L-Theanine Simply Explained

1. What Is L-Theanine?

L-theanine is an amino acid. It occurs naturally in the leaves of the tea plant. It has also been detected in some edible mushrooms. It is not one of the building blocks of proteins. In studies it is mostly tested as the pure substance. Traditionally it is associated with the calm, alert feeling after drinking tea.

2. Where Is It Found, and What Is It Made From?

Naturally, L-theanine is found in the leaves and buds of the tea plant. It also occurs in individual mushroom species. As a pure substance it is available in capsules, powders and beverages. For studies it is obtained from tea leaves or produced microbially. Capsules, powders, plant extracts and mixtures with caffeine are tested.

3. What Does L-Theanine Do? What Research Shows

Cognition and Attention

The best-supported finding is a faster reaction after L-theanine as a pure substance. A review found a faster choice reaction time after a single dose than under placebo, an agent without an active ingredient 1. Individual studies showed faster reactions to simple stimuli 26 and in the Stroop test 24. Another review found no difference there 4.

Stress and Tension

In schizophrenia, L-theanine as an add-on to medication treatment reduced anxiety more than placebo 17. A review considers a reduction in stress under load possible 8. A review found only a slight reduction in acute stress, especially in less careful studies 1.

Sleep and Sleep Quality

Boys with ADHD slept for a larger part of the night with L-theanine than with placebo, but did not fall asleep faster 14. Healthy adults reported falling asleep faster and sleeping less often disturbed with L-theanine than with placebo 21. In anxiety disorder, sleep satisfaction increased more than under placebo 19. A review overall assesses the studies as an indication of better sleep 3.

Mood and Relaxation

As an add-on to the antidepressant sertraline, L-theanine in depression improved symptoms more than placebo 15. A review found fewer depressive symptoms after a single dose in healthy individuals than under placebo 1. A controlled study (with a comparison group) found less tension after a mental task than under placebo 28. The findings come predominantly from small, short studies.

Theanine Combined with Caffeine

In two small studies, the combination of L-theanine and caffeine accelerated the reaction to target stimuli 2327. L-theanine alone, however, had the same effect 2327. Those who received L-theanine together with caffeine were less tense in a stress situation than someone who received only caffeine 18. Another study found no difference of the combination compared with placebo, because the effects of both substances canceled each other out 25.

Blood Pressure and Cardiovascular Function

For blood pressure and cardiovascular health, the evidence is limited. A controlled study found after a cognitive task a lower blood pressure increase, but only in strongly reacting individuals 28. A randomized (participants assigned by lot) controlled study found no difference in blood pressure, heart rate and heart rate variability 22. Both studies were very small and short.

Other Investigations

As an add-on to medications against psychoses, L-theanine in schizophrenia improved individual symptoms more than placebo 1617. A secondary analysis found a statistical association between the improvement and two blood values 20. The findings come from small, short add-on studies. Since both groups received the antipsychotics, the difference is attributable to L-theanine.

4. How Was L-Theanine Taken in the Studies?

In the studies, L-theanine was predominantly given as the pure substance. It was used in capsules, powders or chewable tablets. Sometimes it was contained in foods such as sorbet. In addition, theanine-containing beverages such as matcha and extracts were tested. Individual investigations gave L-theanine in addition to ongoing medication treatment.

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

In the studies, L-theanine was predominantly well tolerated. Serious adverse events were not reported 117. As an add-on to antipsychotics or sertraline, side effects did not differ from placebo 151617. Many studies tested only single doses over short periods. Larger and longer placebo studies on sleep and anxiety are still pending.

All details with tables and sources: full expert page on L-Theanine