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L-Theanine: What It Is, Evidence and Safety

VITAMINS & SUPPLEMENTS · GUIDE

L-Theanine for Sleep, Stress and Anxiety: What Trials Found

What randomized trials and reviews found for L-theanine and sleep, stress and anxiety, by outcome, with the limits of small, short studies and when to see a clinician.

Content last updated . This page has not been medically reviewed.

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Quick answer
L-theanine is an amino acid found mainly in tea. Small trials and reviews suggest it may modestly help some people who are under stress or have trouble sleeping, but the studies are small, short, and in some cases supported by companies that supplied the product, and results differ by outcome. A 2025 meta-analysis of 19 sleep trials found small gains in self-rated sleep, and the authors said studies of "pure" L-theanine are lacking. [1] It is not a treatment for an anxiety disorder or insomnia, and no study here shows it replaces care from a clinician.

How the evidence is labeled

Promising but limited: small trials point the same way but are not enough to be sure. Mixed: results disagree or depend on the outcome. Insufficient evidence: too few good studies. Biomarker: a lab or brain-wave measure, such as cortisol, which is not the same as feeling better. Amounts below are study amounts, not advice.

What trials found, by outcome

9 findings · 4 supported · 3 mixed · 2 limited or unclearThe colour follows the evidence label on each card.

  1. Stress and anxiety in people under stress

    Promising but limited

    A systematic review of 9 randomized trials of L-theanine supplements versus a control suggested 200-400 mg a day (the amounts in those trials) may assist in people exposed to stressful conditions, and called for longer and larger studies. [2]

  2. Stress symptoms in healthy adults, 4 weeks

    Promising but limited (small, industry link)

    In 30 healthy adults in a crossover trial, scores on depression, trait anxiety and sleep-quality questionnaires decreased after L-theanine compared with placebo. [3] Two authors worked for the company that supplied the tablets. [3]

  3. Acute stress, single dose

    Biomarker only

    In a trial using a mental arithmetic stress test, L-theanine was followed by greater drops in salivary cortisol one hour later than placebo. [4]

  4. Perceived stress over 28 days

    Mixed

    In 30 adults with moderate stress, perceived-stress scores fell in the L-theanine group, but placebo scores fell by almost the same amount (17.88 percent against 17.98 percent), and there was no group difference in salivary cortisol. [5]

  5. Sleep (all ages)

    Promising but limited, mostly self-rated

    A meta-analysis of 19 randomized trials (897 people) found small improvements in self-rated sleep onset time, daytime dysfunction and overall sleep quality. [1]

  6. Sleep, tea-based

    Mixed

    A trial of daily matcha found no differences from the control group in EEG-measured total sleep time, sleep latency or time awake after sleep onset. [6] A 12-month trial in older adults with cognitive decline found only a trend in sleep quality that was not statistically significant. [7]

  7. Sleep, multi-ingredient blend

    Insufficient evidence for L-theanine itself

    A small crossover study (16 participants) of a blend of tryptophan, glycine, magnesium, tart cherry powder and L-theanine cannot show which ingredient did what. [8]

  8. Mood, sleep and thinking in healthy people

    Mixed

    A meta-analysis of 50 trials of tea, theanine, or theanine with caffeine found small differences on some tests, with wide uncertainty about size and direction. [9]

  9. People with diagnosed conditions

    Promising but limited

    A review of 11 randomized trials found L-theanine reduced psychiatric symptoms more than control conditions in people with schizophrenia, anxiety disorders and ADHD, and said more studies were needed to confirm this. [10]

Why the results are hard to read

  • Small and short. The trials above followed tens of people for days to weeks. The 28-day trial had 15 people per group. [5] The stress review asked for longer and larger studies. [2]
  • Placebo effect. In the 28-day trial the placebo group improved almost as much as the L-theanine group on perceived stress. [5]
  • Different products. Studies used supplements, tea, matcha and blends, and a tea meta-analysis said more research is needed with tea-equivalent amounts in everyday life. [9] Do not assume one form's result applies to another.
  • Funding. Some authors work for companies that supplied the product or tea. [3][9][6]
  • Other groups. Findings in healthy adults do not transfer to children, older adults or people with diagnosed conditions.

Where to go next

For goals rather than ingredients, see Better Sleep, Stress and Relaxation and Natural Sleep Aids Compared. For the ingredient overview see L-Theanine: What It Is, Evidence and Safety, and for comparisons see Calming Supplements Compared. Attention questions are on L-Theanine for Attention and ADHD.

Frequently asked questions

Does L-theanine help you sleep?

A meta-analysis found small improvements in self-rated sleep onset and sleep quality, but one tea-based trial found no change in measured sleep. [1][6] The evidence is promising but limited.

Does L-theanine reduce anxiety?

A systematic review suggested it may help people under stressful conditions, and called for larger, longer studies. [2] A separate review reported benefits in people with anxiety disorders but said confirmation is needed. [10] It is not a substitute for assessment and care.

Does L-theanine lower stress hormones?

One single-dose trial reported lower salivary cortisol after a stress test, [4] but a 28-day trial found no group difference in cortisol. [5] Cortisol change is a biomarker, not proof you will feel better.

Is the amount in tea the same as in supplements?

Not necessarily. A matcha trial reported 50.3 mg of theanine in its daily amount, [6] while the stress review discussed supplement amounts of 200-400 mg a day. [2] See L-Theanine in Tea and in Supplements.

Who should ask a professional first?

Anyone on prescribed medicines, pregnant or breastfeeding, giving a supplement to a child, or with ongoing sleep or anxiety problems. [11][12]

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Safety in brief
Trials reported few problems, but they were small and short. See L-Theanine Side Effects, Interactions and Who Should Ask First. Tea also contains caffeine, which can disturb sleep. See Caffeine, Alcohol, Nicotine and Sleep.
When to see a clinician
  • Sleep. The NHS advises seeing a GP if changing your sleeping habits has not helped, if you have had trouble sleeping for months, or if it affects daily life, and says to check with your doctor before taking anything for sleep problems. [11]
  • Anxiety. The NHS advises seeing a GP if you think you might have generalised anxiety disorder or if treatment is not helping. [12]
  • Crisis. In the US, if you or someone you know is struggling or having thoughts of suicide, call or text 988; in a life-threatening situation, call 911. [13]
  • Medicines and pregnancy. Ask a pharmacist or clinician before adding any supplement if you take prescribed medicines, are pregnant or breastfeeding, or are giving it to a child.
References
  1. Bulman A et al., The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev 2025. Read 2026-10-23.
  2. Williams JL et al., The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review. Plant Foods Hum Nutr 2020. Read 2026-10-23.
  3. Hidese S et al., Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients 2019. Read 2026-10-23.
  4. Evans M et al., A randomized, triple-blind, placebo-controlled, crossover study to investigate the efficacy of a single dose of L-theanine on stress in a healthy adult population. Neurol Ther 2021. Read 2026-10-23.
  5. Moulin M et al., Safety and efficacy of L-theanine supplementation for 28 days in healthy adults with moderate stress: a randomized, double-blind, placebo-controlled trial. Neurol Ther 2024. Read 2026-10-23.
  6. Baba Y et al., Matcha does not affect electroencephalography during sleep but may enhance mental well-being: a randomized placebo-controlled clinical trial. Nutrients 2024. Read 2026-10-23.
  7. Uchida K et al., Effect of matcha green tea on cognitive functions and sleep quality in older adults with cognitive decline: a randomized controlled study over 12 months. PLoS One 2024. Read 2026-10-23.
  8. Langan-Evans C et al., Nutritional modulation of sleep latency, duration, and efficiency: a randomized, repeated-measures, double-blind deception study. Med Sci Sports Exerc 2023. Read 2026-10-23.
  9. Payne ER et al., Effects of tea or its bioactive compounds l-theanine or l-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev 2025. Read 2026-10-23.
  10. Moshfeghinia R et al., The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review. BMC Psychiatry 2024. Read 2026-10-23.
  11. NHS (UK), Insomnia (page last reviewed 19 March 2024) Read 2026-10-23.
  12. NHS (UK), Generalised anxiety disorder in adults (page last reviewed 22 October 2024) Read 2026-10-23.
  13. National Institute of Mental Health (US), Anxiety Disorders Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.