L-Theanine

We evaluated 120 human studies on L-Theanine, including 60 randomised controlled trials and 16 meta-analyses or systematic reviews; the controlled studies include 3,180 participants in total. As of 11 October 2026.

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1. What Is L-Theanine? Occurrence, Origin and Forms

L-theanine is an amino acid that occurs naturally in the leaves of the tea plant (Camellia sinensis) and has also been detected in some edible mushrooms. It is not one of the building blocks of proteins and is studied mainly as a pure substance. Traditionally it is associated with the calm, alert state that follows drinking tea.

In nature it occurs in the leaves and buds of the tea plant and in a few mushroom species. As a pure substance it appears in capsules, powders and beverages.

For research, L-theanine is extracted from tea leaves or produced microbially and used as a pure substance with a defined content. Studies examine capsules and powders, theanine-containing plant extracts, and combinations with caffeine.

Forms and Preparations Studied

• L-theanine as a pure substance (capsule or powder)
• D-theanine and racemic theanine
• Theanine-containing tea or plant extract
• Theanine combined with caffeine
• Theanine-containing beverages

Not covered on this page:

• Theophylline and theobromine — related purine alkaloids from tea and cocoa, but different substances
• Caffeine on its own
• Other amino acids described as calming, such as glycine, taurine or GABA
• Green tea extracts in which ingredients other than theanine form the difference between the groups

2. What Does L-Theanine Do? Results by Area

How to read the table: counted are human studies whose results concern the area. “High” means at least one meta-analysis and two controlled studies showing improvement, or at least three controlled studies of which three quarters show improvement, with at least 300 participants in total. “Moderate” means at least two controlled studies showing improvement, as a majority, or one meta-analysis alongside controlled studies. “Low” means one controlled study showing improvement. Where an area has no controlled study, the strength of evidence is at most “low” (result “reviews only” or “observational data only”). Everything else is “unclear”. A study counts as showing improvement when at least half of its outcomes in this area improved. Reviews of combination products do not count as meta-analyses; results that only describe side effects or shares of users do not count as an effect. The same study is counted only once.

3. What the Studies Show in Detail

L-Theanine, Cognition and Attention: Human Studies

L-theanine was studied predominantly as a pure substance in capsule or powder form, mostly as a single dose. A meta-analysis found a faster choice reaction time after a single dose than under placebo 1. Individual studies showed faster reactions in the Stroop test 52 and with simple stimuli 57, another meta-analysis found no difference there 4. In a crossover study in healthy adults, executive function and verbal fluency improved after L-theanine, not after placebo 4054. A randomized controlled trial with matcha, which contains caffeine and catechins in addition to L-theanine, found faster reactions in the Stroop test after mild stress than under placebo 35. Reviews attribute the most pronounced attention effects to the combination with caffeine or green tea; they do not belong to L-theanine alone 101314. A randomized controlled trial with a nutrient-enriched breakfast bar containing L-theanine, α-linolenic acid, L-tyrosine, vitamins, minerals and caffeine found better attention, working and episodic memory as well as executive function 24. Many studies tested only single doses over short periods; the study on executive function was manufacturer-funded 54.

Further studies in this area: 39 40 41 46 47 52 56 57 59 61 63 69 70 75 76 84 85 86 93 94 95

L-Theanine, Stress and Tension: Human Studies

Compared with placebo, L-theanine as an add-on to antipsychotic therapy reduced anxiety in schizophrenia 31 and, in female archers, competition anxiety 64. Before operations, in one study without a placebo group, it had an anxiety-relieving effect and was less sedating than alprazolam 19. In a crossover study in healthy individuals, anxiety and depression scores decreased only after L-theanine, but a confirmed group difference was not reported for this 4054. A systematic review on the pure substance considers a reduction in stress under load possible 11. A meta-analysis found a small reduction in acute stress supported by error-prone studies and no consistent effect on anxiety 1. A controlled study found no differences in salivary alpha-amylase, secretory IgA, heart rate and State-Trait Anxiety Inventory during a stress exercise 26. In generalized anxiety disorder, L-theanine as an add-on therapy did not reduce anxiety more than placebo 34. The form tested was predominantly L-theanine as a pure substance in capsule or powder form.

Further studies in this area: 40 44 53 64 65 67 73 74 75 76 83 84 86 90 91 92

L-Theanine, Sleep and Sleep Quality: Human Studies

In boys with ADHD, L-theanine improved sleep efficiency compared with placebo, but not sleep onset latency 23. In healthy adults, sleep onset latency and sleep disturbances improved more than under placebo in the sleep questionnaire 40. In anxiety disorder, sleep satisfaction increased more than under placebo, the severity of insomnia did not differ 34. Under an L-theanine preparation, light sleep decreased compared with placebo, but so did sleep duration 39. A systematic review on the pure substance overall assesses the studies as an indication of better sleep 3. A mixed preparation of L-theanine, lemon balm, valerian and saffron did not differ from placebo in sleep efficiency, total sleep time, wake time after sleep onset and PSQI 2728. A mixture of L-theanine and casein hydrolysate prolonged sleep duration and sleep efficiency compared with placebo 38. With Lactium and L-theanine, sleep quality and insomnia scores did not differ from placebo, only individual diary values 36. Of two preparations with L-theanine, hemp-based cannabinoids, botanical oils and GABA, only the one containing THC improved sleep disorder compared with placebo 17. The form tested was mostly L-theanine as a capsule or tablet, alongside theanine-containing beverages and extracts.

Further studies in this area: 50 68 75 76 77 78 79 84 87 88 92

L-Theanine, Mood and Relaxation: Human Studies

As an add-on to sertraline, L-theanine in depression improved symptoms as well as response and remission more than placebo 29. A meta-analysis found after a single dose in healthy individuals fewer depressive symptoms than under placebo, after excluding a divergent study 1. At rest, a controlled study showed indications of a relaxing effect, under artificially induced anxiety neither L-theanine nor alprazolam had an anxiolytic effect 65. Another found after a cognitive task less tension than under placebo 66. Mixtures with L-theanine improved mood scores only compared with baseline or as an uncertain trend: a chamomile beverage 48, matcha with catechins and caffeine 49 and a fat spread with 5-hydroxytryptophan and GABA 51. There was no difference from placebo in mood under matcha as a beverage or bar 42 and in depression scores under L-theanine in addition to risperidone 30. The findings come predominantly from small, short studies, partly in patient groups. Further investigations tested mixtures with caffeine 5, green tea constituents 6, cannabinoids and GABA 17 as well as vitamins, L-tyrosine and caffeine 24; their findings do not belong to L-theanine alone.

Further studies in this area: 75 76 84 86

L-Theanine and Theanine Combined with Caffeine: Human Studies

In two small crossover studies, the combination of L-theanine and caffeine accelerated the reaction to target stimuli, but L-theanine alone did as well 4663. A randomized controlled study also found lower tension in a social stress situation when L-theanine was given together with caffeine instead of caffeine alone 33. In contrast, a controlled study found no difference of the combination compared with placebo in global visual attention and in conflict processing, because the opposing effects of both substances canceled each other out 56. A meta-analysis saw advantages of the combination especially in alertness and attention switching; the caffeine dose seemed to matter more than the theanine dose 15.

Further studies in this area: 55 56 60 62 63 68 69 95

L-Theanine, Blood Pressure and Cardiovascular Function: Human Studies

For blood pressure and cardiovascular health, the evidence is limited: a controlled study (not randomized) with L-theanine as the pure substance found after a mental task a lower blood pressure increase, but only in strongly reacting individuals 66. A randomized controlled study with L-theanine as the pure substance in a food matrix (mango sorbet), by contrast, found no difference in systolic and diastolic blood pressure, heart rate and heart rate variability 45. Both studies were very small and short; the form tested was in each case L-theanine as the pure substance, once in a food matrix. It remains open whether the findings can be confirmed in larger groups, longer administration and other preparations.

L-Theanine: Further Outcomes in Studies

As an add-on to antipsychotic therapy, L-theanine in two placebo studies in schizophrenia improved individual PANSS scores 3031; a secondary analysis linked the improvement to BDNF and the cortisol-DHEAS ratio 37. The findings come from small, short add-on studies; since both groups received the antipsychotics, the difference is attributable to L-theanine.

Further studies in this area: 58 71 72 73 74 79 80 81 82 84 85 89 92 93

4. How Is L-Theanine Dosed? Preparation, Dose and Duration in Studies

The studies tested predominantly L-theanine as a pure substance in capsule, powder or chewable tablet form, sometimes in a food matrix such as sorbet. In addition, theanine-containing beverages such as matcha, theanine-containing extracts and fixed combinations with caffeine were used. Individual investigations gave L-theanine in addition to an ongoing drug treatment.

5. Is L-Theanine Safe? Side Effects in Studies

In the studies, L-theanine was predominantly well tolerated; serious adverse events were not reported 131. As an add-on to antipsychotics or sertraline, side effects in controlled studies did not differ from placebo 293031.

6. What Remains Open: Limits of the Evidence

• Many studies tested only single doses over short periods and in small groups.
• The effect with longer use and in larger groups is open.
• Individual studies with positive results were manufacturer-funded.
• For mixed preparations with caffeine or other substances, the contribution of L-theanine alone cannot be distinguished.
• For blood pressure and heart rate, the evidence is limited and rests on very small, short studies.

7. Bottom Line: What Is Established About L-Theanine

L-theanine is an amino acid that occurs naturally in tea leaves and has been tested in studies predominantly as a pure substance.

A faster reaction time after L-theanine as a pure substance is best supported 15257. Compared with placebo, individual sleep measures also improved 2340 and, as an add-on to medications, anxiety in schizophrenia 31 as well as depression 29. In two small studies, L-theanine accelerated reaction alone as well as combined with caffeine 4663. For blood pressure and heart rate, the evidence is limited: one controlled study found a smaller rise in blood pressure after a mental task only in highly reactive individuals 66, a randomized controlled study found no difference 45. Next, it would need to be clarified whether the findings on sleep and anxiety can be confirmed in larger and longer placebo studies.