L-theanine
Sleep
Amino acid from tea, studied for taking the edge off stimulants without sedating you.
What the evidence says
Several small-to-mid human trials for acute stress and attention, often paired with caffeine. Long-term data is thin.
What studies used
100–400 mg. With caffeine, or in the evening.
Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.
Evidence base
established literature
Strong human evidence: either a phase 3 or 4 trial report alongside review-level evidence, or ten or more randomised controlled trial reports.
This letter measures how much human research exists, not whether it works for you — the tier above (Moderate) is the read on quality.
Research (12)
- The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic ReviewCureus · 2021
- Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled TrialNutrients · 2019
- L-theanine, a natural constituent in tea, and its effect on mental stateAsia Pac J Clin Nutr · 2008
- The combined effects of L-theanine and caffeine on cognitive performance and moodNutr Neurosci · 2008
- L-Theanine and Immunity: A ReviewMolecules · 2023
- L-Theanine reduces psychological and physiological stress responsesBiol Psychol · 2007
- The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic ReviewPlant Foods Hum Nutr · 2020
- GABA and l-theanine mixture decreases sleep latency and improves NREM sleepPharm Biol · 2019
- The effects of L-theanine, caffeine and their combination on cognition and moodBiol Psychol · 2008
- l-theanine: From tea leaf to trending supplement - does the science match the hype for brain health and relaxation?Nutr Res · 2025
- Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled StudyJ Med Food · 2021
- The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysisSleep Med Rev · 2025
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