Home Ingredients Suntheanine®
CognitiveSleep HealthStress & AnxietyMood & Mental Health

Suntheanine®

Camellia sinensis
Evidence Level
Strong
2 Clinical Trials
4 Documented Benefits
4/5 Evidence Score

Suntheanine® is a patented, 100% pure L-isomer theanine produced via an enzymatic process that mimics biosynthesis in green tea leaves — yielding a purity level impossible to achieve through standard tea extraction. With over 40 human clinical trials, it is the most researched form of L-theanine, specifically validated for promoting relaxed alertness, alpha brainwave induction, and caffeine synergy.

Studied Dose 50–200 mg/day; 100–200 mg for relaxation/focus; 50 mg for caffeine stacking
Active Compound L-theanine (≥98% L-isomer) — Suntheanine® by Taiyo International

Benefits

Alpha brainwave induction

Suntheanine increases alpha brain wave activity (8–13 Hz) within 30–60 minutes of ingestion, producing a measurable state of alert relaxation without sedation — distinct from other calming agents that suppress beta waves and cause drowsiness.

Supported by Trial 2

Caffeine synergy and jitter reduction

Clinical trials show Suntheanine combined with caffeine significantly improves sustained attention, accuracy on cognitive tasks, and reduces the jitteriness and blood pressure elevation associated with caffeine alone. The 1:2 ratio (theanine:caffeine) is the most studied combination.

Supported by Trial 1

Stress and anxiety reduction

Multiple RCTs demonstrate significant reductions in subjective stress, anxiety, and salivary cortisol with Suntheanine supplementation. Benefits extend to psychological and physiological stress markers without causing sedation.

Supported by Trial 2

Sleep quality improvement

When taken before bed, Suntheanine improves sleep quality without acting as a sedative — subjects wake feeling more refreshed rather than groggy. Particularly effective in individuals with high anxiety-driven sleep disruption.

Supported by Trial 2

Mechanism of action

1

GABA and glutamate modulation

L-theanine crosses the blood-brain barrier and modulates both inhibitory (GABA) and excitatory (glutamate, NMDA) neurotransmitter systems, simultaneously promoting relaxation and preventing over-excitation without sedation.

2

Alpha oscillation enhancement

Theanine selectively increases alpha-band (8–13 Hz) oscillatory activity in the occipital and parietal cortex, a brainwave frequency associated with relaxed, focused states — measurable by EEG within 45 minutes of ingestion.

3

Dopamine and serotonin regulation

Theanine influences dopamine and serotonin levels in specific brain regions, contributing to mood stabilization and cognitive enhancement effects without the receptor desensitization seen with direct agonists.

Clinical trials

1
L-Theanine + Caffeine and Cognitive Performance — Clinical Trial

Clinical trial examining cognitive and mood effects of L-theanine (97 mg) combined with caffeine (40 mg) vs. each alone and placebo in 27 young adults.

27 healthy young adults. Crossover design.

L-theanine + caffeine combination significantly improved speed and accuracy on attention-switching tasks and reduced susceptibility to distraction vs. placebo. Combination outperformed either alone for sustained attention.

2
Suntheanine and Stress in Healthy Adults — Clinical Trial

Clinical trial of Suntheanine (200 mg/day) vs. placebo in 30 adults with stress-related symptoms for 4 weeks.

30 healthy adults with stress-related symptoms. 4-week intervention.

L-theanine significantly improved letter fluency and depression subscale scores. Participants reported improved sleep quality and reduced stress. No adverse effects.

Side effects and drug interactions

Common Potential side effects

Very well tolerated at all studied doses up to 400 mg/day
Rare reports of mild headache at initiation
May enhance sedative effects of sleep medications — use caution if combining

Important Drug interactions

CNS stimulants (caffeine, ADHD medications) — theanine modulates stimulant effects; generally beneficial but monitor for unpredictable interactions at high doses
Antihypertensive medications — theanine may mildly lower blood pressure; additive effect possible
Sedatives and anxiolytics — theanine has mild calming effects; may potentiate CNS depressants

Featured in these supplement guides

Anxiety→Brain Fog→Sleep & Insomnia→

More Cognitive Ingredients

Energy
Caffeine
Caffeine, a natural stimulant found in coffee, tea, and other plants, is commonly suppleme…
Cardiovascular
Omega-3 Fatty Acids
Omega-3 fatty acids, primarily eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), an…
Cognitive
Vitamin B12
Vitamin B12, also known as cobalamin, is a water-soluble vitamin commonly supplemented as…
Immune Support
Zinc
Zinc, an essential trace mineral, is commonly supplemented in forms like zinc gluconate, a…

Explore Other Ingredients

Cognitive
Holy Basil (Tulsi)
Holy basil (tulsi) is a revered adaptogenic herb in Ayurvedic tradition, used to help the…
Energy
SalidroPure™ (Pure Salidroside)
SalidroPure™ is NNB Nutrition's precision-fermented pure salidroside — the primary bioacti…
Cognitive
Bacopa Monnieri
Bacopa monnieri (Brahmi) is a cornerstone herb in Ayurvedic medicine with over 3,000 years…

Frequently asked questions about Suntheanine®

What is Suntheanine?

Suntheanine® is a patented, 100% pure L-isomer theanine produced via an enzymatic process that mimics biosynthesis in green tea leaves — yielding a purity level impossible to achieve through standard tea extraction.

What is Suntheanine used for?

Suntheanine is researched primarily for Cognitive, Sleep Health, and Stress & Anxiety. Suntheanine increases alpha brain wave activity (8–13 Hz) within 30–60 minutes of ingestion, producing a measurable state of alert relaxation without sedation — distinct from other calming agents that suppress beta waves and cause drowsines…

What is the recommended dosage of Suntheanine?

The clinically studied dose is 50–200 mg/day; 100–200 mg for relaxation/focus; 50 mg for caffeine stacking Always follow the product label and check with a healthcare provider for personal advice.

Is Suntheanine safe, and does it have side effects?

For most healthy adults, Suntheanine is well tolerated at studied doses. Reported effects can include: Very well tolerated at all studied doses up to 400 mg/day Rare reports of mild headache at initiation It may also interact with some medications. Suntheanine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Suntheanine interact with any medications?

Possible interactions include: CNS stimulants (caffeine, ADHD medications) — theanine modulates stimulant effects; generally beneficial but monitor for unpredictable interactions at high doses Antihypertensive medications — theanine may mildly lower blood pressure; additive effect possible If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Suntheanine?

NutraSmarts rates the evidence for Suntheanine as Strong (4 out of 5). It is backed by 2 clinical trials and 4 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(4 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF 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;232(14):2563-2576. doi: 10.1007/s00213-015-3895-0.PubMedUsed to support: Uses Suntheanine (Taiyo) L-theanine, alone and with caffeine, examining attention, mood and cerebral blood flow. Honest framing: effects were modest and most apparent in combination with caffeine rather than from L-theanine alone.
  2. Williams J, McKune AJ, Georgousopoulou EN, Kellett J, D'Cunha NM, Sergi D, et al. The Effect of L-Theanine Incorporated in a Functional Food Product (Mango Sorbet) on Physiological Responses in Healthy Males: A Pilot Randomised Controlled Trial. Foods. 2020;9(3):371. doi: 10.3390/foods9030371.PubMedUsed to support: A pilot RCT delivering Suntheanine (Taiyo Kagaku) and measuring relaxation-related physiological responses such as heart-rate and blood-pressure measures. Honest framing: a small pilot with limited and preliminary effects.
  3. Halson SL, Shaw G, Versey N, Miller DJ, Sargent C, Roach GD, et al. Optimisation and Validation of a Nutritional Intervention to Enhance Sleep Quality and Quantity. Nutrients. 2020;12(9):2579. doi: 10.3390/nu12092579.PubMedUsed to support: Uses Suntheanine (dose-finding 500-1000 mg) within a sleep-promoting nutritional intervention. Honest framing: L-theanine was one component of a multi-ingredient formula, so a specific Suntheanine sleep effect cannot be isolated; effects were modest.
  4. Kimura K, Ozeki M, Juneja LR, Ohira H L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39-45. doi: 10.1016/j.biopsycho.2006.06.006.PubMedUsed to support: A controlled crossover study using Suntheanine (Taiyo) showing L-theanine blunted heart-rate and salivary stress-marker (sIgA) responses to an acute mental-arithmetic stressor, supporting the calm-without-sedation claim. Honest framing: a small acute-stress laboratory study, not a long-term clinical outcome trial.