Take it at about the same times each day, as your prescriber directed.
• Keep a list of all medicines and supplements and share it with every clinician and pharmacist.
• Keep lab appointments, and ask how to time your dose before a blood draw.
• If you miss a dose, check the label or call your pharmacist. Do not double up unless instructed.
• Carry a card or note in your phone saying you take lithium, in case you need urgent care.
• Ask your prescriber what to do on sick days with vomiting or diarrhea, so you have a plan before it happens.

The NIMH overview of mental health medications is a useful general reference to read alongside your prescriber's advice.

When to Seek Medical Care