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Suntheanine L-Theanine 125 mg

Natural Factors Stress-Relax
4.7
★ ★ ★ ★ ★
(1515 ratings)
Theanine 250 mg
Product Image
Score84
A strong branded-theanine option with substantial dosing, though the per-unit versus full-serving presentation needs attention.
How scoring works
Quantity:60 Capsule(s) • (30 servings)
Goals:
Stress Relief
Productivity Boost
Cognitive Support
Sleep Support
Mental Focus
Brain Health
Mood Support

Score 84

A strong branded-theanine option with substantial dosing, though the per-unit versus full-serving presentation needs attention.
How scoring works
$18.87($0.62 per serving)
iHerb
$ 18.87
Amazon
$ 18.87
Vitacost
$ 18.87
Report prices

Analysis

The serving provides a substantial amount of branded Suntheanine. It is well suited to calm focus, situational stress, and pre-sleep relaxation.

The product name emphasizes a smaller unit amount than the full serving, so users need to check how many capsules they take. The formula remains narrow and does not cover broader memory or sleep-maintenance pathways.

Branded sourcing supports confidence in the L-isomer identity. Practical value is competitive despite the premium ingredient.

Who is it for
  • Adults wanting branded Suntheanine
  • Users seeking substantial calm-focus support
  • People comfortable with multi-capsule serving directions
Best for
  • Stress-related tension
  • Calm focus
  • Pre-sleep relaxation

Pros

  • Branded Suntheanine
  • Substantial preferred-range serving
  • Strong source identity
  • Competitive value

Cons

  • Per-unit amount can be confusing
  • Narrow single-active formula
  • Upper-range serving may be too relaxing for some
  • No broader cognitive ingredients

Warnings

  • The full serving may cause drowsiness in sensitive users
  • Sedatives or alcohol may increase sleepiness
  • People using antihypertensive medicine should watch for lightheadedness

Nutrient quality

95 Highest impact

Suntheanine provides strong ingredient identity and purity assurance. The disclosed amount is substantial and well aligned with calm-focus use.

.

Ingredient transparency

84 Highest impact

Every listed active has a specific amount, which makes the core formula straightforward to assess. The supplied data omits a complete excipient list and full intake directions.

.

Customer satisfaction

70 High impact

The supplied aggregate satisfaction signal is favorable. A large amount of feedback makes that aggregate signal reasonably stable, but no narrative evidence was provided.

.

Value for money

85 Highest impact

The branded source and substantial amount support the premium positioning. Serving-level value is fair rather than exceptional for a single active.

.
Report analysis

Goals

Stress Relief
Stress Relief
Impact
Highest effect
A Goal FitA+ Strength of SupportC+ CoverageA Formula Quality
Theanine · 250 mg

Branded L-theanine is well aligned with calm focus and may reduce acute feelings of stress without acting as a conventional sedative. The fully disclosed amount sits in a strong range for this purpose.

Suntheanine provides a useful purity and standardization signal. The single-ingredient approach offers excellent depth for mental calm but does not address cortisol regulation or foundational mineral support.

Study evidence
Theanine Supportive 16 studies
Productivity Boost
Productivity Boost
Impact
Highest effect
A- Goal FitA+ Strength of SupportC- CoverageA+ Formula Quality
Theanine · 250 mg

Branded L-theanine may support calm attention and reduce distraction from tension. The disclosed amount sits within a well-used range for relaxed focus.

Suntheanine provides strong purity and identity assurance. The single active is focused, although evidence for sharper performance is stronger when theanine is paired with caffeine.

Study evidence
Theanine Supportive 5 studies
Cognitive Support
Cognitive Support
Impact
Highest effect
B Goal FitA+ Strength of SupportD+ CoverageA Formula Quality
Theanine · 250 mg

Suntheanine provides a well-characterized L-theanine form for calm attention. The 250 mg amount reaches the upper end of the preferred range.

Used alone, L-theanine offers a gentler cognitive effect than a broader focus stack. Branded sourcing, full disclosure, and a streamlined formula provide strong depth in one pathway.

Study evidence
Theanine Supportive 25 studies
Sleep Support
Sleep Support
Impact
Highest effect
B Goal FitA Strength of SupportC CoverageA+ Formula Quality
Theanine · 250 mg

Suntheanine L-theanine at 250 mg provides a well-disclosed, branded relaxation ingredient at a substantial amount. It may help quiet mental arousal, though its sleep evidence is less direct than melatonin.

The single-active formula has good depth but covers no circadian or mineral pathway. Its streamlined design is coherent for people whose sleep difficulty is linked to feeling mentally wound up.

Study evidence
Theanine Supportive 8 studies
Mental Focus
Mental Focus
Impact
Highest effect
B+ Goal FitB+ Strength of SupportD+ CoverageA+ Formula Quality
Theanine · 250 mg

Suntheanine offers a well-identified L-theanine source for calm attention and stress-related concentration. The supplied facts conflict on serving size and active amount, which makes the actual intake less certain.

The listed 250 mg amount would be substantial if it applies to the intended serving. No caffeine or other alertness ingredient is included, so the formula remains limited to a calming pathway.

Study evidence
Theanine Supportive 19 studies
Brain Health
Brain Health
Impact
Highest effect
B- Goal FitA+ Strength of SupportD+ CoverageA+ Formula Quality

Branded L-theanine may support calm focus and mental composure with strong ingredient-quality assurance. Its role remains narrow and does not cover structural brain health or several cognitive pathways.

The 250 mg amount is clearly disclosed at the upper end of the preferred range. Suntheanine supplies a standardized branded source with strong purity confidence.

Study evidence
Theanine Supportive 17 studies
Mood Support
Mood Support
Impact
High effect
C Goal FitA+ Strength of SupportD CoverageA+ Formula Quality

L-theanine may reduce tension and support a calmer emotional state without strong sedation. Evidence is useful for short-term stress responses but less established for persistent low mood.

The 250 mg amount is clearly disclosed and uses branded Suntheanine with strong purity assurance. The single-ingredient design is focused but covers only one mood-related pathway.

Study evidence
Theanine Supportive 12 studies

Ingredients

IngredientAmount per serving
Suntheanine L-Theanine
250 mg
Gluten Free Adults 18–50 Vegan Dairy Free Sugar Free Vegetarian
Report overview
Theanine · 250 mg OverallScore96
A+ Active Ingredient Quality & BioavailabilityA+ Dose, Safety & Label TransparencyB+ Value

Suntheanine supplies a branded, high-purity L-theanine form with strong isomer confidence. The disclosed 250 mg amount sits at the upper end of the preferred range for calm focus. Its cost per active amount remains competitive despite premium branded sourcing.

View ingredientView products
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87 Performance

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<p>200 mg of clearly stated L-theanine is paired with favorable serving-level value in the supplied data. The ingredient profile remains focused on theanine and offers a practical alternative to the original formula.</p>
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<p>100 mg of clearly stated L-theanine is paired with favorable serving-level value in the supplied data. The ingredient profile remains focused on theanine and offers a practical alternative to the original formula.</p>
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Sources

Published studies used for the product analysis and the top-ranked studies for each ingredient and goal.

  1. The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.
    Bulman A; D'Cunha NM; Marx W; Turner M; McKune A; Naumovski N · Sleep medicine reviews · 2025
    Meta-analysis897 participants19 studies pooledSleep Support forTheanine
  2. Comparison Between Efficacy of Oral Melatonin and Oral L-theanine in Improving Sleep in Cancer Patients Suffering From Insomnia: A Randomised Double-blinded Placebo-controlled Study.
    Kurdi MS; As A; Ladhad DA; Mitragotri MV; Baiju A · Indian journal of palliative care · 2024
    Randomized trial120 participantsSleep Support forTheanine
  3. Current Evidence on Common Dietary Supplements for Sleep Quality.
    Esquivel MK; Ghosn B · American journal of lifestyle medicine · 2025
    Narrative reviewSleep Support forTheanine
  4. In Search of a Safe Natural Sleep Aid.
    Rao TP; Ozeki M; Juneja LR · Journal of the American College of Nutrition · 2016
    Narrative reviewSleep Support forTheanine
  5. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.
    Hidese S; Ogawa S; Ota M; Ishida I; Yasukawa Z; Ozeki M; Kunugi H · Nutrients · 2020
    Randomized trial30 participantsSleep Support Brain Health Cognitive Support forTheanine
  6. The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.
    Williams JL; Everett JM; D'Cunha NM; Sergi D; Georgousopoulou EN; Keegan RJ; McKune AJ; Mellor DD; Anstice N; Naumovski N · Plant foods for human nutrition (Dordrecht, Netherlands) · 2020
    Systematic review9 studies pooledStress Relief Mood Support forTheanine
  7. A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave® L-Theanine on Stress in a Healthy Adult Population.
    Evans M; McDonald AC; Xiong L; Crowley DC; Guthrie N · Neurology and therapy · 2021
    Randomized trialStress Relief Brain Health forTheanine
  8. Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial.
    White DJ; de Klerk S; Woods W; Gondalia S; Noonan C; Scholey AB · Nutrients · 2016
    Randomized trial34 participantsStress Relief forTheanine
  9. L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial.
    Sarris J; Byrne GJ; Cribb L; Oliver G; Murphy J; Macdonald P; Nazareth S; Karamacoska D; Galea S; Short A; Ee C; Birling Y; Menon R; Ng CH · Journal of psychiatric research · 2020
    Randomized trial46 participantsStress Relief Sleep Support forTheanine
  10. Effect of Combined Ingestion of L-Theanine and L-Arginine for Short-Term Psychological Stress in Young Adults: A Randomized Placebo-Controlled Study.
    Furushima D; Sugiyama I; Nomura Y; Unno K; Yamada H · Journal of nutritional science and vitaminology · 2023
    Randomized trial120 participantsStress Relief forTheanine
  11. Promising, but Not Completely Conclusive-The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Trials.
    Mátyus RO; Szikora Z; Bodó D; Vargáné Szabó B; Csupor É; Csupor D; Tóth B · Journal of clinical medicine · 2025
    Meta-analysis148 participants5 studies pooledMental Focus forTheanine
  12. Acute effects of theanine, caffeine and theanine-caffeine combination on attention.
    Kahathuduwa CN; Dassanayake TL; Amarakoon AMT; Weerasinghe VS · Nutritional neuroscience · 2018
    Clinical trial20 participantsMental Focus Cognitive Support forTheanine
  13. L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.
    Dassanayake TL; Kahathuduwa CN; Weerasinghe VS · Nutritional neuroscience · 2022
    Randomized trial27 participantsMental Focus forTheanine
  14. Dose-response effect of L-theanine on psychomotor speed, sustained attention, and inhibitory control: a double-blind, placebo-controlled, crossover study.
    Dassanayake TL; Wijesundara D; Kahathuduwa CN; Weerasinghe VS · Nutritional neuroscience · 2023
    Randomized trial32 participantsMental Focus Cognitive Support forTheanine
  15. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together.
    Rogers PJ; Smith JE; Heatherley SV; Pleydell-Pearce CW · Psychopharmacology · 2008
    Randomized trial48 participantsMental Focus Productivity Boost forTheanine
  16. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.
    Payne ER; Aceves-Martins M; Dubost J; Greyling A; de Roos B · Nutrition reviews · 2025
    Meta-analysis50 studies pooledBrain Health Cognitive Support Mental Focus forTheanine
  17. Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task.
    Foxe JJ; Morie KP; Laud PJ; Rowson MJ; de Bruin EA; Kelly SP · Neuropharmacology · 2012
    Randomized trial27 participantsBrain Health Cognitive Support forTheanine
  18. Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study.
    Baba Y; Inagaki S; Nakagawa S; Kaneko T; Kobayashi M; Takihara T · Journal of medicinal food · 2021
    Randomized trialBrain Health Mental Focus Productivity Boost forTheanine
  19. Safety and Efficacy of AlphaWave® L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial.
    Moulin M; Crowley DC; Xiong L; Guthrie N; Lewis ED · Neurology and therapy · 2024
    Randomized trial30 participantsMental Focus Productivity Boost Stress Relief forTheanine
  20. Effect of L-theanine on selective attention in a traffic-related reaction task in sleep-deprived young adults: a double-blind placebo-controlled, crossover study.
    Karunaratne UW; Dassanayake TL · Nutritional neuroscience · 2025
    Randomized trial24 participantsMental Focus forTheanine
  21. l-theanine adjunct to sertraline for major depressive disorder: A randomized, double-blind, placebo-controlled clinical trial.
    Shamabadi A; Kafi F; Arab Bafrani M; Asadigandomani H; A Basti F; Akhondzadeh S · Journal of affective disorders · 2023
    Randomized trial60 participantsMood Support forTheanine
  22. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study.
    Ritsner MS; Miodownik C; Ratner Y; Shleifer T; Mar M; Pintov L; Lerner V · The Journal of clinical psychiatry · 2011
    Randomized trial60 participantsMood Support Stress Relief forTheanine
  23. Comparison of the effects of two amino acids, Gamma-aminobutyric acid (GABA) and L-theanine, on sedation, anxiety, and cognition in preoperative surgical patients - A randomized controlled study.
    Deshpande SS; Kurdi M; Baiju A; Athira AS; Sarasamma AG; Gangadharan AK · Journal of anaesthesiology, clinical pharmacology · 2025
    Randomized trial168 participantsMood Support Stress Relief forTheanine
  24. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stress.
    Unno K; Tanida N; Ishii N; Yamamoto H; Iguchi K; Hoshino M; Takeda A; Ozawa H; Ohkubo T; Juneja LR; Yamada H · Pharmacology, biochemistry, and behavior · 2014
    Randomized trial20 participantsMood Support forTheanine
  25. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.
    Gerolymos C; Saddier E; Boyer L; Fond G · Molecular psychiatry · 2026
    Meta-analysis1,168 participants31 studies pooledProductivity Boost forTheanine
  26. Effects of L-theanine on cognition, mood and sleep: evidence from human trials.
    Cotter J; Kilpatrick HE · Frontiers in nutrition · 2026
    Narrative reviewProductivity Boost forTheanine