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Lithium
Lithium: Blood Level Checks, Fluid Intake and the NSAID Trap
Lithium is the best-studied medicine for preventing relapse in bipolar disorder, protecting against new manic and depressive episodes. The price for that is a very narrow therapeutic range: there is little distance between an effective and a toxic blood level, which is why regular blood level checks are a fixed part of the treatment. Anything that shifts your fluid and salt balance — heat, diarrhoea, exercise, certain painkillers and blood pressure medicines — can push the level up unnoticed.
Lithium, used as a salt (lithium carbonate, lithium sulfate, lithium acetate)
ATC code
N05AN01
Drug class
Mood stabiliser for relapse prevention; chemically an alkali metal
Dosage forms
Tablets and prolonged-release tablets. The strengths of different preparations are not directly comparable, because they refer to different salts
Half-life
Around one day with normal kidney function; longer in older age and with impaired kidneys
Finding the dose
Cannot be given as a blanket figure in milligrams — the dose is steered by the blood level
Therapeutic range
In relapse prevention usually around 0.5 to 0.8 mmol/l according to the SmPC; set individually
Onset of effect
Full protection only after weeks to months; faster in acute mania
Elimination
Practically entirely through the kidneys, in competition with sodium — hence the sensitivity to losses of salt and fluid
Prescription status
Prescription-only medicine
Notable feature
A very narrow therapeutic range: the effective and the toxic range lie close together. Blood level checks are not negotiable
Table scrolls to the right
2. How it works: what lithium does in the body
Lithium is a special case in the medicine cabinet: not a synthetically developed drug, but a simple metal ion that has been used for decades in the treatment of bipolar disorder. On current knowledge it counts as the most effective agent for preventing relapse — that is, for preventing new manic and depressive episodes.¹,²
To be honest: the exact mechanism of action has still not been fully explained. The efficacy is well documented, the explanation behind it remains patchy. What is mainly discussed is an effect on signal transmission: lithium slows down messenger cascades inside the nerve cell and so damps down excessive swings.
For everyday life another point is the decisive one: lithium is eliminated exclusively through the kidneys, in competition with sodium. If your body has to conserve salt and water, it holds on to lithium as well. Almost every precaution in this article follows from that.
Why lithium does not work like a sedative. Many people expect a noticeable effect on the first day. But lithium does not calm you or lift your mood acutely; it smooths out the swings over months. If you measure the effect on individual days, you will as a rule not find it.
3. Dosing: the blood level determines the dose
With lithium there is no standard dose: the amount that produces the right level in you depends on kidney function, weight, age and salt balance. The figures below describe the usual approach according to the SmPC and the guideline and are not a dosing instruction.¹,²
A cautious start: treatment begins low and is adjusted on the basis of the first level measurements.
Steering by the level: after every dose change another check follows, because a stable value only settles after several days.
Prolonged-release forms release the drug gradually and are often better tolerated. Breaking them up is only allowed if the SmPC provides for it.
Switching preparations: a change of manufacturer is not a routine matter with lithium. Because the strengths refer to different salts, every switch belongs in medical hands, with a level check afterwards. Background in the guide generics vs brand-name medicines.
Do not top up the dose on your own. "Making up" a forgotten tablet by taking a double amount the next day is riskier with lithium than with most other medicines — it pushes the level quickly into a range that causes complaints. What applies in general is explained in the guide missed a medication.
4. Taking it: timing, fluid intake, missed doses
Pick a fixed time and stick to it. Many practices prefer the evening dose, because it automatically puts the blood sample in the morning hours.
Take it with plenty of water. Stomach complaints are less common if lithium is not taken on an empty stomach.
Keep your fluid intake steady. Around two litres a day is a usual guide figure for adults without heart or kidney disease — more important than the number is the consistency.
Do not change your salt intake suddenly. A radical cut in salt lets the level rise, a great deal of salt lowers it. Discuss either beforehand.
Missed dose: as a rule do not make it up if the next dose is close — and never double up.
The rule of thumb for everyday life. Anything that dries you out raises the lithium level: heat, fever, diarrhoea, vomiting, long periods of sweating during exercise, fasting, a lot of alcohol. Details in the guides medications and heat and medications and exercise.
Coffee plays a part too: caffeine slightly increases the elimination of lithium. If you cut your consumption from one day to the next, you can trigger a measurable rise in the level — so change habits slowly. On alcohol, see medications and alcohol.
Blood level checks, dosing times and fluid intake in view
So that your next appointment shows how stable the treatment really is.
A fine tremor of the hands — typical and harmless, made worse by caffeine, stress and lack of sleep. The distinction matters: a coarse, sweeping tremor is something different and a warning sign (section 6).
Excessive thirst and passing water often — lithium affects the kidneys' ability to concentrate urine. Drinking is necessary here; cutting back on fluids would be dangerous.
Weight gain — one of the commonest reasons for stopping on one's own. An often overlooked contribution: calorie-containing drinks used to quench the thirst.
Gastrointestinal complaints — nausea and loose stools, above all in the first few weeks.
Tiredness and damped-down emotions — a point to be taken seriously and raised openly, because it decides whether people stay with the treatment.
Rarer, but worth knowing about
An underactive thyroid: easily treatable and rarely a reason to end lithium (section 9).
Declining kidney function and raised calcium: both can occur with long-term use and usually show up only in the laboratory.
Skin changes: existing psoriasis or acne can get worse.
Side effects that weigh on you belong in a conversation — not endured in silence; how to report them is explained in side effects of medications.
6. Blood level checks: the most important appointment in your treatment
With most medicines the blood test is an extra. With lithium it is part of the treatment itself — because the effective and the toxic range lie close together and you cannot feel in time where you are.¹
In the morning, before the dose. The value is measured as a trough level — at the low point, shortly before the next dose takes effect.
Around twelve hours after the last dose. Hence the evening dose.
Do not take the tablet on the morning of the blood test. Take it with you to the appointment and swallow it straight after the blood has been drawn.
State the time of the last dose. A value without a time is only half the information.
The commonest measurement error. Take your morning tablet before the blood test and you produce a falsely high value — and risk an unnecessary dose reduction. Skip the dose the evening before and you produce a falsely low value. How to make sense of findings is explained in understanding blood values.
During the setting-up phase and after every dose change, checks are close together; in stable long-term treatment the guideline recommends several times a year.² In addition, measurements are taken as the occasion demands: with fever, diarrhoea, vomiting, a heatwave, a new diet, surgery and with every new medicine.
Warning signs of lithium overdose — get medical assessment immediately. Poisoning typically announces itself: a coarse tremor instead of the familiar fine one, persistent vomiting or diarrhoea, confusion and slurred speech, unsteadiness of gait and balance problems, pronounced drowsiness, muscle twitching. Do not take another dose and have the level measured immediately. If consciousness is clouded, if there is severe confusion or a seizure, call the emergency services (112 in Germany).
To put it in perspective: poisoning rarely comes out of the blue, but usually creeps up because the circumstances have changed — a gastrointestinal infection, a heatwave, a new painkiller. That is what the next section is about.
7. The three everyday traps: fluids, NSAIDs, blood pressure medicines
Know these three situations and you have the greater part of the risk under control. All of them work through the same mechanism: they reduce the elimination of lithium through the kidneys — the level rises, without anything having changed in the number of tablets.
Trap 1: Fluid loss
Heat and heavy sweating: a heatwave, the sauna, a summer holiday in the south. The body loses water and salt and holds on to both — and so to lithium as well — more strongly, see medications and heat.
Gastrointestinal infection: vomiting and diarrhoea take a lot of fluid out of you in a short time. With a gastrointestinal infection, lithium belongs in a conversation — not simply swallowed on regardless.
Exercise and endurance effort: a marathon or a long bike ride in the warmth can shift the level, see medications and exercise.
Fasting and fever: when fasting, salt and fluid intake fall at the same time; with a fever the body loses more water even without diarrhoea.
Trap 2: The NSAID trap
The most underestimated interaction in everyday life — because the medicines in question are available without prescription and are often not counted as "proper" medicines. Non-steroidal anti-inflammatory drugs such as ibuprofen, diclofenac and naproxen reduce blood flow to the kidneys and with it the elimination of lithium. The level can rise markedly — even from a single pack bought over the counter.¹
Available without prescription does not mean harmless. On lithium, ibuprofen and diclofenac do not belong in self-medication. If you need a painkiller, paracetamol is as a rule the better-tolerated choice, because it does not affect blood flow to the kidneys in the same way. If an NSAID is necessary, the level is monitored alongside it — an overview in the guide painkillers compared.
Trap 3: Water tablets and blood pressure medicines
Thiazide diuretics such as hydrochlorothiazide: they increase the loss of sodium, whereupon the kidneys hold on to lithium more strongly — the level can rise considerably.
ACE inhibitors and sartans such as ramipril or candesartan: these too can reduce elimination, particularly in older age and with impaired kidney function.
These combinations are not forbidden — many people with high blood pressure need both. But they are started deliberately, with a level check afterwards.
8. Interactions at a glance
Combination
Consequence
What to do
NSAIDs (ibuprofen, diclofenac, naproxen)
The level rises, sometimes markedly
Not in self-medication; discuss paracetamol as an alternative
Thiazide diuretics (e.g. hydrochlorothiazide)
The level rises through loss of sodium
Only under monitoring; check the level after starting and after every dose change
ACE inhibitors and sartans (e.g. ramipril, candesartan)
Reduced elimination of lithium
Combine deliberately, plan for level and kidney checks
Watch for restlessness, tremor, tiredness and weight
A low-salt diet, salt substitutes, electrolyte drinks
They shift the sodium balance and with it the lithium balance
Raise changes in diet beforehand
Alcohol
Dehydrates, increases tiredness and problems with coordination
Be restrained, particularly in the heat
Table scrolls to the right
The list is not complete — and that is precisely the point: where the therapeutic range is narrow, it is worth checking every new preparation against it, including over-the-counter products and supplements. The guide drug interactions and the interaction check in the brite app both help.
Alongside the blood level, three further checks accompany the treatment permanently. They are the reason why taking lithium for decades is safely possible at all.²
Thyroid (TSH): lithium can slow hormone production and trigger an underactive thyroid. The complaints — tiredness, lack of drive, weight gain, feeling cold — resemble those of depression and are easily misread. Treatment is usually with levothyroxine; lithium rarely has to be stopped for it.
Kidney function (creatinine, eGFR): with long-term use kidney performance can slowly decline; where chronic kidney disease is known, checks are closer together. A connection with earlier episodes of poisoning is regarded as plausible.
Calcium, weight and blood pressure: lithium can stimulate the parathyroid glands, which raises the calcium value — usually without symptoms.
Bring your findings with you — or better, the history. A single value says little, a curve over two years says a great deal. How laboratory values can be read is explained in understanding blood values; what applies with impaired kidney or liver function is set out under medications for kidney and liver disease.
10. A look at suicide prevention
Lithium is the only mood stabiliser for which an effect on the suicide rate in its own right has been described over decades. The S3 guideline on bipolar disorder expressly cites this additional benefit as an argument for lithium.² Put soberly: it is a further reason why lithium keeps the rank of a first-line preparation despite the monitoring and the side effects — and it is no substitute for crisis plans, psychotherapeutic support and a network of people around you.
If thoughts of suicide arise. Speak to your treating practice straight away or contact the out-of-hours medical service on 116 117 (in Germany). In an acute crisis the emergency services on 112 or the nearest psychiatric emergency department are the right way to go. Telefonseelsorge, the German emotional support helpline, can be reached round the clock and free of charge on 0800 111 0 111 and 0800 111 0 222.
Lithium is also used in addition to an antidepressant when a depression does not respond sufficiently. This so-called augmentation is established practice, but it is a specialist decision.
11. Special situations: pregnancy, breastfeeding, older age
For a long time lithium in pregnancy was regarded as an absolute taboo. That assessment is out of date: on current knowledge — among others according to Embryotox — lithium is not a blanket exclusion criterion, but it does require careful weighing up and close support.³
Risk of malformations: in the first third of pregnancy an increased risk of certain heart malformations has been described; a targeted ultrasound examination of the baby's heart is therefore standard.
The risk of the alternative: a relapse into a severe episode is likewise dangerous in pregnancy and in the weeks after the birth. Stopping abruptly is therefore rarely the safe option.
Changing levels: kidney performance changes markedly over the course of pregnancy, and again around the birth — the level has to be monitored especially closely.
Plans for a family belong on the table before they become urgent. Plan the conversation early — ideally before contraception is stopped. If a pregnancy is confirmed, do not stop lithium on your own; get in touch straight away. For your bearings, see medications during pregnancy and medications and contraception.
While breastfeeding, lithium passes into breast milk. Breastfeeding is possible with checks on the baby, but it is decided individually.
In older age kidney performance falls, so the level rises on the same dose; tremor and unsteadiness of gait also raise the risk of falls. Lower target levels are therefore aimed for and checks are more frequent — see medications in old age and polypharmacy. Before surgery lithium is often paused briefly, see medications before surgery.
12. Stopping: why never abruptly
If one sentence from this article should stay with you, let it be this one: lithium is not stopped abruptly. Ending it suddenly goes together with a markedly increased risk of a rapid relapse, particularly into a manic episode. It has also been described that starting again after stopping on one's own does not in every case work as well as before.²
"I have been well for years." That is as a rule the result of the prophylaxis, not the end of it.
Burdensome side effects. Tremor, weight gain or a damped-down emotional life are serious reasons — for a conversation about dose and alternatives, not for going it alone.
Wanting a child. See section 11: it can be planned, but not done on the spur of the moment.
If stopping makes medical sense, it happens very slowly, often over months, and with a clear plan for early warning signs. How that works is described in stopping medications; for everyday life with a chronic condition, living with a chronic illness is worth reading.
13. Lithium experiences: what patients really ask
"Does lithium turn me into a different person?"
Some people describe a damped-down emotional life on lithium — fewer highs, but also fewer lows. Others say they are themselves again for the first time in years, because the illness no longer sets the rhythm. Both happen. If you feel flattened, that is a finding, not a flaw of character: often something can be changed through the dose. And it is worth checking whether an underactive thyroid is behind it — that feels very similar.
"I am thirsty all the time and have to get up at night — is that normal?"
Yes, that is one of the typical effects on the kidneys. Handling it, though, is counterintuitive: drinking less in order to sleep through the night is exactly the wrong way — it drives the level up. It makes more sense to spread your fluid intake across the day and cut back a little late in the evening, rather than saving on it overall. If thirst and passing water at night increase sharply, that belongs in a report to your practice.
"I had a fever and diarrhoea — do I need to do anything?"
Yes. That is exactly the situation in which levels rise unnoticed. Drink enough, watch for the warning signs from section 6 and get in touch if the infection lasts longer than a day or two. Many practices set a rule in advance for when to pause and when to measure — ask for it before the situation arises.
For longer journeys to hot regions the same applies in spirit: drink more, take enough supply in your hand luggage and find out beforehand where a level can be measured in an emergency — see medications when travelling and storing medications correctly.
Ibuprofen on lithium? Check first.
The interaction check shows you critical combinations before you take them.
The level is measured as a trough level: in the morning, before the next dose and about twelve hours after the last one. So take your morning tablet only after the blood has been drawn, and note the time of the last dose. A value taken after the dose is falsely high and can lead to an unnecessary dose change.
Typical warning signs are a coarse tremor instead of the familiar fine one, persistent vomiting or diarrhoea, confusion, slurred speech, unsteadiness of gait and pronounced drowsiness. Do not take another dose and have the level measured immediately. If consciousness is clouded or there is a seizure, that is an emergency — call the emergency services (112 in Germany).
Not in self-medication. Anti-inflammatory drugs such as ibuprofen, diclofenac and naproxen reduce the elimination of lithium through the kidneys and can raise the level markedly. Paracetamol is as a rule the better-tolerated alternative. If such a painkiller is medically necessary, the level is monitored alongside it.
Ending it abruptly goes together with a markedly increased risk of a rapid relapse, above all into a manic episode. It has also been described that lithium does not in every case work as well as before once it has been stopped on one's own. If stopping makes sense, it happens very slowly and with a plan for early warning signs.
With heavy sweating the body loses water and salt, which can make the lithium level rise. Drink more than usual, avoid the midday sun and long sessions in the sauna, and for longer stays in hot regions plan a level check before and after the trip. With warning signs such as a coarse tremor or confusion, get medical assessment immediately.
Yes, lithium can slow the thyroid's hormone production and trigger an underactive thyroid. That is why the TSH value is one of the regular checks. The complaints resemble those of depression and are easily misread. An underactive thyroid is as a rule easily treatable and rarely a reason to end lithium.
Summaries of Product Characteristics (SmPCs) for lithium-containing medicines (current version, available through the German medicines information system). pharmnet-bund.de
S3 guideline on the diagnosis and treatment of bipolar disorders (DGBS and DGPPN, AWMF reg. no. 038-019, current version) — German source. awmf.org
Embryotox, Charité — German pharmacovigilance and advisory centre on embryonic toxicology: lithium in pregnancy and breastfeeding. Accessed 2026. embryotox.de
Gesundheitsinformation.de (IQWiG): Bipolar disorder — treatment and relapse prevention. Accessed 2026 — German source. gesundheitsinformation.de
Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM, Germany's federal institute for drugs and medical devices): information on medicines safety, Rote-Hand-Briefe (urgent safety notifications). Accessed 2026 — German source. bfarm.de
gesund.bund.de: Bipolar disorder. Accessed 2026 — German source. gesund.bund.de
Manage lithium safely in everyday life — with brite
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Medical disclaimer: This article is for general information and does not replace medical advice, diagnosis or treatment. Never stop lithium on your own and do not change the dose yourself — ending it abruptly clearly raises the risk of relapse. If there are signs of an overdose such as a coarse tremor, persistent vomiting, confusion or unsteadiness of gait, have the level measured immediately; if consciousness is clouded or there is a seizure, call the emergency services (112 in Germany). The choice of medicine, the target level and the dose are always set individually by the treating practice. Last updated: August 2026.
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