L-theanine
An amino acid from tea leaves, taken alone or with caffeine for calm focus and stress.
Focus Anxiety Sleep
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Research
REALITY CHECK // A 2026 meta-analysis of 31 RCTs found that a single 200 mg dose modestly improved attention in healthy adults.
Levels: how we grade evidence. Grey = evidence of no benefit; amber = evidence it makes this goal worse.
Ratings are self-reported by a self-selected group of users: how it felt, not proof that it works.
>_ Protocol data coming soon: label checker ("Check your bottle"), study snapshot and form comparison for L-theanine.
How it was studied
Summary
A 2026 meta-analysis of 31 RCTs found that a single 200 mg dose modestly improved attention in healthy adults. Effects on acute stress were small and driven by higher-risk studies. In GAD it did not beat placebo. Many studies test it together with caffeine, which makes the effect of theanine alone harder to separate. Sleep data come from one trial in boys with ADHD; in adults with anxiety, theanine did not improve insomnia scores. The same meta-analysis found no effect on fatigue.
Mechanism
Crosses into the brain and is thought to modulate glutamate and GABA signalling. It relaxes without sedating. With caffeine, it appears to soften jitteriness.
Typical studied dose
Single doses of 200 mg taken 30–60 minutes before tasks are typical. Stress studies used 200–400 mg/day. The cited caffeine-combination trials used 97 mg theanine with 40 mg caffeine, and 250 mg theanine with 150 mg caffeine. One sleep trial in boys with ADHD used 400 mg/day under clinical supervision.
Upper limit
No upper limit has been set by EFSA or US IOM/NIH. Trials of up to 900 mg/day for 8 weeks reported no serious adverse events. A commercial L-theanine ingredient holds FDA GRAS status.
Popular stacks with L-theanine
Not enough stack data yet. A combination with L-theanine appears here once 5 people rate the same set.
Red flags: interactions and who should avoid it
Interactions
May add to blood-pressure-lowering drugs (small studies show reduced blood pressure reactivity under stress). It may add to the calming effect of sedatives. Use with psychiatric medication only under a specialist's supervision. Caffeine is a common, intended pairing. Taken alone, one trial reported more headache ratings.
Avoid or ask a doctor first if
Pregnancy or breastfeeding (no safety data). Children, except under clinical supervision. Low blood pressure. Psychiatric conditions on medication, unless a specialist agrees. Choose pure L-theanine: DL-theanine is half the inactive D form.
Sources (PubMed)
- Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.
PMID 42410082 · 2026 · meta-analysis of RCTs200 mg improves attention; stress effect modest; no fatigue effect.
- The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.
PMID 21040626 · 2010 · RCT97 mg theanine + 40 mg caffeine improved task switching, alertness.
- The effects of L-theanine, caffeine and their combination on cognition and mood.
PMID 18006208 · 2007 · RCTCombination beat caffeine alone; theanine alone raised headache ratings.
- The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.
PMID 31758301 · 2020 · systematic review of RCTs200–400 mg/day may reduce stress in people under stressful conditions.
- L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial.
PMID 30580081 · 2018 · RCT (double-blind, placebo-controlled)Added to antidepressants in GAD: no anxiety benefit over placebo.
- The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial.
PMID 22214254 · 2011 · RCT (double-blind, placebo-controlled)400 mg/day improved actigraphy sleep efficiency in boys with ADHD.
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