Mood Stabiliser (Sodium Channel Blocker) — Bipolar Depression Pregnancy: SPC §4.6: data from more than 12,700 lamotrigine-monotherapy pregnancies do not indicate an increased risk of major congenital malformations at maintenance doses; EURAP data showed a statistically significant increase in major congenital malformations at doses ≥325 mg/day versus <325 mg/day (OR 1.68, 95% CI 1.01–2.80), so if treatment is necessary in pregnancy the lowest possible therapeutic dose is recommended. Folic acid supplementation is recommended when planning and in early pregnancy. Lamotrigine levels may fall during pregnancy (risk of loss of seizure control) and rise rapidly after birth — monitor serum concentrations before, during and after pregnancy and shortly after birth. Lactation: passes into breast milk in highly variable concentrations, giving infant levels of up to about 50% of maternal levels.

Lamotrigine (Psychiatric Use)

Brand names: Lamictal

This page covers lamotrigine in its psychiatric role, where it is used for the prevention of depressive episodes in bipolar disorder rather than primarily as an anticonvulsant.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Bipolar disorder, adults ≥18 years — monotherapy (or adjunctive therapy WITHOUT valproate and WITHOUT glucuronidation inducers): 25 mg/day in weeks 1+2, 50 mg/day in weeks 3+4, 100 mg/day in week 5, then target stabilisation dose 200 mg/day from week 6

Route: Oral (tablets swallowed whole; chewable/dispersible tablets may be chewed, dispersed in water or swallowed whole)

Frequency: Once daily or in two divided doses

Max: Doses in the range 100–400 mg/day were used in clinical trials; target stabilisation dose is 200 mg/day and alters with clinical response

SPC §4.2, Table 3 (bipolar disorder, adults ≥18 years). Because of the risk of rash, the initial dose and subsequent dose escalation must not be exceeded. ADJUNCTIVE WITH VALPROATE: 12.5 mg/day (given as 25 mg on alternate days) weeks 1+2 → 25 mg/day weeks 3+4 → 50 mg/day week 5 → target 100 mg/day week 6; maximum 200 mg/day depending on clinical response. ADJUNCTIVE WITHOUT valproate but WITH inducers of lamotrigine glucuronidation (phenytoin, carbamazepine, phenobarbitone, primidone, rifampicin, lopinavir/ritonavir): 50 mg/day weeks 1+2 → 100 mg/day (two divided doses) weeks 3+4 → 200 mg/day (two divided doses) week 5 → 300 mg/day week 6, increasing if necessary to usual target 400 mg/day in week 7 (two divided doses). If the pharmacokinetic interaction of a co-prescribed medicine is not known, use the regimen recommended for concurrent valproate. WITHDRAWAL of concomitant drugs (Table 4): when valproate is withdrawn, double the stabilisation dose, not exceeding an increase of more than 100 mg/week (100 mg/day → 200 mg/day; 200 mg/day → 300 mg/day week 1, 400 mg/day week 2 onwards). When glucuronidation inducers are withdrawn: from 400 mg/day → 400, 300, then 200 mg/day; from 300 mg/day → 300, 225, then 150 mg/day; from 200 mg/day → 200, 150, then 100 mg/day. ADDITION of drugs (Table 5): adding valproate — halve the dose (200→100, 300→150, 400→200 mg/day); adding inducers without valproate — 200 mg/day → 200/150/100; 300 mg/day → 300/225/150; 400 mg/day → 400/300/200 over weeks 1/2/3 onwards. RESTARTING: reassess the need for escalation to maintenance dose; if the interval since discontinuation exceeds five half-lives, re-escalate according to the appropriate schedule. Do not restart in patients who discontinued because of rash unless the potential benefit clearly outweighs the risk. DISCONTINUATION in bipolar disorder: patients may stop without a step-wise dose reduction (no increase in adverse reactions on abrupt termination vs placebo in trials). HORMONAL CONTRACEPTIVES: ethinyloestradiol/levonorgestrel (30 µg/150 µg) roughly doubles lamotrigine clearance — maintenance dose usually needs to be increased by up to two-fold, raised by 50–100 mg/day each week; on stopping, decrease by up to 50%, reducing by 50–100 mg/week (not exceeding 25% of total daily dose per week) over 3 weeks. CHILDREN/ADOLESCENTS <18 YEARS: Lamictal is NOT recommended for bipolar disorder in patients under 18 — a randomised withdrawal study showed no significant efficacy and increased reporting of suicidality. (Epilepsy dosing is a separate indication — see the epilepsy entry.)

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients

Side effects

Very common: headache; skin rash
Common: somnolence, dizziness, tremor, insomnia, agitation; aggression, irritability; nausea, vomiting, diarrhoea, dry mouth; arthralgia, back pain, pain, tiredness
Uncommon: ataxia, diplopia, blurred vision, alopecia, photosensitivity reaction
Rare/very rare: Stevens–Johnson syndrome, erythema multiforme, toxic epidermal necrolysis, DRESS/hypersensitivity syndrome, aseptic meningitis, haemophagocytic lymphohistiocytosis
Very rare: haematological abnormalities (neutropenia, leucopenia, anaemia, thrombocytopenia, pancytopenia, aplastic anaemia, agranulocytosis), hepatic failure/hepatic dysfunction, lupus-like reactions, confusion, hallucinations, tics

Interactions

Valproate — inhibits lamotrigine glucuronidation; use the reduced valproate escalation schedule (halve maintenance dose if valproate is added) and note the increased risk of serious rash
Inducers of lamotrigine glucuronidation: phenytoin, carbamazepine, phenobarbitone, primidone, rifampicin, lopinavir/ritonavir — use the higher escalation schedule; adjust dose when they are added or withdrawn
Oestrogen-containing hormonal contraceptives (e.g. ethinyloestradiol/levonorgestrel 30 µg/150 µg) — approximately double lamotrigine clearance; maintenance dose usually needs increasing up to two-fold, and reducing by up to 50% on stopping. Consider contraception without a pill-free week
Other oestrogen-containing therapies including HRT — may interfere with lamotrigine; monitor effectiveness and consider level measurement
Atazanavir/ritonavir — no change to escalation when lamotrigine is added to existing therapy, but the lamotrigine dose may need increasing if atazanavir/ritonavir is added or decreasing if stopped; monitor plasma levels before and for 2 weeks after starting/stopping
US label §7: strong or moderate CYP3A4 inducers, which also induce UGT, may enhance lamotrigine metabolism

Clinical monograph

How it works

Lamotrigine inhibits voltage-gated sodium channels and stabilises neuronal membranes, modulating release of excitatory neurotransmitters, which is thought to underpin its mood-stabilising effect.

Prescribing in practice

Serious skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis can occur, so the dose must be titrated slowly from a low starting dose and any rash, especially with systemic or mucosal involvement, prompts urgent review and usually withdrawal.
Rapid escalation and interactions markedly affect risk: valproate raises lamotrigine levels (slower titration needed) while enzyme inducers and some hormonal contraceptives lower them, requiring dose adjustment.
Counsel on hypersensitivity syndrome and the need to seek help for fever, swelling or blistering, and re-titrate from low dose if treatment has been interrupted.

Monitoring

Monitor for skin reactions and hypersensitivity, mood response and the impact of interacting drugs and any treatment interruption on dosing.

Counselling the patient

Report any rash, blistering, mouth ulcers or fever urgently, particularly in the first weeks.
Take exactly as titrated and never increase the dose faster than instructed.
Tell your clinician about contraceptive changes, as these can alter the dose needed.

Evidence & guidelines

NICE bipolar disorder guidance supports lamotrigine for preventing bipolar depression, and product information emphasises slow titration to reduce serious rash risk.

Reference: NICE CG185 (Bipolar Disorder); MHRA Lamotrigine Safety Update; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways