Mental health
Lithium
A mood stabiliser — A highly effective mood stabiliser for bipolar disorder — with a narrow safety margin that demands monitoring.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Lithium is a long-term treatment for bipolar disorder — used both to treat episodes and, especially, to prevent them — and sometimes to augment antidepressants in resistant depression. It is initiated and supervised with regular blood monitoring.
How it works
Its precise action is not fully understood, but it modifies several signalling pathways inside brain cells in a way that stabilises mood over time. Because it is a small ion handled by the kidneys much like sodium, the body's salt and water balance directly affects its blood level — which is the root of both its monitoring needs and its interactions.
In practice
In practice lithium is one of the most effective treatments in psychiatry — for preventing both the highs and lows of bipolar disorder and for reducing suicide risk — but its narrow therapeutic window makes structured monitoring non-negotiable. Levels are checked regularly (taken about twelve hours after the dose), and the brand is kept consistent because preparations are not interchangeable. The big destabilisers of lithium level are anything that affects fluid and kidney handling: dehydration, vomiting or diarrhoea, a new NSAID, an ACE inhibitor/ARB or a diuretic, and even a low-salt diet can all push the level up towards toxicity. Long-term it can affect the thyroid, the parathyroid (calcium) and the kidneys, so thyroid, calcium and renal function are tracked alongside levels. Patients are taught the warning signs of toxicity — coarse tremor, vomiting and diarrhoea, drowsiness, slurred speech and unsteadiness — and given a clear plan to hold the dose and seek help if they become acutely unwell or dehydrated.
Examples
Practical use
How to take it & use it well
- Take lithium exactly as prescribed and stay on the same brand, as different brands are not always interchangeable.
- Attend your regular blood tests; the blood sample for a lithium level is usually taken about twelve hours after your last dose so timing matters.
- Keep your fluid and salt intake steady - drink enough, especially in hot weather, during illness with vomiting or diarrhoea, or with heavy exercise.
- Avoid anti-inflammatory painkillers unless advised, as they and some other medicines can raise lithium to dangerous levels.
- Learn the signs of lithium toxicity - worsening tremor, vomiting, diarrhoea, drowsiness, slurred speech or unsteadiness - and seek urgent help if they occur.
Common uses
- Maintenance and treatment in bipolar disorder
- Reduction of suicide risk
- Augmentation in treatment-resistant depression
Monitoring
- Lithium level regularly (sampled ~12 hours post-dose), more often after any change
- Thyroid function, calcium and renal function periodically
- Hydration and any new interacting medicines or illness
Weighing it up
Advantages & disadvantages
Advantages
- An effective long-term treatment for bipolar disorder, helping prevent both manic and depressive episodes.
- Can reduce the risk of suicide in people with mood disorders.
- Long-established treatment with well-understood monitoring.
- Sometimes added to antidepressants to boost their effect in difficult depression.
Disadvantages
- Has a narrow safety margin, so regular blood-level monitoring is essential.
- Toxicity can be triggered by dehydration, salt changes or interacting medicines, and can be serious.
- Long-term use can affect the thyroid and kidneys, needing periodic checks.
- Common effects include tremor, increased thirst and urination, and weight gain.
Key safety principles
What to watch for
- Narrow therapeutic range — toxicity is precipitated by dehydration, illness, low salt, and interacting drugs (NSAIDs, ACE inhibitors/ARBs, diuretics).
- Long-term effects on the thyroid, parathyroid (calcium) and kidneys.
- Keep the same brand; recognise toxicity signs (coarse tremor, vomiting/diarrhoea, drowsiness, slurred speech, unsteadiness); it is teratogenic.
Key interactions
What to avoid or check alongside
- NSAID painkillers (such as ibuprofen): reduce lithium clearance and can raise levels into the toxic range.
- Diuretics (water tablets), especially thiazides: can raise lithium levels and cause toxicity.
- ACE inhibitors and similar blood-pressure medicines: can increase lithium levels.
- Significant changes in salt intake or dehydration: can raise lithium levels.
- Some antidepressants and other serotonergic drugs: combined use needs care due to added effects.
Patient & carer advice
- Keep well hydrated and seek advice if you have a fever, vomiting or diarrhoea
- Do not start ibuprofen-type painkillers or change your salt intake without advice
- Attend your blood tests, stick to the same brand, and learn the toxicity warning signs
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Lithium: frequently asked questions
Why is the timing of my lithium blood test important?
The lithium level is usually measured about twelve hours after your last dose, as this gives a standard, comparable reading. Taking the sample too early or late can give a misleading result and affect dosing decisions.
Why must I keep my fluid and salt steady?
Lithium levels rise if you become dehydrated or your salt intake drops, increasing the risk of toxicity. Drink enough fluids, take extra care in hot weather or illness, and avoid sudden major changes to your diet.
What are the signs of lithium toxicity?
Warning signs include a worsening hand tremor, vomiting, diarrhoea, drowsiness, slurred speech, blurred vision and unsteadiness. If these occur, seek urgent medical help, as toxicity can become serious quickly.
Why should I avoid ibuprofen on lithium?
Anti-inflammatory painkillers reduce how well the kidneys clear lithium, which can push levels into the toxic range. Use alternative pain relief such as paracetamol unless your clinician has advised otherwise.
Why must I stick to the same brand of lithium?
Different lithium brands can release the drug slightly differently, so switching can change your blood levels. Staying on the same brand keeps your levels stable and your monitoring reliable.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
Related guides
Need a custom medicines or prescribing resource?
We build evidence-led clinical references, calculators and decision aids for teams.