L-theanine → Cognitive performance
Higher L-theanine moves Cognitive performance only in some conditions. Read the mechanism.
Kahathuduwa 2018 found that 200 mg of L-theanine alone sped recognition visual reaction time versus placebo in 20 healthy men. Dassanayake 2023 saw a similar simple-reaction win in 32 young adults and no win on harder attention tasks. Tea-dose theanine alone has often missed.
Randomized trial · Contested · N=32
Supported by an experiment or a tightly identified design. Read the caveats.
Mechanism
Authors treat L-theanine as a quiet attention amino acid. Many files also assign caffeine. Kahathuduwa, Dassanayake, Amarakoon and Weerasinghe crossed 20 men through 200 mg theanine, 160 mg caffeine, both, tea, and water. Theanine alone improved recognition reaction time (P=0.019). The combination was larger. Dassanayake, Kahathuduwa and Weerasinghe crossed 32 young adults through 100, 200, and 400 mg and water. After placebo adjustment, only simple reaction time moved at 100 and 200 mg. Sustained attention and stop-signal did not. Dodd, Kennedy, Riby and Haskell-Ramsay crossed 24 people through 50 mg theanine, 75 mg caffeine, both, and placebo. Theanine alone did not change behavior. The combination erased caffeine's attention and mood effects. Haskell, Kennedy, Milne, Wesnes and Scholey found that 250 mg theanine alone raised headache ratings and lowered serial-seven accuracy. Caffeine and the combination helped other tasks. Giesbrecht 2011 (n=44) and Einother 2010 found that 97 mg theanine plus 40 mg caffeine improved switch-task accuracy versus placebo.
Caveats
Researchers assigned people to a dose or a control, so this is a trial stamp. Theanine alone and theanine-plus-caffeine are not the same drink. More papers of the same design do not settle the claim. High-dose theanine can move a simple reaction task. Tea-ratio theanine alone has often been null. Haskell's 250 mg arm moved serial sevens the wrong way. This is a journal entry, not medical advice and not a reason to take theanine for focus.
Effect
qualitative. Kahathuduwa 2018: 200 mg alone, N=20, RVRT P=0.019. Dassanayake 2023: N=32, simple RT only. Dodd 2016: 50 mg alone null. Haskell 2008: 250 mg alone serial sevens down. Combo files move attention.
Nodes
Named confounders
Cite this page
What Causes What. “L-theanine → Cognitive performance.” https://whatcauseswhat.org/edges/e-theanine-cognition (atlas updated 2026-09-02).
Papers
- Acute effects of theanine, caffeine and theanine-caffeine combination on attention.
CN Kahathuduwa, TL Dassanayake, AMT Amarakoon, VS Weerasinghe · 2018 · Nutritional neuroscience
- Dose-response effect of L-theanine on psychomotor speed, sustained attention, and inhibitory control: a double-blind, placebo-controlled, crossover study.
TL Dassanayake, D Wijesundara, CN Kahathuduwa, VS Weerasinghe · 2023 · Nutritional neuroscience
- 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.
FL Dodd, DO Kennedy, LM Riby, CF Haskell-Ramsay · 2016 · Psychopharmacology
- The effects of L-theanine, caffeine and their combination on cognition and mood.
CF Haskell, DO Kennedy, AL Milne, KA Wesnes, AB Scholey · 2008 · Biological psychology
- The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.
T Giesbrecht, JA Rycroft, MJ Rowson, EA De Bruin · 2011 · Nutritional neuroscience
- L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness.
SJ Einöther, VE Martens, JA Rycroft, EA De Bruin · 2010 · Appetite