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Mechanism of ActionKey BenefitsDosage & FormsIn the Singular FormulaSafety & PrecautionsScientific StudiesFrequently Asked Questions
L-Theanine

L-Theanine

Théanine · Theanine · γ-Glutamyléthylamide

Amino acidsSystemic inflammation

L-theanine is an amino acid from green tea, associated with a state of calm alertness. Its best-supported effect concerns attention: a meta-analysis of 31 randomised trials measures a shorter reaction time within the hour following a 200 mg intake, in healthy adults. On sleep, the data converge without being spectacular. Syntheses report easier sleep onset and rest rated as more restorative, on self-reported measures. On stress, the effect exists but stays modest, and the trials carrying it are of uneven quality. With age, sleep fragments and tolerance to mental load declines. Sustaining the balance between cognitive activation and recovery then becomes an increasingly relevant lever of neurological well-being.

Last updated: August 11, 2026

Mechanism of Action

L-theanine shares a structural kinship with glutamate, the brain's main excitatory chemical messenger. This resemblance allows it to interact with glutamate receptors without triggering excitation. It acts as a quiet modulator rather than an activator.

Laboratory work describes an action on the release of GABA (the main natural brake on nervous activity), serotonin and dopamine. These observations come from animal models and cell preparations: they illuminate the pathway without establishing it in humans.

The molecule crosses the barrier that protects the brain. In humans, what is measured is its effect on alpha brain waves. Electroencephalography detects a rise in this activity between 45 and 105 minutes after intake, from 50 mg upwards. Alpha waves accompany states of wakeful relaxation and take part in the mechanisms of selective attention.

Key Benefits

  • Strong

    A shorter reaction time after a single intake: a meta-analysis of 31 randomised trials, covering 1,168 participants, measures improved choice reaction time 30 to 60 minutes after 200 mg, in healthy adults. A second meta-analysis, covering 50 trials, finds the same effect for L-theanine on its own.

  • Moderate

    Sleep experienced as better: in 30 adults with no psychiatric illness, 200 mg per day for 4 weeks improved the self-reported sleep quality score, including time to fall asleep. A meta-analysis of 19 publications, covering 897 participants, finds the same self-reported measures.

  • Moderate

    A dampened stress response: a systematic review of 9 controlled trials places the window in which L-theanine may reduce stress at 200 to 400 mg per day, in adults placed under stressful conditions.

  • Moderate

    A dampened physiological reaction under mental pressure: in 12 adults, in a double-blind crossover design, 200 mg of L-theanine attenuated the rise in heart rate and salivary immunoglobulin A during a mental arithmetic task.

  • Moderate

    Attention and working memory after 50: in 50 adults aged 50 to 69, a single 100 mg intake shortened reaction time on an attention test and improved accuracy on a working memory task, in a randomised placebo-controlled trial.

  • Moderate

    Verbal fluency and executive function: in the same 4-week trial at 200 mg per day, verbal fluency and executive function scores improved, with the fluency gain concentrated in participants whose baseline scores were lowest.

Dosage & Forms

Three production routes coexist on the market. Chemical synthesis by acylation delivers an isolated molecule at low cost. Enzymatic synthesis (the Suntheanine® process) produces the L-isomer exclusively, at a higher cost. Extraction starts from the green tea leaf, where L-theanine accounts for only 1 to 3% of dry matter: the aqueous extract concentrates it, then standardises it by HPLC assay, lot after lot.

The form of intake does not change exposure. A crossover trial in 12 participants compared 100 mg of L-theanine in isolated form with the same amount delivered through green tea. Plasma concentrations are comparable, the peak occurs at 0.8 hours, and the area under the curve rises in proportion to the dose between 50 and 200 mg.

Clinical trials place the retained effects between 100 and 400 mg. Reaction time is measured 30 to 60 minutes after a single 200 mg intake. Systematic reviews put the useful window at 200 to 450 mg per day for sleep, and 200 to 400 mg for stress.

In the Singular Formula

Inclusion rationale

Non-proteinogenic amino acid found almost exclusively in tea leaves (Camellia sinensis), where it represents up to 50% of free amino acids. It is L-theanine that gives green tea its distinctive umami character. Structurally analogous to glutamate, it has been studied since the 1960s in Japan. L-theanine crosses the blood-brain barrier and reaches the brain approximately 30 minutes after oral ingestion. Electroencephalographic studies show that it promotes the production of alpha waves (8-13 Hz), a brain state associated with wakeful relaxation and calm focus. This state of serene alertness, between drowsiness and mental hyperactivity, is precisely what individuals facing sustained cognitive demands seek. Several controlled trials have also explored its influence on sleep quality, with results suggesting improvement in sleep onset and subjective perception of rest. Its safety profile is firmly documented by decades of consumption through tea, and supplementation studies report no significant side effects at usual doses.

Selected form

Aqueous extract of green tea leaves (Camellia sinensis L.), standardised to a minimum of 40% L-theanine (HPLC). L-theanine is a non-proteinogenic amino acid, meaning it does not form part of the body's proteins. In nature, it is found almost exclusively in tea leaves. Extraction uses water alone, with no hexane, and concentrates 25 kg of leaves into 1 kg of extract. The theanine obtained is therefore the plant's own: no synthetic theanine is added. The remaining 60% is the natural green tea matrix, around 18% catechins (including 3 to 6% EGCG) and 0.3% caffeine. The leaves are harvested in China.

Formula dosage

0 to 200 mg.

Dose expressed as active substance, excluding excipients and carriers of the raw material.

Synergies in the formula

L-theanine pairs with several bioactives in the Singular formula through complementary pathways. Magnesium contributes to normal muscle function. It also contributes to normal psychological function. Combined with L-theanine, it covers two distinct physiological registers. Magnesium acts on muscle and psychological balance, L-theanine on brain activity and the transition to rest. Glycine acts through another mechanism. Laboratory work attributes to it a lowering of core body temperature, a physiological signal for sleep onset. Paired with L-theanine, it covers both the thermal and the neuronal side of preparing for rest. Vitamin B6 (P5P) acts as a cofactor in the synthesis of serotonin and GABA, the two chemical messengers on which laboratory work locates L-theanine's action. Adequate vitamin B6 intake supports the availability of these neurotransmitters. Taurine shares with L-theanine an affinity for receptors involved in the regulation of nervous excitability, described in laboratory work.

Safety & Precautions

L-theanine benefits from a considerable history of use: tea, its near-exclusive dietary source, has been consumed for millennia. The largest meta-analysis, covering 31 randomised trials, reports no serious adverse events. Trials have explored up to 900 mg per day over two months. Beyond three months, data are lacking.

One trial recorded a rise in headache ratings at 250 mg taken on its own. No major drug interaction is established. As a precaution, individuals taking antihypertensives or sedatives are advised to consult a healthcare professional.

The green tea extract also delivers 90 mg of catechins, including 15 to 30 mg of epigallocatechin gallate. On that basis, it is not advised to take it on an empty stomach, or on the same day as other green tea products.

Supplementation is not advised during pregnancy or breastfeeding, for want of human data: in animals, theanine crosses the placenta and appears in milk. It is intended for adults only.

Scientific Studies

AuthorsYearTypeJournal

Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials

Systematic review and meta-analysis of 31 randomised trials, 1,168 participants. A single 200 mg dose, 30 to 60 minutes before testing, improved choice reaction time. The authors describe the reduction in acute stress as modest and largely driven by trials at high risk of bias; anxiety effects are inconsistent and non-significant, and no effect is found on fatigue. No serious adverse events are reported.

The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis

Systematic review and meta-analysis of 19 publications, 897 participants. Significant improvement in self-reported sleep onset latency, daytime dysfunction and overall sleep quality score. The authors note that few trials use L-theanine on its own, and call for work on the useful dose and duration.

Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials

Systematic review restricted to trials where L-theanine is given on its own: 13 trials, 550 participants, from 50 to 900 mg per day. The authors conclude that 200 to 450 mg per day is a safe and effective way to support sleep in adults, on both objective and self-reported measures, and call for trials in people with clinical insomnia.

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

Fifty randomised trials, fifteen meta-analysed. L-theanine on its own improves choice reaction time in the first hour. The combination with caffeine mainly improves accuracy on attentional tasks in the second hour. Two caveats from the authors: no included trial is at low risk of bias, and the review is funded by a tea manufacturer.

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial

Randomised, crossover, double-blind trial in 30 adults with no major psychiatric illness, mean age 48. At 200 mg per day for 4 weeks, sleep quality, trait anxiety and depressive mood scores fell, as did the sleep latency and sleep disturbance subscores. Verbal fluency and executive function improved. No effect on cortisol or immunoglobulin A, in saliva or serum.

Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study

Randomised placebo-controlled trial in 50 analysed adults aged 50 to 69, at 100.6 mg of theanine. A single intake shortened Stroop test reaction time and improved accuracy on a working memory task. The authors state that after 12 weeks of regular intake, theanine had no effect on attention-related processes.

L-Theanine reduces psychological and physiological stress responses

Double-blind crossover trial in 12 participants, four sessions each. At 200 mg, L-theanine attenuated the rise in heart rate and salivary immunoglobulin A induced by a mental arithmetic task. Heart rate variability analysis attributes the effect to reduced sympathetic activation. Cortisol was not measured.

The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review

Systematic review of 9 controlled trials in which L-theanine is taken as a supplement, compared with a control. The authors conclude that 200 to 400 mg per day may help reduce stress and anxiety in people exposed to stressful conditions, and call for longer studies in larger cohorts.

Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea

Randomised crossover trial in 12 participants receiving 100 mg of L-theanine in isolated form, then through green tea. Plasma, erythrocyte and urinary concentrations are comparable between the two forms, with a peak at 0.8 hours. The area under the curve rises in proportion to the dose between 50 and 200 mg. This is the only direct human comparison between the two forms of intake.

L-theanine, a natural constituent in tea, and its effect on mental state

Electroencephalography in healthy young adults, resting with eyes closed, at baseline and 45 to 105 minutes after 50 mg of L-theanine or placebo. Alpha activity increased more under L-theanine, and a second protocol reproduced the effect during passive activity. The authors conclude there is an effect on the general state of alertness, at realistic dietary intake levels.

Frequently Asked Questions

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