Lithium

Mood stabilizer, Antimanic agent, Narrow therapeutic index medicine

Lithium

Lithobid (lithium carbonate extended-release, 300 mg and 450 mg tablets); Lithium carbonate immediate-release tablets and capsules (150/300/600 mg; multiple generics); Lithium citrate oral solution (8 mEq/5 mL, approximately equivalent to 300 mg lithium carbonate per 5 mL).

Lithium is an inorganic alkali metal ion (atomic number 3) used as a mood stabilizer, with the strongest long-term evidence base for bipolar disorder maintenance of any currently available psychotropic medicine. It is the only psychotropic with a robust evidence base specifically for suicide reduction across both bipolar and unipolar depressive disorders -- a clinically important distinction. It has been in continuous clinical use since 1949, making it one of the oldest psychotropic medicines in modern psychiatry.

Lithium's key limitation is its extremely narrow therapeutic index: the difference between the therapeutic serum level (0.6-1.2 mEq/L) and the toxic level (>1.5 mEq/L) is small, and toxicity can be severe and potentially fatal. Mandatory serum level monitoring and careful management of interacting factors (sodium intake, hydration, renal function, interacting medicines) are essential throughout treatment.

Lithium is renally eliminated without any hepatic metabolism -- a unique pharmacokinetic property among psychotropics, with major clinical implications. Its renal handling mimics sodium: filtered at the glomerulus and extensively reabsorbed in the proximal tubule in competition with sodium. Any condition causing sodium depletion or volume contraction (low-salt diet, dehydration, diuretics, ACE inhibitors) increases proximal tubular lithium reabsorption and can raise lithium to toxic levels. This mechanism explains the majority of lithium's clinically important drug and dietary interactions.

The discovery of lithium's antimanic properties by John Cade in 1949 is a foundational moment in modern psychopharmacology; it preceded the development of chlorpromazine and represented the first effective pharmacotherapy for any psychiatric condition.

History

Discovery by Cade (1949): John Frederick Joseph Cade, an Australian psychiatrist working at the Bundoora Repatriation Mental Hospital in Victoria, discovered lithium's antimanic properties through a serendipitous experiment in 1948-1949. While investigating the hypothesis that manic episodes involved excess uric acid, Cade injected guinea pigs with lithium urate -- using lithium as a solubilizing agent -- and observed unexpectedly that the animals became calm and sedated. He then administered lithium carbonate to manic patients, with striking results. His 1949 report in the Medical Journal of Australia described 10 manic patients treated with lithium, all of whom improved significantly.^{[citation needed]}

The discovery was largely ignored initially because of near-simultaneous reports of lithium toxicity (it had been sold as a sodium-salt substitute in cardiac patients in the late 1940s, causing deaths from unrestricted use without monitoring) and because Cade was working in a remote institution without academic connections to amplify the finding.

Schou and controlled trials (1950s-1960s): The Danish psychiatrist Mogens Schou conducted the first controlled trials of lithium in mania and, with Poul Christian Baastrup, established the prophylactic efficacy of lithium in preventing recurrent manic and depressive episodes in bipolar disorder. Schou's decades of work transformed lithium from a clinical curiosity into a mainstream treatment. He also conducted early studies on lithium teratogenicity (contributing to the International Register of Lithium Babies in the 1970s) and was later involved in correcting the teratogenic risk overestimate.^{[citation needed]}

FDA approval (1970): The FDA approved lithium (as Eskalith) for acute manic episodes in 1970 -- the first FDA-approved treatment for any phase of bipolar disorder and the first psychotropic approved based on documented serum level monitoring as a condition of use.

Ebstein's anomaly scare and re-evaluation (1975-2017): The International Register of Lithium Babies was established in the early 1970s to collect cases of lithium-exposed pregnancies; a voluntary registry of this type is inherently subject to ascertainment bias (adverse outcomes more likely to be reported). The 1975 registry report suggested a markedly elevated risk of Ebstein's anomaly. This led to widespread contraindication of lithium in pregnancy for decades. The risk was subsequently substantially revised downward by population-based cohort studies, culminating in the landmark 2017 NEJM study by Patorno and colleagues.

BALANCE trial (2010): The BALANCE randomized trial demonstrated lithium superiority to valproate for long-term prophylaxis in bipolar I disorder, providing the most rigorous comparative evidence for lithium's maintenance advantage.^{[citation needed]}

Experience

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Problems

Bipolar I Disorder★★★★★★★★★★★★★★★—××

Acute manic episodes in bipolar I disorder; FDA-approved. Effective for euphoric/classic mania; dysphoric or mixed-state mania may respond less well. Co-administration with a neuroleptic or benzodiazepine is standard for acute behavioral management while lithium is titrated to therapeutic levels.

Bipolar II Disorder★★★★★★★★★★★★★★★—××

Bipolar II disorder maintenance; FDA maintenance label covers the full bipolar spectrum; lithium evidence is strongest for bipolar I but extends to bipolar II prophylaxis.

Bipolar Disorder★★★★★★★★★★★★★★★—××

Bipolar disorder maintenance prophylaxis (all subtypes); the strongest long-term evidence base of any mood stabilizer. The BALANCE trial (2010) showed superiority to valproate monotherapy for bipolar I. Data from long-term cohort studies support lithium as the reference comparator for bipolar maintenance.

Treatment-resistant depression (augmentation)★★★★★★★★★★★★★★★—××

Treatment-resistant depression augmentation; one of the best-evidenced augmentation strategies in psychiatry. CANMAT and NICE guidelines list lithium augmentation as a first-line option for antidepressant-resistant depression.

Suicidal Behavior★★★★★★★★★★★★★★★—××

Suicidal behavior (off-label); the strongest pharmacological anti-suicidal evidence of any psychotropic, spanning suicidal ideation through completed suicide across both bipolar and unipolar diagnoses. Meta-analyses consistently show significantly reduced suicidal behavior in lithium-maintained patients; the anti-suicidal mechanism may be independent of mood stabilization.

Cluster headache★★★★★★★★★★★★★★★—××

Cluster headache prevention (off-label; modest evidence).

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Titration strategies

Acute mania▲0▼×

Immediate-release: 300 mg PO TID; increase by 300 mg/day every 2-3 days, guided by serum levels.

Extended-release (Lithobid): 450-900 mg PO once daily or BID; titrate to levels.

Target serum level for acute mania: 0.8-1.2 mEq/L (trough, drawn 12 hours post-dose). Some patients require levels up to 1.2-1.5 mEq/L for acute mania control; above 1.5 mEq/L, toxicity risk increases substantially.

Acute mania usually requires co-treatment with a neuroleptic and/or benzodiazepine while lithium is titrated; lithium does not produce immediate mood stabilization and typically takes 5-14 days to demonstrate full therapeutic effect.

Maintenance prophylaxis▲0▼×

Target serum level for maintenance: 0.6-0.8 mEq/L (minimum effective prophylactic level for most patients). Lower targets (0.4-0.6 mEq/L) can be considered in elderly patients and those with significant adverse effects at higher levels, accepting somewhat higher relapse risk. All levels are 12-hour post-dose troughs. Level timing is critical: drawing at a different interval from 12 hours significantly misinterprets results. Instruct patients to take the evening dose as usual, not take the morning dose, and come for blood draw at a consistent time after the prior evening's dose.

Treatment-resistant depression augmentation▲0▼×

Typical target level: 0.6-0.8 mEq/L (same as bipolar maintenance). Lower levels (0.4-0.6 mEq/L) may be tried in patients intolerant of higher levels. Clinical response assessment at 2-6 weeks at target level; discontinue augmentation if no response at adequate level after 6-8 weeks.

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Effects

• Tremor👤 no reports yet⚕️ no reports yetRate×

  Fine tremor of the hands; the most common adverse effect; occurs in approximately 25-50% of patients. Dose-related; often improves at lower lithium levels. Treated with low-dose propranolol (10-20 mg BID or PRN) or atenolol when bothersome. Must be distinguished from coarse tremor, which is a sign of toxicity.
• <effect>: unknown ref "polyuria-polydipsia"
• <effect>: unknown ref "hypothyroidism"
• <effect>: unknown ref "hyperparathyroidism-hypercalcemia"
• <effect>: unknown ref "cognitive-memory"
• Weight gain👤 no reports yet⚕️ no reports yetRate×

  Common; multifactorial (increased appetite, fluid retention, hypothyroidism contribution). Average weight gain 3-7 kg over the first 1-2 years; highly variable. Address metabolic effects proactively.
• <effect>: unknown ref "gi-effects"
• <effect>: unknown ref "acne-psoriasis"
• <effect>: unknown ref "renal-tubular-disease"
• <effect>: unknown ref "toxicity-early"
• <effect>: unknown ref "toxicity-severe"
• <effect>: unknown ref "edema"

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Pharmacokinetics

Absorption

Essentially complete (approximately 100%) from the GI tract for both lithium carbonate and lithium citrate formulations; lithium is a simple inorganic ion without complex absorption barriers or first-pass metabolism. Immediate-release peak plasma at 1-2 hours; extended-release (Lithobid) peak at 4-6 hours with substantially reduced Cmax (30-40% lower peak than immediate-release at equivalent doses). Food does not significantly affect total absorption.

Distribution

Volume of distribution approximately 0.7-1.0 L/kg; distributes throughout total body water. Unlike most psychotropics, lithium is NOT protein-bound (essentially 0% protein binding -- it is a free ion). Distributes into brain, bone, and most tissues. Does not cross the blood-brain barrier as rapidly as many psychotropics; brain concentrations generally parallel plasma with a slight delay. Crosses the placenta; crosses into breast milk.

Metabolism

None. Lithium is an inorganic ion and undergoes no hepatic or extrahepatic biotransformation. This is a defining pharmacokinetic feature: unlike virtually all other psychotropic medicines, lithium has no CYP450 interactions as a substrate. The therapeutic consequence is that lithium's clearance is entirely a function of renal handling (glomerular filtration rate), and any condition affecting GFR or renal tubular function directly affects lithium levels. There are no active metabolites; all systemic lithium is the parent ion.

Elimination

Exclusively renal. Lithium is freely filtered at the glomerulus and approximately 80% is reabsorbed in the proximal convoluted tubule, in direct competition with sodium. The remaining 20% is excreted in urine. This renal handling mechanism is the key to understanding lithium's interactions and toxicity:

The sodium-lithium competition rule: Sodium and lithium are co-transported in the proximal tubule. When the body is sodium-depleted or volume-contracted (low-salt diet, dehydration, diuretics, ACE inhibitor/ARB use, heavy sweating, vomiting/diarrhea), the kidney increases sodium reabsorption in the proximal tubule -- and lithium reabsorption increases proportionally. This reduces lithium clearance and raises serum levels, potentially to toxic concentrations, without any change in lithium dose. This single mechanism explains the majority of lithium's clinically important interactions.

Half-life 18-36 hours (normal renal function); up to 24-60 hours in elderly and renally impaired patients. Requires 5 half-lives (4-8 days) to reach steady state after a dose change, which is why level checks should not be performed until steady state.

Pharmacodynamics

Lithium exerts its stabilizing effects through multiple intracellular second-messenger and kinase pathways (see mechanism field). At the cellular level, the consequence of GSK-3β inhibition and inositol depletion is modulation of neuronal excitability and activity-dependent signaling rather than a simple receptor agonist or antagonist profile, which explains why lithium has no standard receptor-binding "target" comparable to other psychiatric medicines.

Therapeutic drug monitoring is essential: there is a clear concentration-response relationship for both therapeutic effects and toxicity. The therapeutic window is narrow: - Below 0.6 mEq/L: insufficient prophylaxis for most patients - 0.6-1.2 mEq/L: therapeutic range (maintenance to acute mania) - Above 1.5 mEq/L: early toxicity threshold - Above 2.0 mEq/L: serious toxicity, neurological effects

Lithium level interpretation requires standardized 12-hour trough sampling; levels drawn at other intervals cannot be reliably compared to therapeutic range references calibrated to 12-hour trough values.

Interactions

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Lithium's interaction profile is dominated by its renal elimination and sodium-competition mechanism. Most clinically significant interactions involve medicines that alter sodium balance or renal function:

• NSAIDs (ibuprofen, naproxen, indomethacin, etc.). NSAIDs reduce renal prostaglandin synthesis, decrease renal blood flow, and reduce lithium clearance; serum lithium levels can increase 25-50% with NSAID use. Ibuprofen and naproxen are commonly used OTC medicines that patients may take without informing their prescriber. Counsel patients explicitly not to use NSAIDs without prescriber consultation. Aspirin at low cardiovascular doses is generally acceptable. Acetaminophen is safe.

• Thiazide diuretics (hydrochlorothiazide, chlorothiazide). MOST DANGEROUS diuretic interaction. Thiazides block sodium reabsorption in the distal tubule, causing compensatory increased proximal tubular sodium AND lithium reabsorption; lithium levels can rise 30-50% within days of starting a thiazide. If a thiazide is added for hypertension or edema, reduce lithium dose preemptively, monitor levels frequently, and adjust as needed.

• Loop diuretics (furosemide, bumetanide). Similar mechanism but generally a somewhat smaller magnitude interaction than thiazides; still clinically significant. Monitor lithium levels.

• ACE inhibitors (lisinopril, enalapril, ramipril, etc.) and ARBs (losartan, valsartan, etc.). Reduce angiotensin II and aldosterone, causing sodium wasting, triggering compensatory proximal tubular lithium reabsorption. Lithium levels can rise substantially (20-50%+) when ACE inhibitors or ARBs are started. This interaction is common in clinical practice (hypertension is prevalent in the bipolar population); lithium must be monitored and often dose-reduced when these medicines are added or started.

• Low-sodium diet and dehydration. Dietary sodium restriction activates the same proximal tubular reabsorption mechanism. Counsel patients to maintain consistent sodium intake (not low-salt diets) and adequate hydration. Heavy exercise causing sweating, febrile illness with reduced fluid intake, or GI illness with vomiting/diarrhea are common precipitants of lithium toxicity.

• Amiloride (potassium-sparing diuretic). An exception to the diuretic pattern: amiloride blocks ENaC channels in the collecting duct, which are the entry point for lithium (causing polyuria). Amiloride thus reduces lithium-induced polyuria WITHOUT significantly increasing lithium levels. Preferred treatment for lithium-induced nephrogenic diabetes insipidus when pharmacotherapy is needed.

• Theophylline. Increases renal lithium excretion and can lower lithium levels; dose adjustment may be needed if theophylline is started or stopped.

• Metronidazole. May reduce lithium excretion; monitor levels during courses of metronidazole.

• SSRIs. Combined with lithium's probable serotonergic effects, there are case reports of serotonin syndrome; more commonly used as a beneficial combination for treatment-resistant depression. The risk of serotonin syndrome is low at standard doses but present; monitor for serotonin syndrome symptoms.

• Carbamazepine. Pharmacokinetic interaction: both affect each other's levels; combined neurotoxicity has been reported at plasma levels of each within the therapeutic range. Use with monitoring and clinical vigilance.

• Haloperidol. Historical concern about lithium-haloperidol neurotoxicity reported in a 1974 case series (irreversible encephalopathy at levels within the therapeutic range for both agents).^{[citation needed]} Subsequent evidence suggests this combination is generally safe with monitoring at standard doses. The combination is common in acute mania management.

• Calcium channel blockers (verapamil, diltiazem). May increase lithium levels and enhance neurotoxicity; case reports; monitor.

  Pregnancy and lactation

Lithium's teratogenic risk was dramatically overestimated for decades based on a 1975 voluntary registry report (International Register of Lithium Babies) that found a markedly elevated rate of Ebstein's anomaly (a congenital tricuspid valve malformation). The voluntary-registry methodology introduced severe ascertainment bias: clinicians were more likely to report adverse outcomes, inflating the apparent risk.

Population-based studies have substantially revised the risk downward: - The 2017 NEJM study by Patorno et al (the largest and most rigorous to date) analyzed 1.3 million pregnancies in the US Medicaid database. First-trimester lithium exposure was associated with a relative risk of cardiac malformations of approximately 1.65 (95% CI 1.02-2.68) and Ebstein's anomaly specifically: 14 cases per 10,000 lithium-exposed pregnancies versus 1.5 per 10,000 unexposed pregnancies. In absolute terms, the risk of Ebstein's anomaly is low: approximately 0.14% (14 in 10,000) vs 0.015% background. - The risk is dose-dependent: higher lithium doses and higher first-trimester levels are associated with greater cardiac malformation risk - Neonatal effects: neonatal lithium toxicity ("floppy infant," cyanosis, cardiac arrhythmias, neonatal hypotonia) occurs at the time of delivery due to the neonate's abruptly reduced lithium elimination (the placental clearance is lost); taper dose at term or accept that neonatal monitoring will be needed

Current guidance (integrating the Patorno 2017 data): 1. Lithium should NOT be categorically contraindicated in pregnancy; the risk is real but modest and may be outweighed by the risk of untreated bipolar disorder (psychosis, suicidal behavior, poor prenatal care, postpartum psychosis) 2. Counsel on the absolute risk: ~14 in 10,000 for Ebstein's anomaly vs 1.5 in 10,000 background; overall cardiac malformation risk increases approximately 1.5-2x over background 3. If lithium is continued in the first trimester: offer high-resolution fetal echocardiography at 16-20 weeks 4. Serum lithium levels require more frequent monitoring during pregnancy (GFR increases by 50% during pregnancy, requiring higher doses to maintain target levels; then drops precipitously at delivery, requiring rapid dose reduction) 5. Decision to continue vs switch to an alternative mood stabilizer (valproate is teratogenic [neural tube defects] and generally avoided in pregnancy; lamotrigine or quetiapine are common alternatives with better pregnancy safety profiles) requires individualized counseling

Breastfeeding: Lithium transfers substantially into breast milk (M/P ratio approximately 0.3-0.5); infant serum levels are approximately 10-50% of maternal levels. Neonatal lithium monitoring and renal/thyroid assessment are needed if breastfeeding is continued. Many guidelines recommend against breastfeeding while on lithium due to infant renal elimination immaturity; some maternal-fetal medicine authorities accept it with monitoring in stable patients. Individualized decision.^{[citation needed]}

Monitoring

Lithium has among the most demanding monitoring requirements of any psychotropic medicine, necessitated by its narrow therapeutic index and multisystem adverse effects.

Serum lithium levels (mandatory, cornerstone of management): - Always 12-hour trough (post-dose): draw blood 12 hours after the last dose; evening dose, morning blood draw without taking the morning dose - Initiation: every 5-7 days until two consecutive levels are in target range and dose is stable - Stable maintenance: every 3-6 months minimum; monthly preferred in the first year - After any dose change, addition of interacting medicine, change in sodium intake, intercurrent illness, or renal function change: repeat level within 5-7 days (approximately one full steady state) - Target ranges: maintenance 0.6-0.8 mEq/L; acute mania 0.8-1.2 mEq/L

Renal function (highest-priority long-term monitor): - Serum creatinine, eGFR, BUN at baseline - Every 6 months during first 3 years; every 6-12 months thereafter - If eGFR falls below 60 mL/min: increase monitoring frequency; nephrology consultation - Urinalysis and spot urine osmolality if nephrogenic DI is suspected

Thyroid: - TSH at baseline + at 6 months + every 6-12 months - More frequently if hypothyroid symptoms develop or TSH is borderline

Calcium / parathyroid: - Serum calcium annually; PTH if hypercalcemia detected

Cardiac: - ECG at baseline in patients over 50 or with cardiac history; lithium can cause T-wave changes (usually benign) and rare sinus node dysfunction - Repeat ECG if symptoms develop

Pregnancy-specific (see pregnancy_details): - More frequent serum lithium levels throughout pregnancy (increased GFR alters levels) - High-resolution fetal echocardiography at 16-20 weeks if first-trimester exposure occurred

- Rapid dose reduction / extra monitoring at delivery (precipitous GFR drop at delivery raises lithium levels)

Patient counseling

Blood test timing. Your lithium level must be drawn exactly 12 hours after your last dose -- no earlier, no later. Take your evening dose, skip the morning dose, and get your blood drawn first thing in the morning. An incorrectly timed level will give a wrong result and lead to incorrect dose adjustments.

Salt and fluids. Lithium and salt work together in your kidneys. Do NOT restrict your salt intake. If you sweat heavily, are sick with vomiting or diarrhea, or are in a hot climate, drink extra fluids and replace salt. Any condition that dehydrates you can raise your lithium to dangerous levels.

Medicines to avoid or discuss. Several common medicines raise lithium to toxic levels: ibuprofen (Advil, Motrin), naproxen (Aleve), and other anti-inflammatory painkillers. Use acetaminophen (Tylenol) for pain instead. Also, if you are prescribed a water pill (diuretic) or blood pressure medicine (especially ACE inhibitors or ARBs), tell your prescriber you are on lithium -- those medicines can significantly raise your lithium level.

Signs of toxicity. If you develop nausea, vomiting, diarrhea, coarse shaking, confusion, trouble walking, or slurred speech, STOP taking lithium and go to an emergency room for a lithium level. Do not wait for the next scheduled appointment. Early toxicity is reversible; late toxicity can cause permanent brain damage.

Tremor. Fine trembling of your hands is common and usually not dangerous. Tell your prescriber -- there are medicines that effectively treat this. A coarse, uncontrolled tremor is different and is a toxicity warning sign.

Thyroid and kidney checks. We will check your thyroid and kidney function regularly because lithium can affect both over time. Unexplained fatigue, cold intolerance, or weight gain may indicate thyroid effects; let us know.

Pregnancy. If you are pregnant or planning a pregnancy, discuss this with your prescriber right away. Lithium can cause a small but real increase in heart malformations in the baby if taken in the first trimester. The risk can be monitored with ultrasound. The decision to continue or switch is individualized -- stopping lithium in pregnancy also carries serious risks.

Do not stop suddenly. Stopping lithium abruptly increases the risk of a severe manic or depressive episode and may result in a rebound pattern where episodes become more frequent. If you need to stop, work with your prescriber to taper gradually.

Consistency. Take lithium at the same time every day. Irregular dosing causes erratic levels and reduces effectiveness.

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See also

Valproate, Lamotrigine, Quetiapine, Carbamazepine, Aripiprazole, Bipolar disorder

References

Summary

Classes

Mood stabilizer, Antimanic agent, Narrow therapeutic index medicine

Common uses

• Bipolar I Disorder★★★★★★★★★★★★★★★—×
• Bipolar II Disorder★★★★★★★★★★★★★★★—×
• Bipolar Disorder★★★★★★★★★★★★★★★—×
• Treatment-resistant depression (augmentation)★★★★★★★★★★★★★★★—×
• Cluster headache★★★★★★★★★★★★★★★—×

+ 1 more use →

Pharmacy

Starting dose

Acute mania: 300 mg PO TID (immediate-release) or 900 mg PO once daily (extended-release Lithobid); titrate based on serum levels to target 0.8-1.2 mEq/L. Maintenance: target 0.6-0.8 mEq/L. All dosing guided by serum lithium levels drawn at the 12-hour post-dose standardized trough.

Preparations

Lithium carbonate 150/300/600 mg capsules and tablets (immediate-release; multiple generics); Lithobid 300 mg and 450 mg extended-release tablets; Lithium citrate solution 8 mEq/5 mL (for patients who cannot swallow tablets). Lithium carbonate and lithium citrate are both salts of Li+ and are clinically interchangeable on a molar-equivalent basis.

US FDA Max

No specific labeled maximum dose; dosing is governed by serum lithium levels. Clinical practice targets the minimum effective level for the indication; doses above what achieves target levels confer no benefit and increase toxicity risk. Extended-release Lithobid doses above 1800 mg/day are uncommon in practice.

Pharmacology

Routes

Oral only. No parenteral lithium formulation exists for clinical use.

Onset

Oral peak plasma 1-2 hours (immediate-release); 4-6 hours (extended-release). Therapeutic antimanic effect typically evident within 5-14 days of achieving target serum levels; for acute mania, a neuroleptic or benzodiazepine is usually co-administered while lithium titration proceeds.

Duration

Lithium's mood-stabilizing benefit is prophylactic and requires continuous maintenance dosing; it is not a PRN or acute-episode-only medicine. Discontinuation is associated with high relapse rates and a potentially rebound worsening of episode frequency.

Half-life

18-36 hours at steady state; longer in elderly patients (24-60 hours) and those with renal impairment. Half-life is entirely a function of glomerular filtration rate, as lithium is exclusively renally eliminated with no hepatic metabolism.

Bioavailability

Approximately 100% for immediate-release formulations (lithium is a simple inorganic ion absorbed completely from the GI tract; no significant first-pass effect). Extended-release Lithobid has similar overall bioavailability but a lower and later peak (lower Cmax, longer Tmax), which reduces peak-related adverse effects.

Pregnancy

Teratogenic risk has been substantially revised downward from early (1975 registry) estimates. First-trimester exposure carries a small but real increased risk of cardiac malformations (particularly Ebstein's anomaly, atrioventricular septal defects). The absolute risk increase is modest; informed consent and high-resolution fetal echocardiography are required rather than automatic contraindication. See pregnancy_details for detailed risk-benefit framework.

Legal status

Rx-only. Not scheduled; no abuse potential. One of the oldest continually-used psychotropic medicines, with FDA approval dating to 1970.

Purported mechanism

Lithium's mood-stabilizing mechanism is incompletely understood; it is the only psychotropic medicine in widespread clinical use whose primary therapeutic mechanism remains genuinely uncertain after seven decades of investigation. Multiple intracellular mechanisms have been identified:

GSK-3β inhibition: Lithium is a direct inhibitor of glycogen synthase kinase 3-beta (GSK-3β), competing with Mg2+ at the kinase active site. GSK-3β phosphorylates numerous substrates relevant to mood regulation, neurogenesis, apoptosis, and circadian rhythm (including components of the molecular clock, CLOCK and BMAL1). GSK-3β inhibition is currently considered the most mechanistically important of lithium's intracellular effects and is the basis for lithium's neuroprotective and possibly anti-suicidal properties.^{[citation needed]}

Inositol depletion: Lithium inhibits inositol monophosphatase (IMPase) and inositol polyphosphate 1-phosphatase (IPPase), reducing the recycling of inositol and depleting the inositol pool available for phosphatidylinositol (PI) signaling. The inositol depletion hypothesis (Berridge, 1989) proposes that this selectively dampens PI/protein kinase C (PKC) signaling in neurons firing at high frequency (as in mania), producing a homeostatic dampening effect.^{[citation needed]}

BDNF and neuroprotection: Lithium increases BDNF expression and activates Akt/mTOR neuroprotective signaling. Clinical MRI studies suggest lithium increases cortical gray matter volume in bipolar patients; whether this reflects neuroprotection, neurogenesis, or other mechanisms is debated.

Beta-arrestin pathway (D2 receptor): More recent work suggests lithium may produce biased signaling at dopamine D2 receptors via beta-arrestin pathways, selectively modulating behavioral responses without the typical adverse effects of D2 antagonists.

None of these mechanisms is sufficient alone to explain the full clinical profile. Lithium likely achieves mood stabilization through convergent effects on multiple intracellular kinase cascades and second-messenger systems.▲0▼