Best L-theanine supplement
James BevanUpdated Oct 21, 2026
L-theanine is the tea amino acid that turns up in most of the brain supplements we've audited, and it's also sold on its own as a cheap capsule. But do the stacks give you the amount the studies used, and is a single capsule the better buy? To find out, we've checked every L-theanine product we've audited against the studies, worked out what each costs a day, and picked the capsule we'd buy.
Quick verdict
Nootropics Depot L-Theanine
The one we'd buy. The trials' usual 200 mg, a lab report on every batch, 18 cents a day.
- Price per day
- $0.18
- Capsules a day
- 1
- Dose per capsule
- 200 mg
- Form
- Generic
- Evidence
- Moderate
- Capsules per bottle
- 90
- Against the studies
- Within range
Runner-up
Momentous L-TheanineAudit rating 9.0/10$0.67 a day4.6/5 from 303 Amazon buyers
How we rated these We audited 11 brain supplements and four single capsules from their labels and published lab reports, weighting dose fit at 40%, evidence 30%, transparency 20% and testing 10%. Every price is a US price. Audited Oct 21, 2026 How we audit We may earn a commission from links on this page, at no extra cost to you. How we make money
In this guide
What our audit found
We checked 11 brain supplements and four single capsules that contain L-theanine, and these five findings matter most if you're buying.
-
Every stack that prints its dose reaches the floor
The ten brain supplements that print their L-theanine give 100 to 200 mg, inside the 100 to 400 mg the studies used. Alpha Brain is the exception, because its amount sits inside a blend.
-
Only one single capsule uses Suntheanine
Thorne's capsule is the only pick that names Suntheanine, the branded form several of the trials used, and it costs about four times as much as our pick.3289
-
Lab reports differ a lot
Nootropics Depot's lot report measured 205.8 mg per capsule, from a lab the brand set up.2829 Momentous carries NSF Certified for Sport and lot reports too.3031 Thorne relies on an NSF/ANSI 173 listing with no lot report, and Nutricost publishes none.3334
-
Daily use didn't beat placebo on thinking tests overall
After 12 weeks at 100.6 mg a day, and after 4 weeks at 200 mg a day, the trials found no difference from placebo on cognitive tests overall. Only the half of Hidese 2019's group with lower starting scores improved on verbal fluency.89 The reliable result comes from a single dose.
-
Unilever paid for half of the caffeine-pairing trials
Three of the six trials behind the theanine and caffeine pairing that many brain supplements lean on were run by Unilever.222324
Best L-theanine supplements
Nootropics Depot's capsule is 200 mg, the dose most trials used, with a lab report that measured 205.8 mg, and it's the one we'd choose. Thorne's is the one to buy if you want Suntheanine, at about four times the price.
Generic L-theanine at the 200 mg most trials used, and its lot report also confirms the L-form. Every lot is tested by a lab the brand set up.
- 200 mg a day
- 1 capsule, $0.18 a day
- 400 mg a day
- 2 capsules, $0.36 a day
- Testing
- A lab report for every lot with the amount measured, from a lab the brand founded
- Refund
- Unopened bottles only, 30 days
- Capsule
- Vegetable cellulose
- Dose fit 40%Dose fit 100
- Evidence 30%Evidence 70
L-theanine's evidence grade is moderate.
- Transparency 20%Transparency 95
Dose and form printed in full. Five points come off because we read the label online, not on a bottle we bought.
- Testing 10%Testing 100
- nootropicsdepot.com direct
- Listed price
- $15.99
- Per serving
- $0.18
- Status
- In stock
- Amazon (official store)
- Price
- Check price on Amazon
- Status
- In stock, sold by Nootropics Depot
NSF Certified for Sport, with a public lab report for each lot, at 67 cents a capsule. Its Amazon listing was unavailable when we checked.
- 200 mg a day
- 1 capsule, $0.67 a day
- 400 mg a day
- 2 capsules, $1.33 a day
- Testing
- NSF Certified for Sport, plus a public lab report for each lot
- Refund
- The product page says 30 days money back, but the refund policy says it generally doesn't accept returns of delivered products
- Capsule
- Hypromellose (plant cellulose)
- Dose fit 40%Dose fit 100
- Evidence 30%Evidence 70
L-theanine's evidence grade is moderate.
- Transparency 20%Transparency 95
Dose and form printed in full. Five points come off because we read the label online, not on a bottle we bought.
- Testing 10%Testing 100
- livemomentous.com direct
- Listed price
- $39.99
- Per serving
- $0.67
- Status
- In stock
The only pick that uses Suntheanine, the branded form several trials used. It's listed under NSF/ANSI 173 but publishes no lot report, at 76 cents a capsule.
- 200 mg a day
- 1 capsule, $0.76 a day
- 400 mg a day
- 2 capsules, $1.51 a day
- Testing
- Listed under NSF/ANSI 173, with no lot lab report published
- Refund
- 60 days from purchase, with a 25% restocking fee on approved returns
- Capsule
- Hypromellose (plant cellulose)
- Dose fit 40%Dose fit 100
- Evidence 30%Evidence 70
L-theanine's evidence grade is moderate.
- Transparency 20%Transparency 95
Dose and form printed in full. Five points come off because we read the label online, not on a bottle we bought.
- Testing 10%Testing 100
- thorne.com direct
- Listed price
- $68.00
- Per serving
- $0.76
- Status
- In stock
The cheapest at 12 cents a capsule, in a gelatin capsule. It publishes no lab report.
- 200 mg a day
- 1 capsule, $0.12 a day
- 400 mg a day
- 2 capsules, $0.23 a day
- Testing
- None published
- Refund
- 60 days, money back minus shipping
- Capsule
- Gelatin
- Dose fit 40%Dose fit 100
- Evidence 30%Evidence 70
L-theanine's evidence grade is moderate.
- Transparency 20%Transparency 95
Dose and form printed in full. Five points come off because we read the label online, not on a bottle we bought.
- Testing 10%Testing 0
No lab report is published.
- nutricost.com direct
- Listed price
- $13.97
- Per serving
- $0.12
- Status
- In stock
- Amazon (official store)
- Price
- Check price on Amazon
- Status
- In stock; sold by eSupplements (Nutricost's Amazon seller)
L-theanine in brain supplements
This table ranks the audited brain supplements that contain L-theanine, with the amount each one gives and what each formula costs for the studied floor.
Brain supplements we've audited that contain L-theanine
$1.67 of the stack per 100 mg of L-theanine
$1.56 of the stack per 100 mg of L-theanine
$1.12 of the stack per 100 mg of L-theanine
L-theanine
$2.58 of the stack per 100 mg of L-theanine
$2.30 of the stack per 100 mg of L-theanine
$6.25 of the stack per 100 mg of L-theanine
$3.98 of the stack per 100 mg of L-theanine
$2.33 of the stack per 100 mg of L-theanine
$1.50 of the stack per 100 mg of L-theanine
$2.17 of the stack per 100 mg of L-theanine
No amount to price
Each price covers the whole brain supplement for a day, scaled to 100 mg of L-theanine as a fraction of a serving, not a dose to take, rather than L-theanine alone. If you're buying mainly for L-theanine, a single capsule gives you 200 mg for 12 to 76 cents.273234
Is L-theanine worth buying, and who it suits
L-theanine is worth considering before a task. We wouldn't buy it as a daily thinking supplement. A meta-analysis of 31 trials found faster choice reaction time after a single 200 mg dose.1 A second review found the effect was small to moderate and appeared within the hour.2 Daily use for weeks didn't beat placebo on thinking tests.89
Stress results were modest and came mostly from trials at high risk of bias. The anxiety results weren't consistent.1
Every product we checked that prints its amount gives at least 100 mg. A single 200 mg capsule costs 12 to 76 cents, so dose is rarely the problem.
L-theanine is an amino acid from tea, sold as plain L-theanine or Suntheanine, Taiyo's branded form. A cup of green tea has about 25 mg. Getting the 200 mg most trials used would take about eight cups.8
If you want a calmer, slightly quicker hour before a task, the single-dose findings offer some support, whether taken alone or with coffee.12 For sleep, the evidence rests mostly on what participants reported themselves. Few of those trials used theanine on its own.39
For daily memory or focus, it's harder to recommend. Daily use didn't beat placebo overall.89
No trial has tested it in pregnancy or breastfeeding, and Thorne's label tells anyone pregnant to check with a practitioner first.32 For safety in full, the FDA's GRAS notices for L-theanine, four of them each closed with no questions, are the most complete public assessments.26
How much to take, and when
The trials tell you how much L-theanine to look for on a label, and when they gave it.
- Study dose benchmark
- 100 mg a day
- Doses in studies with a benefit
- 100 mg to 400 mg a day
- Most-studied single dose
- 200 mg, 30 to 60 minutes before a task
- Time to any effect
- Within the hour for reaction time. Sleep sub-scores improved after 4 weeks of 200 mg a day.
Across the studies, daily amounts ranged from 100 to 400 mg. At 100 mg, one trial found faster simple reaction time, while another found no effect from theanine alone.615 The meta-analysis result came from 200 mg, and 400 mg did no better on behavior.16
Attention trials gave it 30 to 60 minutes before the task, while sleep trials gave it at bedtime.19 No trial compared morning with evening for the same outcome.
What the trials found
Our evidence grade for L-theanine rests on the human trials, the positive ones and the ones that found nothing.
ModerateA small, quick effect on reaction time from a single dose in a meta-analysis of 31 trials. Daily use for 4 to 12 weeks didn't beat placebo on thinking tests overall.
L-theanine is an amino acid found in tea. A 50 mg dose increased resting alpha-wave activity, which is a brain-wave marker rather than a result on a task.14 One small trial also found lower heart-rate and salivary stress responses to a lab stressor.11
Studies of theanine alone in healthy adults have found benefits, but others have found no difference.
| Study | Who took part | Dose and length | What happened |
|---|---|---|---|
| Lu 200410Randomized, double-blind, placebo-controlled, against alprazolam | 16 healthy adults | One 200 mg dose | No clear benefitNo calming effect under induced anxiety, and alprazolam had none either. Slightly more relaxed on one mood scale at rest. |
| Kimura 200711Double-blind crossover, four conditions | 12 healthy adults | One 200 mg dose, per later reviews (the abstract gives no dose) | Showed a benefitLower heart rate and salivary IgA response to a mental arithmetic stressor than placebo. Co-authored by the Suntheanine maker. |
| Haskell 200812Randomized, double-blind, placebo-controlled crossover | 27 healthy adults | One 250 mg dose, alone and with 150 mg caffeine | No clear benefitTheanine alone raised headache ratings and worsened serial subtraction. The combination improved several measures. |
| Rogers 200813Randomized, double-blind, placebo-controlled | 48 healthy adults | One 200 mg dose, alone and with 250 mg caffeine | No clear benefitTheanine alone slowed reaction time on a visual task and damped caffeine's blood-pressure rise. No change in alertness. |
| Nobre 200814Placebo-controlled, two studies | 35 healthy young adults in the first study (the second study's size isn't in the abstract) | One 50 mg dose | Showed a benefitMore resting alpha-wave brain activity than placebo over 45 to 105 minutes. A brain-wave marker, not a task result. Unilever-funded. |
| Kelly 200815Double-blind crossover, four conditions | Healthy adults (number not in the abstract) | One 100 mg dose, alone and with 50 mg caffeine | No clear benefitTheanine alone had no effect on the attention task. The combination improved it. |
| Yoto 201217Crossover, three conditions | 14 healthy adults | One 200 mg dose | Showed a benefitSmaller blood-pressure rise under mental stress in people who reacted strongly, and lower tension scores. |
| Unno 201318Single-blind group comparison | 20 pharmacy students on placement | 200 mg twice a day for 17 days | Showed a benefitLower morning salivary stress enzyme and self-rated stress. Only the participants were blinded. |
| Kahathuduwa 201719Placebo-controlled five-way crossover | 20 healthy men | One 200 mg dose, alone and with 160 mg caffeine | Showed a benefitFaster visual recognition reaction time with theanine alone, caffeine alone and the pair. |
| Kahathuduwa 201820Randomized four-way crossover with brain scans | 9 healthy men | One 200 mg dose, alone and with 160 mg caffeine | Showed a benefitFaster responses to targets with theanine alone and with the pair. |
| Hidese 20199Randomized, double-blind, placebo-controlled crossover | 30 healthy adults, average age 48 | 200 mg a day (Suntheanine) for 4 weeks | Showed a benefitAgainst placebo, three sleep sub-scores improved, and verbal fluency did in the half with lower starting scores. Stress and anxiety scores fell only against baseline, and no cognitive test beat placebo overall. Funded by the Suntheanine maker. |
| Baba 20218Randomized, double-blind, placebo-controlled | 69 adults aged 50 to 69 (50 analysed) | 100.6 mg a day (Suntheanine) for 12 weeks | No clear benefitA single dose improved attention and working-memory scores. After 12 weeks of daily use, no difference from placebo. Sponsored by a tea company. |
| Dassanayake 20227Double-blind, placebo-controlled four-way crossover | 27 healthy young adults | One dose of 100, 200 or 400 mg | No clear benefitOnly 400 mg sped up a brain-wave measure of attention. No dose changed reaction time. |
| Dassanayake 20236Double-blind, placebo-controlled four-way crossover | 32 healthy young adults | One dose of 100, 200 or 400 mg | Showed a benefitSimple reaction time about 16 ms faster at 100 and 200 mg. No change in sustained attention or impulse control. |
| Karunaratne 202521Double-blind, placebo-controlled crossover | 24 sleep-deprived adults aged 20 to 25 | One 200 mg dose | No clear benefitFewer false alarms on a traffic-scene task after theanine, a change placebo didn't show. Reaction-time changes didn't differ from placebo. |
- Lu 200410No clear benefit
Randomized, double-blind, placebo-controlled, against alprazolam
16 healthy adults
One 200 mg dose
No calming effect under induced anxiety, and alprazolam had none either. Slightly more relaxed on one mood scale at rest.
- Kimura 200711Showed a benefit
Double-blind crossover, four conditions
12 healthy adults
One 200 mg dose, per later reviews (the abstract gives no dose)
Lower heart rate and salivary IgA response to a mental arithmetic stressor than placebo. Co-authored by the Suntheanine maker.
- Haskell 200812No clear benefit
Randomized, double-blind, placebo-controlled crossover
27 healthy adults
One 250 mg dose, alone and with 150 mg caffeine
Theanine alone raised headache ratings and worsened serial subtraction. The combination improved several measures.
- Rogers 200813No clear benefit
Randomized, double-blind, placebo-controlled
48 healthy adults
One 200 mg dose, alone and with 250 mg caffeine
Theanine alone slowed reaction time on a visual task and damped caffeine's blood-pressure rise. No change in alertness.
- Nobre 200814Showed a benefit
Placebo-controlled, two studies
35 healthy young adults in the first study (the second study's size isn't in the abstract)
One 50 mg dose
More resting alpha-wave brain activity than placebo over 45 to 105 minutes. A brain-wave marker, not a task result. Unilever-funded.
- Kelly 200815No clear benefit
Double-blind crossover, four conditions
Healthy adults (number not in the abstract)
One 100 mg dose, alone and with 50 mg caffeine
Theanine alone had no effect on the attention task. The combination improved it.
- Yoto 201217Showed a benefit
Crossover, three conditions
14 healthy adults
One 200 mg dose
Smaller blood-pressure rise under mental stress in people who reacted strongly, and lower tension scores.
- Unno 201318Showed a benefit
Single-blind group comparison
20 pharmacy students on placement
200 mg twice a day for 17 days
Lower morning salivary stress enzyme and self-rated stress. Only the participants were blinded.
- Kahathuduwa 201719Showed a benefit
Placebo-controlled five-way crossover
20 healthy men
One 200 mg dose, alone and with 160 mg caffeine
Faster visual recognition reaction time with theanine alone, caffeine alone and the pair.
- Kahathuduwa 201820Showed a benefit
Randomized four-way crossover with brain scans
9 healthy men
One 200 mg dose, alone and with 160 mg caffeine
Faster responses to targets with theanine alone and with the pair.
- Hidese 20199Showed a benefit
Randomized, double-blind, placebo-controlled crossover
30 healthy adults, average age 48
200 mg a day (Suntheanine) for 4 weeks
Against placebo, three sleep sub-scores improved, and verbal fluency did in the half with lower starting scores. Stress and anxiety scores fell only against baseline, and no cognitive test beat placebo overall. Funded by the Suntheanine maker.
- Baba 20218No clear benefit
Randomized, double-blind, placebo-controlled
69 adults aged 50 to 69 (50 analysed)
100.6 mg a day (Suntheanine) for 12 weeks
A single dose improved attention and working-memory scores. After 12 weeks of daily use, no difference from placebo. Sponsored by a tea company.
- Dassanayake 20227No clear benefit
Double-blind, placebo-controlled four-way crossover
27 healthy young adults
One dose of 100, 200 or 400 mg
Only 400 mg sped up a brain-wave measure of attention. No dose changed reaction time.
- Dassanayake 20236Showed a benefit
Double-blind, placebo-controlled four-way crossover
32 healthy young adults
One dose of 100, 200 or 400 mg
Simple reaction time about 16 ms faster at 100 and 200 mg. No change in sustained attention or impulse control.
- Karunaratne 202521No clear benefit
Double-blind, placebo-controlled crossover
24 sleep-deprived adults aged 20 to 25
One 200 mg dose
Fewer false alarms on a traffic-scene task after theanine, a change placebo didn't show. Reaction-time changes didn't differ from placebo.
In the dose trials, 100 and 200 mg sped up simple reaction time by about 16 ms. The 400 mg dose didn't improve that task, though only 400 mg changed a brain-wave measure of attention.67
Daily use gave different results from a single dose. Baba 2021 found a single dose helped attention, but after 12 weeks of daily use there was no difference from placebo.8
Hidese 2019 found three sleep sub-scores improved against placebo. Stress and anxiety fell only compared with participants' starting scores, and no thinking test beat placebo overall. Verbal fluency did beat placebo in the half who started with lower scores.9
Some results went the wrong way. At 200 mg it had no calming effect under induced anxiety, 250 mg on its own raised headache ratings and worsened serial subtraction, and 200 mg on its own slowed reaction time on a visual task.101213
Many brain supplements pair theanine with caffeine, and that pairing has trials of its own. Those results apply to the pair, rather than to theanine alone.
| Study | Who took part | Dose and length | What happened |
|---|---|---|---|
| Owen 200822Placebo-controlled crossover | 27 healthy adults | 100 mg theanine with 50 mg caffeine | Showed a benefitFaster, more accurate task switching at 60 minutes. Unilever-funded. |
| Giesbrecht 201023Placebo-controlled crossover | 44 healthy adults | 97 mg theanine with 40 mg caffeine | Showed a benefitBetter task-switching accuracy and alertness. No effect on visual search, choice reaction time or mental rotation. Unilever-funded. |
| Einöther 201024Placebo-controlled | Healthy adults (number not in the abstract) | 97 mg theanine with 40 mg caffeine | Showed a benefitBetter task switching. No change in alertness or attention across senses. Unilever-funded. |
| Haskell 200812Randomized, double-blind, placebo-controlled crossover | 27 healthy adults | 250 mg theanine with 150 mg caffeine | Showed a benefitThe pair improved accuracy, reaction time and working memory. Theanine alone made some measures worse. |
| Foxe 201216Double-blind randomized crossover | 27 healthy adults | 100 mg theanine with 50 mg caffeine, 2-hour task | Showed a benefitThe pair reduced the rise in errors over a long vigilance task, per the authors' summary. |
| Dodd 201525Double-blind, placebo-controlled | 24 healthy adults | 50 mg theanine with 75 mg caffeine | No clear benefitAdding theanine canceled caffeine's effects on thinking and mood at these doses. |
- Owen 200822Showed a benefit
Placebo-controlled crossover
27 healthy adults
100 mg theanine with 50 mg caffeine
Faster, more accurate task switching at 60 minutes. Unilever-funded.
- Giesbrecht 201023Showed a benefit
Placebo-controlled crossover
44 healthy adults
97 mg theanine with 40 mg caffeine
Better task-switching accuracy and alertness. No effect on visual search, choice reaction time or mental rotation. Unilever-funded.
- Einöther 201024Showed a benefit
Placebo-controlled
Healthy adults (number not in the abstract)
97 mg theanine with 40 mg caffeine
Better task switching. No change in alertness or attention across senses. Unilever-funded.
- Haskell 200812Showed a benefit
Randomized, double-blind, placebo-controlled crossover
27 healthy adults
250 mg theanine with 150 mg caffeine
The pair improved accuracy, reaction time and working memory. Theanine alone made some measures worse.
- Foxe 201216Showed a benefit
Double-blind randomized crossover
27 healthy adults
100 mg theanine with 50 mg caffeine, 2-hour task
The pair reduced the rise in errors over a long vigilance task, per the authors' summary.
- Dodd 201525No clear benefit
Double-blind, placebo-controlled
24 healthy adults
50 mg theanine with 75 mg caffeine
Adding theanine canceled caffeine's effects on thinking and mood at these doses.
Three Unilever trials found better task switching with about 100 mg of theanine and 40 to 50 mg of caffeine.222324 At 50 mg with 75 mg of caffeine, adding theanine canceled caffeine's effects on thinking and mood.25
The reviews that pooled trial results agree the effect is small, and the trials measured it only in the two hours after a dose.
| Study | Who took part | Dose and length | What happened |
|---|---|---|---|
| Gerolymos 20261Systematic review and meta-analysis of 31 randomized trials | 1,168 participants | Mostly a single 200 mg dose, 30 to 60 minutes before testing | Showed a benefitFaster choice reaction time and a modest stress effect driven by high-bias trials. No effect on fatigue, and no consistent effect on anxiety. |
| Payne 20252Systematic review of 50 trials, 15 pooled | Healthy participants | Theanine alone, or with caffeine | Showed a benefitA small-to-moderate effect on choice reaction time within the first hour. Small effects of the pair on vigilance and switching, with wide uncertainty. |
| Bulman 20253Systematic review and meta-analysis, 19 articles | 897 participants | Theanine alone or in combinations | Showed a benefitSmall improvements in self-rated sleep quality, time to fall asleep and daytime function. Few trials used theanine on its own. |
- Gerolymos 20261Showed a benefit
Systematic review and meta-analysis of 31 randomized trials
1,168 participants
Mostly a single 200 mg dose, 30 to 60 minutes before testing
Faster choice reaction time and a modest stress effect driven by high-bias trials. No effect on fatigue, and no consistent effect on anxiety.
- Payne 20252Showed a benefit
Systematic review of 50 trials, 15 pooled
Healthy participants
Theanine alone, or with caffeine
A small-to-moderate effect on choice reaction time within the first hour. Small effects of the pair on vigilance and switching, with wide uncertainty.
- Bulman 20253Showed a benefit
Systematic review and meta-analysis, 19 articles
897 participants
Theanine alone or in combinations
Small improvements in self-rated sleep quality, time to fall asleep and daytime function. Few trials used theanine on its own.
Reviews of the sleep trials and the stress and anxiety trials found possible benefits at 200 to 400 mg a day. The findings came mostly from participants' own ratings.45
Kimura 2007 and Hidese 2019 were funded or co-authored by the Suntheanine maker.119 A tea company sponsored Baba 2021.8 Unilever ran Owen 2008, Giesbrecht 2010 and Einöther 2010.222324
Independent research comes from the Peradeniya and Texas Tech trials and the Kelly and Foxe trials.671920211516 The senior author of the 2026 meta-analysis founded a supplement company.1
What it's stacked with
These are the ingredients L-theanine most often sits next to in brain supplements, and what the evidence says about each pairing.
Caffeine is the one pairing with its own trial record, and in one of those trials, at 50 mg with 75 mg of caffeine, theanine canceled caffeine's effects.22232425 Citicoline and tyrosine turn up next to it in the caffeine-free and stimulant formulas, with no trial of either pair that we could find.
Questions people ask
How long does L-theanine take to work?
Can you take L-theanine every day?
How much L-theanine should you take with caffeine?
Is L-theanine the same as green tea?
Is Suntheanine better than generic L-theanine?
Sources
34 sources cited
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- Bulman A, et al. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev, 2025. Abstract read. Accessed Oct 19, 2026. PMID 40056718
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- Unno K, et al. Anti-stress effect of theanine on students during pharmacy practice. Pharmacol Biochem Behav, 2013. Abstract read. Accessed Oct 19, 2026. PMID 24051231
- Kahathuduwa CN, et al. Acute effects of theanine, caffeine and theanine-caffeine combination on attention. Nutr Neurosci, 2017. Abstract read. Accessed Oct 19, 2026. PMID 26869148
- Kahathuduwa CN, et al. L-theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging study. Nutr Res, 2018. Abstract read. Accessed Oct 19, 2026. PMID 29420994
- Karunaratne UW, et al. Effect of L-theanine on selective attention in a traffic-related reaction task in sleep-deprived young adults. Nutr Neurosci, 2025. Abstract read. Accessed Oct 19, 2026. PMID 39052627
- Owen GN, et al. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci, 2008. Abstract read. Accessed Oct 19, 2026. PMID 18681988
- Giesbrecht T, et al. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci, 2010. Abstract read. Accessed Oct 19, 2026. PMID 21040626
- Einöther SJ, et al. L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness. Appetite, 2010. Abstract read. Accessed Oct 19, 2026. PMID 20079786
- Dodd FL, et al. A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology, 2015. Abstract read. Accessed Oct 19, 2026. PMID 25761837
- US Food and Drug Administration. GRAS Notice Inventory, search for theanine: GRN 209 (2007), GRN 338 (2010), GRN 501 (2014) and GRN 1311 (2026), each closed with "FDA has no questions"; GRN 1344 pending. Accessed Oct 19, 2026. FDA GRAS notices
- Nootropics Depot. L-Theanine Capsules 200 mg: product page, Supplement Facts label, price and returns policy. Accessed Oct 19, 2026. nootropicsdepot.com
- Omnient Labs for Nootropics Depot. Certificate of analysis, L-Theanine Capsules 200 mg, lot LTHCS1082426, Aug 24, 2026: 205.8 mg L-theanine per capsule by UPLC. Accessed Oct 19, 2026. Lot lab report (PDF)
- Nootropics Depot. Meet our third party labs: Omnient Labs "was started as an ISO accredited lab to do advanced lab testing for Nootropics Depot." Accessed Oct 19, 2026. nootropicsdepot.com
- Momentous. L-Theanine 200 mg: product page, Supplement Facts label, price and lot lab reports. Accessed Oct 19, 2026. livemomentous.com
- NSF Certified for Sport. Momentous L-Theanine, 60 capsules, listing. Accessed Oct 19, 2026. NSF Certified for Sport
- Thorne. Theanine 200 mg (Suntheanine): product page, Supplement Facts label and price. Accessed Oct 19, 2026. thorne.com
- NSF/ANSI 173 dietary supplement listings, Thorne: Theanine, capsule. Accessed Oct 19, 2026. NSF listing
- Nutricost. L-Theanine 200 mg capsules: product page, Supplement Facts label, price and 60-day guarantee. Accessed Oct 19, 2026. nutricost.com
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