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L-Theanine
An amino acid found naturally in tea, which our formulators pair with caffeine in the morning and with melatonin and magnesium at night. It carries no authorised EU claim: EFSA looked at the claims put forward for it on cognitive function and mental stress and turned them down. It sits in two formulas, at the same 200 mg in each.
WHAT WE ARE ALLOWED TO SAY
No authorised claim. EFSA looked, and said no.
There is no health claim for L-theanine on the EU register, so there is no wording for us to quote. It is not that nobody asked: in 2011 EFSA assessed claims for cognitive function and for the reduction of mental stress and turned them down. That is why nothing is listed here and why we do not attribute an effect to it.There is no health claim for L-theanine on the EU register. EFSA assessed claims on cognitive function and mental stress in 2011 and turned them down, so we do not attribute an effect to it.
You will read that L-theanine sharpens your focus, lowers your stress or helps you sleep. None of those is an authorised claim. In Sleep & circadian rhythm, the sleep claim comes from the melatonin and the nervous system claims from the magnesium next to it. In Cognitive & focus, the alertness and concentration claim comes from the caffeine, not from the L-theanine.
WHY PURE L-THEANINE
No claim to protect. Only purity.
No form of L-theanine carries an authorised claim, so the form is not a claim argument and we do not use it as one. What we specify is pure L-theanine, at least 98%, which is the form named in the EU regulatory record we hold on file for it. It dissolves in water, stays stable in liquid and tastes neutral, which is what a formula poured in 0.2 ml pulses needs.
L-theanine at a purity of at least 98%. It is the form named in our EU regulatory record for this ingredient, chosen so we know what is in the batch, not for a stronger claim.
Our file names Suntheanine®, made by Taiyo, as the most studied pure form, and accepts generic pure L-theanine as a valid alternative. Our formula records do not yet say which of the two goes into the batch.
It dissolves in water, stays stable in liquid and tastes neutral, so it can be served in small pulses without changing the taste of a formula.
We have no source that says one pure L-theanine is better absorbed than another, and we are not going to imply it. Our ingredient file gives an onset of 30 to 60 minutes and a half-life in the blood of about an hour, citing Scheid 2012 for the half-life; our pharmacokinetic record, which cites no source of its own, puts the onset at about 30 minutes. The purity requirement is about knowing what you are taking, nothing more.We have no source that says one pure L-theanine is better absorbed than another. The purity requirement is about knowing what you are taking, nothing more.
WHERE IT APPEARS
Two of the twenty-nine carry L-theanine.
The same 200 mg in both, doing two different jobs. In the morning it sits next to caffeine at the 2:1 ratio our library recommends; at night it sits next to melatonin and magnesium. 200 mg is the dose our file gives for both focus and sleep, inside the 100 to 400 mg a day used in published work. The two never share a window: the focus formula is never served after 2 pm and the sleep formula is never served in the morning.
THE CEILING
Under review. Our records do not agree.
Our records do not agree on an upper limit for L-theanine, and until they do we will not present either figure as settled. Our ingredient file records no upper intake level set by EFSA, and no NRV; in that file, the 250 mg you may see quoted is a US figure for a single serving, and the ceiling it sets is 400 mg a day across everything you take. Two of our records, the dose table and the EU regulatory record, list 250 mg a day as an EU limit, and our engine currently works to that figure. That matters if your plan carries both formulas: 200 mg in the morning and 200 mg at night make 400 mg, which our engine flags as over the limit. Until the records are reconciled, that flag stands.Our records disagree. Our ingredient file notes no EFSA upper limit and caps your total at 400 mg a day; two other records list 250 mg a day, which is the figure our engine uses. Both formulas together make 400 mg, and the engine flags that.
The cap is on the sum, not on each formula. Our file also flags green tea extracts standardised for L-theanine, and matcha, whose amounts vary, as ways of doubling up without noticing.
Very well tolerated. Reported: an occasional mild headache and a slight drop in blood pressure. No relevant toxicity is documented up to 900 mg a day.
Take care in pregnancy and breastfeeding, where the data are insufficient. Both formulas that carry it are not for use in pregnancy or breastfeeding, nor if you take vitamin K antagonist (VKA) anticoagulants. Cognitive & focus is also not for under-18s or people with heart disease, and is stopped 3 to 4 days before surgery because of the bleeding risk from the ginkgo in it. Sleep & circadian rhythm is also not for people with liver disease or an autoimmune condition. These exclusions come from the formulas and the ingredients next to it: our L-theanine file lists no contraindication for anticoagulants, the heart or the liver. Each formula page explains them. Under 18, our file covers only the amounts found in tea; as a supplement, ask a doctor first. If your blood pressure runs low, or you take blood pressure medication, it can lower it slightly further, so keep an eye on it. No specific warning is legally required on the label for L-theanine; the standard ones apply: do not exceed the recommended daily dose, it is not a substitute for a varied and balanced diet, and keep it out of the reach of young children.
WHAT IT REACTS WITH
Documented pairs, not hunches.
L-theanine is one of the 140 ingredients in our library, so it has 139 possible partners. We have documented 8 of them, out of the 443 pairs on file. Six are complementary: caffeine, magnesium and melatonin, which it shares formulas with, and GABA, L-tyrosine and CBD. Two only need spacing.
The best-documented pair in our library. Our file recommends a 2:1 ratio, 200 mg of L-theanine to 100 mg of caffeine, which is the ratio in Cognitive & focus. We make no claim about what the pairing does.
Charcoal binds it in the gut and is kept at least 2 hours apart. Psyllium husk can slightly reduce how much of it you absorb and is kept at least 1 hour apart.
It can add slightly to the effect of blood pressure medication, and mildly to sedatives and sleeping pills. With stimulant medication such as amphetamine or methylphenidate, the only data on file are preliminary. Our file lists no major drug interaction.
None of L-theanine's medication interactions is in our drug table yet: the warning above comes from its own file, not from a checked pair, and we have found nothing on file about the liver enzymes that process most medicines. Across the library, 443 of the 9,730 possible pairs are documented, which is 4.55%. The rest are not "safe", they are simply unchecked, and we would rather write that down than let the number look like a badge.None of L-theanine's medication interactions is in our drug table yet. Across the library, 443 of the 9,730 possible pairs are documented, which is 4.55%. The rest are not safe, they are simply unchecked.
SOURCES
Everything on this page, with its reference.
Reviewed by VION nutrition team · last reviewed 16 September 2026Read the introduction to Green tea extract (L-theanine) →
140 INGREDIENTS · 64 IN USE TODAY
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What it is, what we are allowed to say about it, which formulas carry it, what it reacts with and where each of those statements comes from. No proprietary blends, no hidden amounts.