This page shows what was measured, who it was measured in, and what that does not settle.
What L-theanine does in the body
Sold for calm alertness.
L-theanine looks enough like glutamate, the brain's main excitatory signal, to be carried into the brain by the same transporter. Once there it interacts weakly with glutamate receptors and shifts the balance toward inhibition, which shows up on an EEG as increased alpha-wave activity — the pattern associated with relaxed wakefulness rather than drowsiness. Paired with caffeine, the combination reliably outperforms caffeine alone on attention tasks in the laboratory.
What happened in people
Combined with caffeine, L-theanine improved attention more than caffeine alone.
✓ Reviewed first-read answer
Where this came from
A person wrote this and a reviewer approved it against this exact record. It carries no effect size.
A reviewer approved this against this record. The reviewed-claim record carrying the exact population and effect size does not exist yet.
No source is stored against this line.
The limit that matters most
Studies of stress or sleep are still too few and too small for firm conclusions.
Where it acts
Central nervous system, entered via the large neutral amino acid transporter
Kind of result
The kind of result is not recorded
Supervision
Not usually supervised: sold as a supplement or food ingredient where recorded. That is a legal category, not a safety judgement.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · 8021PR16QO · read 2026-08-29
The supplement label database classes it as amino acid, under the name Theanine.
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
The limit a reviewer approved as the one that matters most here.
The four opening statements run to 84 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
Enzyme
An enzyme is a protein that speeds up one chemical change.
A picture of it, and where the picture fails
An enzyme is like a machine on a production line doing one cut.
Where that stops being true. A machine is switched on and off by a person. Enzymes are controlled by the cell.
What people get wrong. Enzymes are thought to be used up. They are not; they work again and again.
A catalytic protein that lowers the activation energy of a specific reaction.
Receptor
A receptor is a part of a cell that a signal fits into.
A picture of it, and where the picture fails
A receptor is like a lock waiting for one key.
Where that stops being true. A lock either opens or does not. A receptor can be half-triggered, or worn out.
What people get wrong. Fitting a receptor is read as causing a benefit. It causes a step, and nothing more.
A protein that binds a specific ligand and converts that binding into a cellular response.
Pathway
A pathway is a chain of steps inside a cell, each one setting off the next.
A picture of it, and where the picture fails
A pathway is like a row of dominoes.
Where that stops being true. Dominoes fall one way. Pathways loop back and can switch themselves off.
What people get wrong. Changing one step is read as changing the outcome. Other steps often absorb it.
An ordered series of molecular interactions producing a defined cellular change.
What happened in people◇Read from sources, not yet reviewed
What was measured, goal by goal
One row for each goal a registered study measured something for. One column for each kind of thing that could be measured.
Registered studies list 6 outcome measures that RNAWiki could read. A registered study says what someone planned to measure. It does not say what they found. 0 of the matched studies tested this substance, and 0 posted a result.
There is no single score. A strong test result and a weak life result are different facts.
Goals down the side, kinds of measurement across the top. Each cell says what kind of thing was registered, not what was found.
Goal
Life outcome
What a body can do
How a person feels
A test result
A step in the body
Harms
How long
Who was studied
Focus
∅Nothing in the sources checkedNo registered study lists a life outcome for this goal.
…Waiting for a reviewer1 registered performance measure of this kind.
∅Nothing in the sources checkedNo registered study lists a symptom measure for this goal.
∅Nothing in the sources checkedNo registered study lists a test result for this goal.
∅Nothing in the sources checkedNo registered study lists a body-step measure for this goal.
—Not recordedHarms were not a registered measure for this goal.
—Not recordedNo finished study window is recorded.
…Waiting for a reviewerWho was studied is listed further down the page.
Which registered measures put each goal on this table
Focus
cognitive performance
Sorted by fixed word lists, version v1. A name the rules do not recognise stays unsorted rather than moving to the nearest column.
What each mark on this table means
∅ Nothing in the sources checked
No registered study lists a life outcome for this goal.
… Waiting for a reviewer
1 registered performance measure of this kind.
— Not recorded
Harms were not a registered measure for this goal.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Change in stress-related symptom scales and cognitive function over four weeks
✓ The study showed what it set out to show
Who was studied
Hidese 2019 (200 mg/day L-theanine, four weeks, healthy adults)
P = 0.019 SDS, P = 0.006 STAI-trait, P = 0.013 PSQI, P = 0.001 verbal fluency
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Two authors are employees of the company that supplied both the L-theanine and the placebo tablets. The trial discloses this and it does not invalidate the result, but it belongs beside it.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, tablet or powder; also added to beverages
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Whether a cause and effect relationship is established for cognitive function, psychological stress, normal sleep or menstrual discomfort
✗ The study did not show it
Who was studied
EFSA Article 13(1) assessment of L-theanine health claims
How many people
0
Study design
Regulatory scientific opinion
Compared against
Not recorded for this study
Kind of result
What a body can do day to day
What was found
Not applicable — regulatory assessment, not a hypothesis test
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. Sample size recorded as 0 because this is an evidence assessment rather than a trial. No cause and effect relationship was established for any claim.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, tablet or powder; also added to beverages
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 3 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What happened in people◇Read from sources, not yet reviewed
How close this is to real life
The top step is something a person would feel or care about. The bottom is a guess from software. Filled steps are where evidence exists for this substance.
□Living longer, or avoiding a major eventNo evidence recorded. Death, a heart attack, a stroke, a hospital stay.No registered study measures this.
■What a body can do day to dayEvidence recorded. Walking, dressing, breathing, recovering.1 registered measure of this kind.
■Measured performanceEvidence recorded. How much was lifted, how far was run, how fast.1 registered measure of this kind.
■Symptoms and quality of lifeEvidence recorded. Pain, tiredness, mood, sleep, as the person rated it.3 registered measures of this kind.
□A number that stands in for healthNo evidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.No registered study measures this.
■A step measured inside a personEvidence recorded. Something measured in human tissue or human cells.A human record sits on the stored organism ladder.
■AnimalsEvidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.Stored records in C. elegans (roundworm), Mouse, Rat. A result in animals says what to test next. It does not say what happens in people.
■Cells in a dishEvidence recorded. Cells or chemistry on a bench, far from a whole body.Stored mechanism abstracts describe steps measured in cells or tissue.
□A guess from softwareNo evidence recorded. Nobody measured it. RNAWiki never publishes one as a finding.RNAWiki stores no prediction for this record. Software can suggest a link. RNAWiki does not publish one as a finding.
Higher on these steps means closer to something a person would feel. It does not mean better done.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
L-theanine
What a person takes: Oral capsule, tablet or powder; also added to beverages.
The measurement behind this step
Sold as a dietary supplement, and self-affirmed GRAS for use in beverages in the United States. Industrial material is made enzymatically or by fermentation rather than extracted from tea, so enantiomeric purity is a manufacturing specification rather than a botanical given. Every trial cited here used the L-enantiomer.
Getting in
Absorbed intact from the small intestine
Unlike most compounds in this file, L-theanine is a simple amino acid and the body absorbs it readily.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
L-theanine is absorbed by intestinal amino acid transporters and appears in plasma within roughly 30 minutes, peaking in the first hour or two. This is the pharmacokinetic contrast with curcumin and berberine: absorption is not the limiting problem here.
Carried into the brain on the glutamate lookalike route
Because it resembles a common amino acid, a transporter at the blood-brain barrier carries it across.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Transit is via the large neutral amino acid transporter LAT1, which theanine shares with leucine, phenylalanine and tryptophan. That sharing means central exposure is in principle competitive with dietary amino acids, a variable no clinical trial in this dossier controlled.
In the brain it interacts loosely with the receptors for the main excitatory signal, nudging the balance toward calm.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
L-theanine is a glutamine and glutamate structural analogue with low-affinity activity at AMPA, kainate and NMDA receptors, and it inhibits glutamine transport. The affinities are low enough that the pharmacology remains debated, and no receptor occupancy has been demonstrated in a human brain.
Brain recordings show more of the wave pattern associated with being relaxed but awake.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Increased occipital and parietal alpha-band power under resting conditions is the most consistently reproduced pharmacodynamic marker for L-theanine, and it distinguishes the effect from sedation, which shows a different signature.
With caffeine, attention improves beyond caffeine alone
The practical result is the pairing: sharper focus with less of the edge caffeine brings on its own.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The combination outperformed caffeine alone on attention tasks, and the fMRI follow-up attributed the gain to reduced mind wandering rather than to general arousal. This is the specific, replicated, measurable claim; the broader wellness claims were the ones EFSA rejected.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What it would be like to take◇Read from sources, not yet reviewed
Felt, measured, or meaningful
Three different things that get called the same word. Registered studies measured all three, and mixing them is how a blood test becomes a health claim.
Felt
Things a person could notice without a test.
clinical global impression scale
positive and negative syndrome scale
well being
Measured
Things only a test, a scale or a device shows.
No registered study measured anything of this kind.
Meaningful
Things that change how a life goes, not only a number.
cognitive performance
A registered study says what someone planned to measure. It does not say what they found. A number moving is not the same as a life going better. The two are shown apart here.
Felt, but not shown to help. A person notices a change. No study showed it leads anywhere good.
Measured, but not felt. A number moves. The person notices nothing. Both can be true.
Measured, but not shown to matter. A number moves in the good direction. Nobody showed that lives went better.
Matters, but takes years. The result that counts may take longer than anyone would keep watching.
Names that fit none of the three (2)
scale for the assessment of negative symptoms
alertness
These are harms, study-process measures, or names the rules did not recognise. They are shown rather than dropped.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Adults seeking focus without caffeine jitteriness, people with sleep-onset difficulty, and heavy users of nootropic stacks. It is also added to energy drinks specifically to soften caffeine.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
Where the result stopped carrying
Every L-theanine health claim submitted to EFSA under Article 13(1) — cognition, psychological stress, sleep and menstrual discomfort — failed to establish a cause and effect relationship
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied for a different goal
The studies measured something else entirely.
On this record: Some registered studies measured things that match no goal on this page.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
The product may not be what it says
Contents of a sold product are not always what the label states.
On this record: This is sold as a supplement, so no agency checked what is in a given tub before it was sold.
Other reasons RNAWiki checked and found nothing for (9)
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Varies by country
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral capsule, tablet or powder; also added to beverages
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
Not usually supervised: sold as a supplement or food ingredient where recorded. That is a legal category, not a safety judgement.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
The identity record classes it as a supplement ingredient; no medicines register records an approval.
No source is stored against this line.
What is in the pack
Sold as a dietary supplement, and self-affirmed GRAS for use in beverages in the United States. Industrial material is made enzymatically or by fermentation rather than extracted from tea, so enantiomeric purity is a manufacturing specification rather than a botanical given. Every trial cited here used the L-enantiomer.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold and what that means for what is in the pack.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Among the best-tolerated substances in this file. Adverse events in the trials were minimal and comparable to placebo, and no serious safety signal has emerged. The practical caution is contextual: L-theanine is usually consumed alongside caffeine, and the caffeine is where the cardiovascular and sleep-disruption risk lives.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
These are reports people sent to a regulator. They do not show the medicine caused the reaction.
Nobody counted how many people took the medicine and reported nothing.
The same event can be reported more than once, and many reports are incomplete.
News coverage, lawsuits and new warnings change how often people report.
A count is not a rate and not a risk.
L-theanine appears in spontaneous reports to regulators. Across the 1 most-reported reaction terms, 2 reaction mentions were counted. One report can name several reactions.
The recorded terms (1)
metal poisoning — 2 reaction mentions
open-targets-adr · recorded 2026-06-24 · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral capsule, tablet or powder; also added to beverages
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
Industrial material is made enzymatically or by fermentation rather than extracted from tea, so enantiomeric purity is a manufacturing specification rather than a botanical given. Every trial cited here used the L-enantiomer.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
2101 marketed supplement labels list this ingredient, classed as amino acid/protein, non-nutrient/non-botanical and other combinations.
Those labels carry all other, nutrient and structure/function claims. A claim of that kind is written by the manufacturer and is not assessed by any regulator, so its presence says nothing about whether it is true.
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
Watching one thing carefully can tell you whether it moved. It cannot tell you what moved it.
This is sold without a prescription, so a person can sensibly watch one thing and see whether it moves.
Pick one goal. One goal only. Two at once cannot be told apart afterwards.
Pick one thing to watch. No registered study lists a measure RNAWiki could read for this.
Measure before you start. Take the same measurement several times first. One reading is not a starting point.
Know the swing. Write down how much it moves on its own across a normal week.
Change one thing. Change nothing else at the same time, including training and sleep.
Give it the study length. No finished study window is recorded, so no length is suggested here.
Track whether you took it. Missed days are the most common reason a home test shows nothing.
Read the trend. Look at the line across weeks. A single reading tells you almost nothing.
What not to measure
Anything that swings more day to day than the change you are looking for.
A wearable estimate of sleep stages, which is an estimate and not a measurement.
Weight on one morning, which mostly records water.
A feeling you did not write down before starting, such as: clinical global impression scale.
When to stop
Stop if something new and unpleasant starts, and ask a pharmacist or doctor.
Stop if you cannot keep everything else steady, because the result will not mean anything.
Stop at the end of the window you set, and read the trend then.
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki does not work out an amount for anyone.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That an acute effect on a laboratory attention task supports a package claim about cognitive function, stress or sleep — EFSA assessed exactly that and rejected it
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That results in healthy volunteers under acute stress extend to diagnosed anxiety disorders
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That a supplier-funded 30-person crossover trial settles the chronic-use question
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
How much did people take in the studies?
The sources RNAWiki checked hold nothing for this field.
Why it matters. A result belongs to an amount. Without the amount the result floats free.
What would answer it
A stored source that records it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
How fast does the body clear it?
The sources RNAWiki checked hold nothing for this field.
Why it matters. Without this, nothing on this page can say how long anything lasts.
What would answer it
A stored source that records it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of L-theanine are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Theanine plus caffeine beats caffeine alone on attention
In plain words
In controlled laboratory tests, the combination sharpens attention more than caffeine on its own does.
What was measured
Acute attention task performance and task-related fMRI activation
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Kahathuduwa et al. measured the acute effects of theanine, caffeine and the combination on attention in a within-subject design and found the combination produced the largest improvement. A subsequent functional MRI study by the same group reported that the combination improved target-specific attention to visual stimuli by decreasing mind wandering, with the imaging showing reduced default-mode network activity during the task. Two different measurement modalities pointing the same way is the strongest evidence on this page.
Written into the record, not signed off as a reviewed claim
Four weeks improved sleep-quality and verbal-fluency scores in 30 adults
In plain words
A month of daily L-theanine improved sleep questionnaire scores and two cognitive test scores in a small crossover trial.
What was measured
PSQI, STAI-trait, SDS, verbal fluency and executive function over four weeks
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Hidese et al. ran a randomised, placebo-controlled, crossover, double-blind trial in 30 healthy adults with no major psychiatric illness, giving 200 mg/day L-theanine or placebo for four weeks. Self-rating Depression Scale, State-Trait Anxiety Inventory-trait and Pittsburgh Sleep Quality Index scores all fell after L-theanine (P = 0.019, 0.006 and 0.013). PSQI subscale scores for sleep latency, sleep disturbance and use of sleep medication all reduced against placebo. Verbal fluency and executive function scores improved (P = 0.001 and 0.031). Two of the seven authors are employees of the company that supplied the L-theanine and placebo tablets, which the paper discloses.
Written into the record, not signed off as a reviewed claim
EFSA rejected every health claim submitted for L-theanine
In plain words
Europe's food safety regulator looked at the claims for cognition, stress, sleep and menstrual discomfort and concluded that none of them was supported.
What was measured
That an acute laboratory effect on an attention task supports a package claim about cognitive function, stress or sleep
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The EFSA Panel on Dietetic Products, Nutrition and Allergies assessed L-theanine from Camellia sinensis under Article 13(1) of Regulation (EC) No 1924/2006 across four claim areas: improvement of cognitive function (claim IDs 1104, 1222, 1600, 1601, 1707, 1935, 2004, 2005), alleviation of psychological stress (1598, 1601), maintenance of normal sleep (1222, 1737, 2004) and reduction of menstrual discomfort (1599). No cause and effect relationship was established for any of them. That is a regulatory judgement about whether the evidence supports a claim on a package, not a finding that the laboratory results are wrong.
Written into the record, not signed off as a reviewed claim
The systematic review found the evidence promising and the trial base small
In plain words
A 2020 review concluded L-theanine probably helps with acute stress and that the studies are too few and too small to say more.
What was measured
That an effect in acute laboratory stress paradigms extends to diagnosed anxiety disorders
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Williams et al. reviewed the evidence for L-theanine consumption and the ability to manage stress and anxiety, and found supportive signals across acute-stress paradigms alongside considerable heterogeneity in dose, format and outcome measure, with few trials in clinically anxious populations. The review's value here is as a boundary: the case is for acute, situational stress in healthy people, not for anxiety as a diagnosis.
This order is fixed in code and does not count clicks or time on the page.
What is not here
5 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
How this medicine reached us — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
A tea amino acid with a reproducible acute effect on attention when paired with caffeine, a four-week trial showing better sleep-quality and verbal-fluency scores, an excellent safety record, and a European regulator that rejected every claim made for it.
Recorded evidence blocks (11)
Q1
What did L-theanine's largest trial (100 people) and its longest (2.2 years) measure?
100 people in L-theanine's largest registered study, 2.2 years in its longest registered window, measuring Cognitive performance. ClinicalTrials.gov · 2026-09-01
4 na, 3 early phase1, 1 phase2, 1 phase3, 1 phase4; NCT00372151; 2008-12; no ageing endpoint recorded. Last human test completed 2025, NCT07268573.
Interpretation These counts include studies where L-theanine was a comparison treatment, a background treatment or an exposure in an observational study, and the longest window may be a planned end date. Trial roles have not yet been classified for this record.
Show the evidence
na
4
early phase1
3
phase2
1
phase3
1
phase4
1
Last recorded human testNCT07268573
2025-08-14
recorded 2026-09-01 · last checked 2026-09-04
Q2
From C. elegans to human: where has L-theanine shown lifespan?
"L-Theanine to Support Relaxation and Mood for Cancer Patients in Surveillance"; n 50; "Adherence rates"; 2027-07-09
recorded 2026-09-01 · last checked 2026-09-04
Q7
Which 6 trials of L-theanine posted no result?
Posted no result
6 of 6 completed trials
Registrations
NCT00291070, NCT00372151, NCT01361204, NCT01851122, NCT02770105 and NCT03533556
Completion dates
oldest 2006-07; newest 2018-08-31
Show the evidence
Trial
NCT00291070
2006-07
NCT00372151
2008-12
NCT01361204
2012-04
NCT01851122
2012-10
NCT02770105
2016-06
NCT03533556
2018-08-31
Q8
At the median, L-theanine's trials enrolled 23 people — anything larger?
Median enrolment
23
Largest enrolment
100
Registered trials counted
10
Q9
What do 2 spontaneous reports say about L-theanine — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
L-theanine appears in spontaneous reports to regulators. Across the 1 most-reported reaction term, 2 reaction mentions were counted: metal poisoning 2. open-targets-adr · CHEMBL3039113 · 2026-06-24
Show the evidence
metal poisoning
2
recorded 2026-06-24 · last checked 2026-09-04
Q10
Was L-theanine studied with exercise?
exercise is named in L-theanine's label sentences: "To study the effect of theanine on delaying exercise-induced fatigue, and reveal its possible mechanism．Mice were randomized into 4 groups：three groups of theanine at doses of 5.6、8.4、12.6 mg/(kg bw·d), and one control group given distilled water．After 30 d，burdened swimming time，serum BUN，liver…" openfda-label+europepmc · 2005-01-01
1 recorded statement; exercise
Show the evidence
exercise
To study the effect of theanine on delaying exercise-induced fatigue, and reveal its possible mechanism．Mice were randomized into 4 groups：three groups of theanine at doses of 5.6、8.4、12.6 mg/(kg bw·d), and one control group given distilled water．After 30 d，burdened swimming time，serum BUN，liver glycogen，and monoamine neurotransmitters（5-HT、DA and NE） concentrations in brain were…
recorded 2005-01-01 · last checked 2026-09-04
Q11
What is recorded about L-theanine and autophagy?
"This study revealed that the modulation of the JNK/c-Jun/Beclin-1/Bcl-2 pathway by l-theanine ameliorates isoprenaline-induced HF via the regulation of autophagic and inflammatory pathways." — where L-theanine and autophagy appear together. Europe PMC · pathway abstract search · 2026-07-06
"This study revealed that the modulation of the JNK/c-Jun/Beclin-1/Bcl-2 pathway by l-theanine ameliorates isoprenaline-induced HF via the regulation of autophagic and inflammatory pathways."
sirtuin
PMID 42392245
"However, EGCG, l-theanine and theophylline effectively abolished all these high-glucose-induced effects on senescence and SIRT1/PGC-1α axis in PTECs, EMT in DTECs, and renal fibroblast activation."
PMID 40328913
"Notably, the SIRT1 inhibitor EX-527 can counteract the protective effect of L-theanine against ferroptosis in cardiomyocytes."
PMID 40328913
"These findings highlight that L-theanine mitigates SD-induced cardiac injury primarily by suppressing ferroptosis through SIRT1 in cardiomyocytes."
AMPKPMID 40714509
"Mechanistically, L-theanine modulates glutamate receptors to enhance neuroprotection (BDNF upregulation, cortisol reduction), activates AMPK for anti-obesity effects (lipid oxidation, adiponectin secretion), and activates of γδ T cells to bolster immunomodulation."
autophagy
PMID 40504752
"Recently, autophagy modulation has been proven to display a beneficial effect against several diseases. l-Theanine (LTA), found in green tea, possesses neuroprotective, anti-inflammatory, antioxidant, and antiaging properties."
PMID 38893565
"Mechanistic investigations showed that L-theanine treatment enhanced the removal of mtDNA damage and extended lifespan by activating autophagy, mitophagy, mitochondrial dynamics, and mitochondrial unfolded protein response (UPR<sup>mt</sup>) in UVC-exposed nematodes."
mTORPMID 35428314
"Mechanic studies showed that L-theanine significantly inhibited the nucleus translocation of sterol regulatory element binding protein 1c (SREBP-1c) through AMPK-mTOR signaling pathway, thereby contributing to the reduction of fatty acid synthesis."
AMPK
PMID 35428314
"Mechanic studies showed that L-theanine significantly inhibited the nucleus translocation of sterol regulatory element binding protein 1c (SREBP-1c) through AMPK-mTOR signaling pathway, thereby contributing to the reduction of fatty acid synthesis."
PMID 35428314
"We also identified that L-theanine enhanced fatty acid β-oxidation by increasing the expression of peroxisome proliferator-activated receptor α (PPARα) and carnitine palmitoyltransferase-1 A (CPT1A) through AMP-activated protein kinase (AMPK)."
mTOR
PMID 36034895
"EGCG + L-theanine inhibited inflammation and aggregate formation pathways, significantly increased the percentage of G0/G1 in the cell cycle, downregulated the expression of proteins such as p-mTOR, Cyclin D1, and Cyclin B1, upregulated the expression of GAP43, Klotho, p-AMPK, and other proteins, promoted mitochondrial activity and energy metabolism, and had repair and regeneration effects on…"
PMID 32057039
"Moreover, l-theanine upregulated the expression of PFKL, glycogen synthase 2 (GYS2), ribosomal protein S6 (S6), INSR, IRS, and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) proteins; downregulated the expression of FAS, sterol regulatory element binding protein-1c (SREBP-1c), and HMGCR proteins; enhanced the phosphorylation of the mammal target of rapamycin (mTOR), ribosomal protein S6…"
recorded 2026-07-06 · last checked 2026-09-04
Where it is registeredIdentifiers, relations and other names
ClinicalTrials.gov — US Government work · Europe PMC — metadata only, under the recorded legal gate · Open Targets 26.06 — CC0 · derived from this page's own recorded fields; no external licence · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
✗ required summary fields resolved: 5 required field(s) not terminal: Why people use it, Best-supported result, Most important common problem, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 9 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.