Ashwagandha vs L-Theanine: Which Is Better for Stress?
Should I take ashwagandha or L-theanine for stress?
Both score anxiety 7.5, so the tie-breaker is time. L-theanine works in about an hour and you take it when you need it. Ashwagandha takes eight weeks and lowers cortisol itself. L-theanine scores 7.9 overall against 6.8, costs a quarter as much, and excludes almost nobody.
- Anxiety is an exact 7.5 tie and sleep quality an exact 6.5 tie. The overall gap, 7.9 against 6.8, comes from cost and safety rather than from calm.
- L-theanine acts in about an hour. Ashwagandha needs a week for a first signal and eight for full effect, and it lowers measured cortisol where L-theanine does not.
- L-theanine wins everything cognitive: focus 7.5 to 5.0, flow state 6.5 to 2.5, reaction time 6.0 to 3.5. It is the only one of the two that pairs with caffeine.
- Cost is not close. L-theanine runs $3 to $8 a month at 200 mg. Ashwagandha runs $15 to $30 for third-party-tested KSM-66.
- Safety is not close either. L-theanine's downside total is 0.261 against ashwagandha's 1.258, driven by documented liver-injury cases and thyroid stimulation.
- Ashwagandha's exclusion list runs to eleven items including liver disease, thyroid disease and levothyroxine. It also has a built-in stop: 8 to 12 weeks continuous, then a break.
- The best L-theanine evidence is not for anxiety alone. Four separate trials tested it with caffeine, and Sarris 2019 found it did not clearly beat placebo as an add-on in generalized anxiety disorder.
At a Glance
Ashwagandha
- Efficacy 3.8
- Breadth 4.5
- Evidence 4.0
- Speed 3.0
- Durability 2.5
- Bioindividuality 3.5
- Safety Risk 2.5
- Side Effects 2.3
- Cost 1.5
- Effort 1.0
- Opportunity Cost 2.0
- Dependency 1.5
- Reversibility 1.5
- Stress Resilience
- Anxiety
- Sleep Quality
- Hormonal
Withanolide-standardized root extract. BioHarmony 6.8, worth trying.
L-Theanine
- Efficacy 3.4
- Breadth 3.6
- Evidence 4.3
- Speed 4.0
- Durability 2.0
- Bioindividuality 3.4
- Safety Risk 1.2
- Side Effects 1.3
- Cost 1.2
- Effort 1.1
- Opportunity Cost 1.3
- Dependency 1.4
- Reversibility 1.0
- Anxiety
- Cognition Focus
- Stress Resilience
- Sleep Quality
Amino acid from tea leaf. BioHarmony 7.9, strong recommend.
Head-to-Head Verdict
| Use Case | Winner | Rationale |
|---|---|---|
| Anxiety | Tie | Both 7.5, an exact tie, and they earn it differently. Ashwagandha's case is pooled and repeated: Fatima 2024 across 5 RCTs and 254 people on HAM-A scores, Arumugam 2024 across 9 RCTs and 558 people including serum cortisol. L-theanine's is faster but softer, and Sarris 2019 found it did not clearly improve anxiety severity in generalized anxiety disorder. |
| Stress Resilience | Ashwagandha | Ashwagandha 7.5 against L-theanine's 7.0, and the reason is that ashwagandha moves the hormone rather than the feeling. Arumugam 2024 found serum cortisol fell alongside perceived stress, and Bachour 2025 pooled 15 studies and 873 people reporting reduced HAM-A, PSS and cortisol at eight weeks. L-theanine damps stress reactivity in the moment without changing the axis that produces it. |
| Cognition Focus | L-Theanine | L-theanine 7.5 against ashwagandha's 5.0, the widest gap on the page. The caveat is that most of the evidence is for the combination rather than the amino acid alone: Owen 2008, Kelly 2008, Giesbrecht 2010 and Haskell 2008 all tested L-theanine with caffeine and found improved attention switching and better task-switching accuracy. |
| Flow State | L-Theanine | L-theanine 6.5 against ashwagandha's 2.5. The mechanism here is unusually concrete for a supplement: Nobre 2008 measured increased alpha-band EEG activity in relaxed-attention contexts, at 50 mg rather than the 200 mg commonly quoted. Alpha activity is the electrical signature of calm alertness, which is what people mean by flow. Ashwagandha has no equivalent. |
| Reaction Time | L-Theanine | L-theanine 6.0 against ashwagandha's 3.5, with an important limit. Matyus 2025 pooled 5 RCTs in 148 healthy adults and found a dose-dependent benefit on rapid visual information processing reaction time, but no significant effect on simple reaction time or Stroop outcomes. So the benefit is on sustained attention tasks, not on raw speed. |
| Mood | Ashwagandha | Ashwagandha 6.0 against L-theanine's 5.5, on the deeper dataset. Alsanie 2026 is a dose-response meta-analysis across 22 RCTs and 1391 people showing improvement in stress, anxiety and depression, with the authors' own low-certainty caveat. L-theanine's mood data comes largely from psychiatric populations: Ritsner 2011 in schizophrenia and Moshfeghinia 2024 across mental disorders generally. |
| HRV Vagal Tone | L-Theanine | L-theanine 5.5 against ashwagandha's 4.0. This follows the same acute mechanism as flow state: stress-reactivity dampening and alpha-band activity, both of which show up within an hour. Hidese 2019 was a small crossover RCT improving stress-related symptoms and self-reported anxiety in healthy adults. Neither report holds a dedicated heart-rate-variability trial. |
| Sleep Quality | Tie | Both 6.5, an exact tie, and both have real meta-analytic support. Bulman 2025 pooled 19 articles and 897 participants on L-theanine, finding improved subjective sleep onset latency, daytime dysfunction and overall quality while objective measures were less convincing. Cheah 2021 found a small significant sleep effect for ashwagandha, stronger in insomnia. |
| Sleep Architecture | Tie | L-theanine 5.0 against ashwagandha's 4.5, inside the noise. Langade 2019 measured objective as well as subjective sleep outcomes on ashwagandha, and Lyon 2011 improved some objective sleep-quality measures in boys with ADHD on L-theanine. Cotter 2026 noted L-theanine at 200 to 450 mg/day supported latency, maintenance and efficiency more than total sleep time. |
| Creativity | L-Theanine | L-theanine 4.0 against ashwagandha's 2.0, and both numbers are modest enough to keep in perspective. The alpha-band finding in Nobre 2008 is the whole basis: relaxed attention is the state associated with divergent thinking. No trial on either compound has measured a creativity endpoint directly. |
| Pediatric | L-Theanine | L-theanine 4.0 against ashwagandha's 1.5, and this is the clearest population split on the page. Lyon 2011 ran a randomized double-blind placebo-controlled trial in boys with ADHD and improved some objective sleep-quality measures with good tolerability. Its own contraindication list still says children without pediatric clinician guidance. Ashwagandha has no pediatric data at all. |
| Immune Function | Ashwagandha | Ashwagandha 5.0 against L-theanine's 2.0, and it is a breadth row rather than a calm row. Ferreira 2025 overviews 11 systematic reviews covering 9005 people with signals across endurance, strength, anxiety, sleep and sexual function. That breadth is why ashwagandha scores above 5.0 on thirteen rows where L-theanine scores at the floor. |
Cost Comparison
| Intervention | Monthly Cost | Notes |
|---|---|---|
| Ashwagandha | $15 to $30 | ESTIMATE, priced 2026-09-07, ordinary supplement retail. KSM-66 at 600 mg/day runs $15 to $30 a month for third-party-tested extract, and the standardized extracts are what every trial cited here actually used. Generic root powder is $5 to $15 and carries adulteration risk, which Saper 2008 documented in internet-sold Ayurvedic products generally. |
| L-theanine | $3 to $8 | ESTIMATE, priced 2026-09-08, ordinary supplement retail. A standard 200 mg dose costs $0.10 to $0.25, so thirty daily doses is $3.00 to $7.50, and the 100 mg caffeine half of the alert-calm stack adds under a dollar a month. Branded Suntheanine costs slightly more for form clarity. FDA GRAS Notice 209 covers specified food uses up to 250 mg per serving. |
| The difference | About $12 to $22 a month, and L-theanine only costs on days you use it | L-theanine is roughly a quarter the price and it is also the only one you can take intermittently without losing the effect. It acts in about an hour, so a stressful Tuesday costs you 25 cents.Ashwagandha only works taken daily across an eight-week window, so the monthly figure is the real figure. Its own contraindication list caps continuous use at 8 to 12 weeks before a break, which cuts the annual spend but also means you cannot simply keep taking it. Over a year the honest comparison is roughly $40 to $90 against $36 to $90. |
When to Switch
Their clocks are the entire comparison, so get them right first. L-theanine gives a first noticeable effect in about an hour, on a four-week assessment window that is really about whether it suits you rather than whether it has built up.
Ashwagandha takes about a week for a first signal and eight for full effect, and eight weeks is also its window. If you took ashwagandha for three days and felt nothing, that is the expected result.
Switch from ashwagandha to L-theanine when the stress is episodic rather than chronic. The tell is that you know which hours are hard: a presentation, a commute, a caffeine crash at 2pm.
L-theanine is the only one of the two you can take situationally at 25 cents a dose, and it scores 7.5 on focus against ashwagandha's 5.0 for exactly that reason. Also switch if you have a thyroid condition, take levothyroxine, have any liver history, or hit the 8-to-12-week continuous-use ceiling.
Switch the other way, from L-theanine to ashwagandha, when the problem is a baseline rather than a moment. Measured cortisol is the difference: Arumugam 2024 pooled 9 RCTs where serum cortisol itself fell. If you feel keyed up all the time and no single hour is the problem, dampening reactivity for two hours will not fix it.
Running both is reasonable and neither contraindication list names the other, though both act on GABA-A, so add L-theanine to an established ashwagandha protocol rather than starting them together, and be careful if you are also on a sedative.
Who Should Pick What?
Someone who gets anxious before specific events but is otherwise fine
L-Theanine
Effect in about an hour at roughly 25 cents a dose, and no need to take it on days you do not need it. Ashwagandha cannot do this: its first signal is a week out and its full effect eight weeks. Take 200 mg an hour before, and know that Sarris 2019 found it did not clearly beat placebo in clinical generalized anxiety disorder.
Chronically stressed person who feels keyed up all the time
Ashwagandha
Stress resilience 7.5 against 7.0, and the reason is mechanism rather than the 0.5 gap. Arumugam 2024 pooled 9 RCTs and 558 people where serum cortisol fell alongside perceived stress. Take 300 mg of KSM-66 twice daily, judge at eight weeks, and plan the break before you start.
Knowledge worker who wants focus without the caffeine jitter
L-Theanine
Focus 7.5 against 5.0, flow state 6.5 against 2.5. Four separate trials (Owen 2008, Kelly 2008, Giesbrecht 2010, Haskell 2008) tested 200 mg L-theanine with 100 mg caffeine and found improved attention switching and reduced distraction. Note that most of the cognitive evidence is for the combination, not the amino acid alone.
Anyone with a thyroid condition or taking levothyroxine
L-Theanine
Ashwagandha is out. Hyperthyroidism, Graves' disease and thyroid hormone therapy are all on its contraindication list, Sharma 2018 showed it normalizes TSH, T3 and T4 in subclinical hypothyroidism, and a 2024 case report documents painless thyroiditis after use. That is the mechanism working in the wrong person.
Anyone with liver disease, current or past
L-Theanine
Ashwagandha is out again and this one is documented rather than theoretical. LiverTox 2024 lists it as a likely cause of clinically apparent liver injury and Bjornsson 2020 describes five cases with a mixed or cholestatic pattern and prolonged jaundice. L-theanine's downside total is 0.261 against ashwagandha's 1.258.
Parent looking for something for a child's sleep or focus
L-Theanine
Pediatric 4.0 against ashwagandha's 1.5, on the only pediatric trial either side holds: Lyon 2011, a randomized double-blind placebo-controlled study in boys with ADHD that improved some objective sleep-quality measures with good tolerability. Its own list still says children without pediatric clinician guidance, so this is a conversation with a pediatrician.
Someone on a sedative, a sleep drug or multiple blood pressure medications
Ashwagandha
L-theanine's short exclusion list is aimed squarely at you: severe hypotension, multiple antihypertensives without clinician guidance, sedatives or hypnotics for additive sedation, and psychiatric medication without prescriber oversight. Ashwagandha also lists sedatives and benzodiazepines, so clear either with your prescriber first rather than switching on your own.
Lifter who wants the stress benefit without losing training adaptation
Ashwagandha
Muscle growth 5.0 against 1.0 and strength and power 5.0 against 1.5. Wankhede 2015 is a resistance-training RCT supporting strength, recovery and training adaptation, and Bonilla 2021 is a Bayesian meta-analysis of physical performance. L-theanine has no performance mechanism. This is a breadth argument rather than a calm one.
Research Highlights
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Mechanism Difference
These two produce calm at different depths of the system. Ashwagandha is a withanolide-rich root extract that damps HPA-axis output and lowers cortisol while modulating GABA-A signaling, with secondary thyroid and androgen effects. It changes the hormone that produces the feeling, which takes weeks and reaches organs beyond the brain.L-theanine crosses the blood-brain barrier, modulates glutamate signaling at NMDA, AMPA and kainate receptors, supports GABA, serotonin and dopamine tone, and raises alpha-band EEG activity in relaxed-attention states. It changes the feeling without touching the hormone, which is why it works in an hour and why it scores 7.5 on focus against ashwagandha's 5.0.
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Safety Comparison
L-theanine is the safer of the two by a wide margin. Its downside total is 0.261 against ashwagandha's 1.258, and its exclusions are mostly additive effects: severe hypotension, multiple antihypertensives, sedatives or hypnotics, heavy alcohol, psychiatric medication without prescriber oversight. FDA GRAS Notice 209 covers food uses up to 250 mg per serving.Ashwagandha carries documented harms. LiverTox 2024 lists it as a likely cause of clinically apparent liver injury and Bjornsson 2020 describes five cases with prolonged jaundice. Sharma 2018 shows it moves TSH, T3 and T4, which is why thyroid disease and levothyroxine are contraindicated. Its own list caps continuous use at 8 to 12 weeks.
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Cost Comparison
L-theanine costs $3 to $8 a month at 200 mg daily, from a per-dose price of $0.10 to $0.25, with the caffeine half of the alert-calm stack adding under a dollar. Ashwagandha costs $15 to $30 a month for third-party-tested KSM-66 at 600 mg/day. Both are retail estimates priced September 2026.The larger difference is that only one of them has to be daily. L-theanine acts in about an hour, so a stressful Tuesday costs 25 cents and you skip the other days. Ashwagandha only works taken continuously across an eight-week window, so its monthly figure is the real one.
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Editorial Verdict
Anxiety is an exact 7.5 tie and sleep quality an exact 6.5 tie, so the overall gap of 7.9 against 6.8 is not about which one calms you. It is cost and safety: L-theanine costs a quarter as much and its downside total is 0.261 against 1.258.Take L-theanine when the stress is episodic and when focus matters, where it wins 7.5 to 5.0 on cognition and 6.5 to 2.5 on flow state. Take ashwagandha when the stress is a baseline, because it is the only one of the two that lowers measured cortisol (Arumugam 2024, 9 RCTs), and when the breadth beyond calm is worth the eleven-item exclusion list.
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Durability
Ashwagandha holds the higher durability score, 2.5 against L-theanine's 2.0, and neither survives stopping by much. L-theanine is explicitly acute: it acts in about an hour and is gone the same day, which is a feature when you want to dose situationally and a limitation when the problem is constant.Ashwagandha's benefit builds across its eight-week window and then runs into its own ceiling, because continuous use beyond 8 to 12 weeks without a break is on the contraindication list. So neither is a permanent fix. L-theanine is a tool you reach for and ashwagandha is a course you run.
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Combination Use
Running both is defensible and neither contraindication list names the other. The mechanisms overlap at GABA-A and diverge everywhere else: ashwagandha works through HPA-axis suppression and cortisol, L-theanine through glutamate modulation and alpha-band cortical activity.Two practical cautions. Both list sedatives as an interaction, so additive sedation is the thing to watch if you take anything for sleep. And start them separately: add L-theanine to an established ashwagandha protocol rather than beginning both at once, because ashwagandha needs eight weeks to be judged and L-theanine needs one hour.
Frequently Asked Questions
- Is L-theanine better than ashwagandha for anxiety?
- For anxiety specifically they tie at 7.5, so pick on timing. L-theanine works in about an hour and suits episodic anxiety. Ashwagandha needs eight weeks and lowers measured cortisol, which suits a constant baseline. Note the honest caveat on L-theanine: Sarris 2019 found it did not clearly beat placebo as an add-on in generalized anxiety disorder.
- Which one works faster?
- L-theanine, by orders of magnitude. First noticeable effect at about one hour with a four-week assessment window against ashwagandha's one week to first signal and eight weeks to full effect. That gap is the practical difference between them: one is a tool you reach for, the other is a course you run.
- Can I take ashwagandha and L-theanine together?
- Yes, and neither contraindication list names the other. They overlap at GABA-A and diverge everywhere else, so the combination is complementary rather than redundant. Add L-theanine to an established ashwagandha protocol rather than starting both together, and watch for additive sedation if you also take anything for sleep.
- Why does L-theanine score higher overall?
- Cost and safety, not calm. L-theanine is 7.9 against 6.8, and its downside total is 0.261 against ashwagandha's 1.258. It costs $3 to $8 a month against $15 to $30, excludes almost nobody, and has FDA GRAS status for food use. On the calm rows themselves they tie: anxiety 7.5 each, sleep quality 6.5 each.
- Do I need to take L-theanine with caffeine?
- For the cognitive benefit, mostly yes. Four separate trials that produced the focus evidence used 200 mg L-theanine with 100 mg caffeine (Owen 2008, Kelly 2008, Giesbrecht 2010, Haskell 2008), and Camfield 2014 pooled them. Taken alone it still supports calm and sleep, but the attention-switching results specifically came from the combination.
- Does ashwagandha need to be cycled?
- Yes. Continuous use beyond 8 to 12 weeks without a break is on its contraindication list, so plan the break before you start. That is also why its annual cost is lower than the monthly figure suggests. L-theanine has no such ceiling and can be taken daily or only on the days you need it.
- Which is safer?
- L-theanine, clearly. Its downside total is 0.261 against 1.258, and its exclusions are additive effects: severe hypotension, multiple antihypertensives, sedatives, heavy alcohol, psychiatric medication without oversight. Ashwagandha excludes thyroid disease, levothyroxine, liver disease, immunosuppressants, pregnancy and conception attempts, on the back of documented liver-injury cases.
- Will either help me focus?
- L-theanine will, modestly and with a limit worth knowing. Focus 7.5 against 5.0 and flow state 6.5 against 2.5, on alpha-band EEG activity (Nobre 2008) and the caffeine combination trials. Matyus 2025 found the benefit was on sustained-attention reaction time, with no significant effect on simple reaction time or Stroop performance.
Evidence Sources
- Meta-analysis Safety and efficacy of Withania somnifera for anxiety and insomnia: systematic review and meta-analysis (2024) 5 RCTs, n=254. Reduced HAM-A anxiety scores and improved several sleep parameters, with high heterogeneity.
- Meta-analysis Effects of Ashwagandha on stress and anxiety: systematic review and meta-analysis (2024) 9 RCTs, n=558. Reduced perceived stress, anxiety and serum cortisol versus placebo. The cortisol finding is what separates ashwagandha from L-theanine.
- Meta-analysis Effects of Ashwagandha supplements on cortisol, stress and anxiety levels in adults (2025) Conference abstract. 15 studies, n=873. Reduced HAM-A, PSS and cortisol at 8 weeks, with no significant quality-of-life improvement.
- Meta-analysis Effects of Ashwagandha on mental health in adults: systematic review and dose-response meta-analysis (2026) 22 RCTs, n=1391. Improvements in stress, anxiety and depression with dose and duration effects, at low certainty.
- Meta-analysis Effect of Ashwagandha extract on sleep: systematic review and meta-analysis (2021) Small significant overall sleep effect, stronger in insomnia, at higher doses and over longer durations.
- RCT Ashwagandha root extract in insomnia and anxiety: randomized placebo-controlled study (2019) Sleep and anxiety RCT with both objective and subjective sleep outcomes.
- RCT Withania somnifera supplementation on muscle strength and recovery: randomized controlled trial (2015) Resistance-training RCT supporting strength, recovery and training adaptation. L-theanine has no equivalent.
- RCT Ashwagandha root extract in subclinical hypothyroid patients (2018) Double-blind RCT supporting TSH, T3 and T4 normalization. The reason thyroid disease is contraindicated.
- Case series Ashwagandha as a cause for liver injury (2020) Five liver-injury cases with a mixed or cholestatic pattern and prolonged jaundice, resolving in the reported cases.
- Monograph LiverTox: Ashwagandha, NCBI Bookshelf (2024) NIH hepatotoxicity monograph listing ashwagandha as a likely cause of clinically apparent liver injury.
- Systematic review Biopsychological effects of Ashwagandha in athletes and healthy individuals: systematic review (2025) Overview of 11 systematic reviews, 151 original studies, n=9005. Signals across endurance, strength, anxiety, sleep and sexual function with explicit caution on evidence limits.
- Meta-analysis The effects of L-theanine consumption on sleep outcomes: systematic review and meta-analysis (2025) 19 articles, 897 participants. Subjective sleep onset latency, daytime dysfunction and overall quality improved. Objective sleep measures were less convincing.
- Systematic review Examining the effect of L-theanine on sleep: systematic review of dietary supplementation trials (2026) 13 eligible trials, n=550. 200 to 450 mg/day supported sleep quality, latency, maintenance and efficiency more than total sleep time. Industry conflict noted.
- Meta-analysis L-theanine and cognitive performance: systematic review and meta-analysis of randomized placebo-controlled trials (2025) 5 RCTs, n=148 healthy adults. Dose-dependent reaction-time benefit on rapid visual information processing, with no significant effect on simple reaction time or Stroop.
- RCT L-theanine in the adjunctive treatment of generalized anxiety disorder: double-blind randomised placebo-controlled trial (2019) Did not clearly improve anxiety severity versus placebo as an add-on, though some insomnia and sleep-related outcomes improved. The honest null on L-theanine's anxiety score.
- RCT Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults (2019) Small crossover RCT improving stress-related symptoms and some anxiety, depression and sleep-related self-report measures.
- RCT L-theanine, a natural constituent in tea, and its effect on mental state (2008) Alpha-band EEG and relaxed-attention evidence at 50 mg, not the 200 mg often quoted for the alpha effect.
- RCT The combined effects of L-theanine and caffeine on cognitive performance and mood (2008) The combination improved attention switching and reduced susceptibility to distraction in memory tasks.
- RCT The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness (2010) Improved task-switching accuracy, subjective alertness and tiredness outcomes.
- Meta-analysis Acute effects of tea constituents L-theanine, caffeine and EGCG on cognitive function and mood: systematic review and meta-analysis (2014) Supports combined caffeine plus L-theanine effects on alertness and attentional switching accuracy in the first one to two hours.
- RCT The effects of L-theanine on objective sleep quality in boys with ADHD: randomized double-blind placebo-controlled trial (2011) Pediatric ADHD sleep RCT improving some objective sleep-quality measures with good tolerability. The only pediatric trial on either side.
- Regulatory FDA GRAS Notice No. 209, L-theanine (2026) FDA had no questions for specified food-category uses up to 250 mg per serving. A safety and food-use signal, not an efficacy endorsement.
Glossary
Quick reference for the medical and technical terms used in this comparison.
- HPA axis Hypothalamic-Pituitary-Adrenal Axis
- The hormone loop running the stress response and ending in cortisol. Ashwagandha damps it, which is why it takes weeks and why it reaches beyond the brain.
- Alpha waves Alpha-Band EEG Activity
- The 8 to 12 Hz brain rhythm associated with relaxed alertness. Nobre 2008 measured L-theanine raising it at 50 mg, which is the physiological basis for its flow-state score.
- HAM-A Hamilton Anxiety Rating Scale
- The standard clinician-rated anxiety scale. It is the endpoint Fatima 2024 and Bachour 2025 pooled across ashwagandha trials.
- PSS Perceived Stress Scale
- A self-report stress questionnaire. Bachour 2025 found it fell alongside cortisol at eight weeks on ashwagandha, which is the pairing that matters.
- GABA-A Gamma-Aminobutyric Acid Type A Receptor
- The main inhibitory receptor in the brain. Both compounds touch it, which is the one place their mechanisms overlap and why both list sedatives as an interaction.
- KSM-66 KSM-66 Ashwagandha
- A standardized root-only withanolide extract used in most trials cited here. It is why third-party-tested extract costs $15 to $30 rather than the $5 to $15 of generic powder.
- RVIP Rapid Visual Information Processing
- A sustained-attention task. Matyus 2025 found L-theanine improved reaction time on it dose-dependently while leaving simple reaction time and Stroop unchanged.
- GRAS Generally Recognized as Safe
- An FDA food-ingredient status. Notice 209 covers L-theanine for specified food uses up to 250 mg per serving, which is a safety signal rather than an efficacy endorsement.
