What happens when you take lamotrigine with folate?
Lamotrigine is a widely used anticonvulsant and mood stabilizer. Folate (vitamin B9) is found in food and in many supplements and prenatal vitamins as folic acid. For most people the two coexist without trouble, but in one specific situation, treating bipolar depression with lamotrigine, adding extra folic acid has been linked to a weaker response to the drug.
- Lamotrigine works on mood and seizure pathways. It stabilizes electrical activity in the brain and, in bipolar disorder, helps hold off depressive episodes.
- Extra folic acid is added on top. People often start a prenatal vitamin, B-complex, or standalone folic acid supplement for unrelated reasons, assuming a B-vitamin is harmless.
- In bipolar depression, the antidepressant benefit appeared to fade. In a randomized trial, people taking lamotrigine plus folic acid did worse on mood than those taking lamotrigine plus a placebo supplement.
- Lamotrigine blood levels did not change. The drug was still absorbed and present at normal concentrations, so the interference happens at the level of the body's response, not the drug level.
- The exact reason is unclear. Lamotrigine is a weak inhibitor of an enzyme (dihydrofolate reductase) involved in folate processing, which is a plausible thread, but the trial investigators could not pin down the mechanism. The effect was strongest in people carrying a particular gene variant (the COMT Met allele).
So the honest summary is: there is a real but modest signal in bipolar depression, and we do not fully understand why it happens.
Why is this important?
This interaction is easy to overlook for two reasons. First, lamotrigine blood levels stay normal, so routine drug-level monitoring will not flag anything. Second, folic acid sits inside vitamins that almost everyone assumes are completely safe, so neither patient nor prescriber tends to suspect it.
For people with bipolar disorder who depend on lamotrigine to keep depressive episodes at bay, a blunted response can mean a preventable dip in mood or a relapse, with no obvious lab finding to explain it. Catching the timing, mood worsening after a new vitamin was started, is often the only clue.
For people taking lamotrigine for epilepsy, this concern does not translate directly. The trial evidence is specific to bipolar depression, and there is no good evidence that ordinary folate supplementation worsens seizure control. The caution here is much softer.
There is also a genuine tradeoff for women of reproductive age. Folate substantially lowers the risk of neural tube defects in pregnancy, and that benefit clearly outweighs a modest, uncertain mood signal. The right approach during pregnancy planning is a clinical decision, not something to settle from a supplement label.
What should you do?
Before changing anything: Make a list of every supplement you take, prenatal vitamins, B-complex products, and standalone folic acid all count, and check whether any of them add folic acid on top of your diet. Bring this list to your prescriber or pharmacist rather than adjusting things on your own.
Day to day: A standard multivitamin level of folate, plus folate from food (leafy greens, beans, fortified grains), has no documented problem with lamotrigine. If you are not pregnant or planning pregnancy, there is usually no need to add a separate high-strength folic acid supplement unless your prescriber asked for it.
After any change: If you start a new vitamin and your lamotrigine seems to "stop working" for mood over the following weeks, tell your prescriber and mention the timing. This is fixable if caught early. If you genuinely need more folate, ask whether folinic acid (leucovorin) or methylfolate would be a better fit, since these forms bypass the enzyme step lamotrigine partially inhibits. And if you are pregnant or planning pregnancy, do not stop folate on your own, let your medical team set the dose.
Which specific products are affected?
Lamotrigine is sold under the brand name Lamictal and in many generic versions, including extended-release (Lamictal XR) and orally disintegrating (Lamictal ODT) forms. The folate question applies the same way across all of them.
On the folate side, the products worth reviewing with your prescriber are:
- Standalone folic acid supplements and prescription folic acid tablets
- Prenatal vitamins (most contain a meaningful folic acid dose)
- B-complex supplements that include folic acid
- Fortified "medical foods" marketed for mood that contain L-methylfolate
Everyday multivitamins with a modest folate amount, and folate from food, are not the concern here. The signal comes specifically from adding extra supplemental folic acid on top of lamotrigine in bipolar depression.
The science behind it
The clearest evidence comes from the CEQUEL randomized controlled trial (Geddes and colleagues, Lancet Psychiatry, 2016), which tested lamotrigine with folic acid against lamotrigine with placebo in people with bipolar depression. Adding folic acid did not help and appeared to reduce lamotrigine's antidepressant benefit over 12 weeks, a surprising result, since folate had been expected to help.
A later secondary analysis of the same trial (Tunbridge and colleagues, Bipolar Disorders, 2017, PMID 28833962) looked at who was affected and why. The blunting effect was concentrated in people carrying the COMT Met allele, but the authors were explicit that they could not establish the mechanism. Lamotrigine's labeling does note that it is a weak inhibitor of dihydrofolate reductase, an enzyme in folate metabolism, which offers a plausible but unproven link.
Two honest caveats: the folic acid in the trial was given on a background of another mood medication (quetiapine), and the finding has not been widely replicated. So this is a real, trial-grade signal, but a specific and incompletely understood one, not a sweeping rule about folate and lamotrigine.
Frequently Asked Questions
Do I need to stop taking folate if I'm on lamotrigine?
No. A standard multivitamin level of folate and folate from food are not a documented problem. The concern is specifically about adding extra high-strength folic acid on top, and even then mainly in bipolar depression. Talk to your prescriber before changing anything.
Does this affect lamotrigine for epilepsy?
The trial evidence is specific to bipolar depression. There is no good evidence that ordinary folate supplementation worsens seizure control, so the caution is much softer for epilepsy.
Will this change my lamotrigine blood level?
No. In the trial, lamotrigine levels stayed normal. That is part of why the interaction is easy to miss, routine blood monitoring will not catch it.
I'm pregnant or planning pregnancy. Should I stop folate?
No, do not stop on your own. Folate substantially lowers the risk of neural tube defects, and that benefit outweighs the modest, uncertain mood signal. Let your medical team set the right dose.
Is methylfolate or folinic acid safer with lamotrigine?
They are reasonable alternatives if you genuinely need more folate, because they bypass the enzyme step lamotrigine partially inhibits. Discuss the choice with your prescriber rather than switching on your own.
How would I know if this is happening to me?
The main clue is timing: a worsening of mood in the weeks after starting a new vitamin, while your lamotrigine dose is unchanged. Mention that timing to your prescriber.
Key takeaways
- The evidence for a lamotrigine–folate clash comes from one randomized trial in bipolar depression, where added folic acid appeared to blunt lamotrigine's antidepressant benefit.
- The mechanism is not established; the trial authors could not explain it, so avoid treating the enzyme story as settled fact.
- Lamotrigine blood levels stay normal, so lab monitoring will not catch this, watch the timing of new vitamins instead.
- A standard multivitamin level of folate and dietary folate are not the concern; extra high-strength folic acid is.
- For epilepsy the concern is much weaker, and pregnancy planning overrides it entirely, handle that with your medical team.