MVIIIHealth The MVIII app
← Back

Research · Supplements

L-Theanine

Across 31 trials, a single 200 mg dose sped choice reaction time, and the drop in acute stress was modest and driven by high-risk studies. Pooled sleep trials found small gains in self-rated sleep, mostly with mixed products. An 8-week trial in generalized anxiety disorder found no difference from placebo. No serious adverse events were reported.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Found naturally in tea.
Also called
theanine, L-theanine, gamma-glutamylethylamide, green tea amino acid, Suntheanine, AlphaWave
Taken for
stress, anxiety, sleep, focus, attention, calm, pairing with caffeine

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

Reported risks0

No risks sourced yet.

What people take it for, and what was found

Shown to help3

Strong

Attention and reaction time

Shown to improve choice reaction time in the hour after a single 200 mg dose in adults. Simple reaction time and the Stroop test did not change.

The numbers and sources
Effect
Across 31 RCTs (1,168 participants), a single 200 mg dose taken 30 to 60 minutes before testing improved choice reaction time (SMD 0.51, 95% CI 0.25 to 0.77) [1]. A separate meta-analysis of healthy participants found theanine alone improved choice reaction time in the first hour (SMD -0.35, 95% CI -0.61 to -0.10), and theanine plus caffeine improved some attention-task accuracy in the second hour [2]. A third meta-analysis of 5 RCTs (148 healthy adults) found faster rapid visual information processing and recognition reaction time (MD -15.20 ms, 95% CI -28.99 to -1.41), and no difference in simple reaction time or the Stroop test [3].
Population
Healthy and clinical populations [1]. Healthy participants only [2][3].
Sources
[1], [2], [3]
Caveats
The second review notes the confidence intervals often left the direction and size of effects uncertain [2]. The third pooled only 5 trials of varied products, and simple reaction time and Stroop results did not differ [3]. The reviews agree on choice and recognition reaction time, not on every attention test. Many trials pair theanine with caffeine.
Moderate

Sleep

Shown to improve self-rated sleep onset, daytime function and sleep quality modestly in people of all ages.

The numbers and sources
Effect
In 18 RCTs pooled (897 participants across 19 articles), theanine improved self-rated sleep onset latency (SMD 0.15, 95% CI 0.01 to 0.29), daytime dysfunction (SMD 0.33, 95% CI 0.16 to 0.49) and overall sleep quality score (SMD 0.43, 95% CI 0.04 to 0.83) [6]. In a 4-week crossover trial of 200 mg a day in 30 adults, PSQI scores for sleep latency, sleep disturbance and use of sleep medication fell compared with placebo [7].
Population
People of all ages and health status [6]. 30 adults without major psychiatric illness [7].
Sources
[6], [7]
Caveats
The review authors note a lack of studies on pure theanine [6]. The crossover trial was funded by Taiyo Kagaku, which supplied the theanine, and two authors were its employees [7].
Limited

Symptoms of mental disorders

Limited evidence: a review of 11 trials reported fewer symptoms in schizophrenia, anxiety disorders and ADHD, often alongside medication. One anxiety trial found no effect.

The numbers and sources
Effect
A systematic review of 11 RCTs from six countries reported that theanine reduced psychiatric symptoms more than control in schizophrenia, anxiety disorders and ADHD [8].
Population
Patients with schizophrenia, ADHD, OCD, major depression, sleep disorders, GAD or Tourette syndrome, often taking it alongside their medication [8].
Sources
[8]
Caveats
No pooled effect sizes are given in the abstract. Results differ by disorder, and an adjunctive GAD trial found no anxiety effect [9].

Mixed results1

Limited

Stress and anxiety

Limited evidence: acute stress fell modestly, mostly in high-bias studies, and a 28-day trial found perceived stress fell equally on placebo.

The numbers and sources
Effect
The reduction in acute stress after a single dose was modest (SMD 0.31) and largely influenced by high-risk-of-bias studies. Anxiety effects were inconsistent and not significant, except one study in psychotic anxiety at 400 mg a day for 8 weeks (SMD 0.54) [1]. A systematic review of 9 trials of pure theanine described possible stress and anxiety reduction at 200 to 400 mg a day in people under stressful conditions [4]. In 30 adults with moderate stress given 400 mg a day for 28 days, perceived stress fell 17.98% with theanine and 17.88% with placebo, and salivary cortisol did not differ between groups [5].
Population
Healthy adults and clinical groups [1][4]. 30 adults with moderate stress [5].
Sources
[1], [4], [5]
Caveats
The 28-day trial was funded by Ethical Naturals, which sells the extract tested, and one author was its employee [5].

Doses studied

Single-dose trials mostly used 200 mg taken 30 to 60 minutes before testing [1]. Repeated-dose trials used 200 to 400 mg a day for 4 weeks to 8 weeks [4][5][7]. The GAD trial used 450 to 900 mg a day alongside antidepressants for 8 weeks [9].

Risks

Checked, no increase found1

Moderate

Adverse events in trials

No serious adverse events were reported across 31 trials lasting up to 8 weeks.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
No serious adverse events were reported across 31 RCTs, and the review compared dropout rates and reasons between theanine and placebo groups [1]. In the 28-day trial, all adverse events resolved by study end or follow-up, and out-of-range laboratory values and vital signs were judged not clinically relevant [5].
Population
1,168 participants in 31 RCTs [1]. 30 adults with moderate stress [5].
Sources
[1], [5]
Caveats
Trials ran from a single dose to 8 weeks. Longer exposure was not measured.

Possible, not studied in people1

UntestedHow often is not known

Drug interactions

Not studied in people. In mice, theanine raised the cancer drug doxorubicin's level in tumors 2.7-fold and lowered it in normal tissues.

No study in people. This rests on animal studies, lab studies.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In mice with ovarian sarcoma, doxorubicin (adriamycin) alone did not slow tumor growth, while theanine plus doxorubicin cut tumor weight to 62% of control. Theanine raised the drug's concentration in the tumor 2.7-fold and lowered it in normal tissues [10]. A review by the same group reported that theanine also enhanced other anthracyclines, cisplatin and irinotecan in mice, and that in tumor cells it blocked drug efflux by inhibiting glutamate transporters [11].
Population
Mice with M5076 ovarian sarcoma, and the same tumor cells in culture [10][11].
Sources
[10], [11]
Caveats
Mouse and cell work from one research group. No study was located that checked theanine alongside chemotherapy or any other drug in people.

Claims tested and not found

  1. That theanine reduces anxiety in generalized anxiety disorder. In 46 people with GAD on stable antidepressants, 450 to 900 mg a day for 8 weeks did not outperform placebo on the HAMA (p = 0.73) or the Insomnia Severity Index (p = 0.35). Self-reported sleep satisfaction was higher with theanine [9].
  2. That theanine lowers cortisol. Salivary cortisol did not differ from placebo after 28 days at 400 mg a day [5].
  3. That theanine reduces fatigue. No effect on fatigue was found across trials [1].

Sources

  1. Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. Molecular Psychiatry. 2026. https://doi.org/10.1038/s41380-026-03727-9
  2. Payne ER, Aceves-Martins M, Dubost J, et al. Effects of Tea (Camellia sinensis) 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. Nutrition Reviews. 2025. https://doi.org/10.1093/nutrit/nuaf054
  3. Mátyus RO, Szikora Z, Bodó D, et al. Promising, but Not Completely Conclusive: The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Trials. Journal of Clinical Medicine. 2025. https://doi.org/10.3390/jcm14217710
  4. Williams JL, Everett JM, D'Cunha NM, 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 for Human Nutrition. 2020. https://doi.org/10.1007/s11130-019-00771-5
  5. Moulin M, Crowley DC, Xiong L, et al. Safety and Efficacy of AlphaWave L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial. Neurology and Therapy. 2024. https://doi.org/10.1007/s40120-024-00624-7
  6. Bulman A, D'Cunha NM, Marx W, et al. The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis. Sleep Medicine Reviews. 2025. https://doi.org/10.1016/j.smrv.2025.102076
  7. Hidese S, Ogawa S, Ota M, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients. 2019. https://doi.org/10.3390/nu11102362
  8. Moshfeghinia R, Sanaei E, Mostafavi S, et al. The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review. BMC Psychiatry. 2024. https://doi.org/10.1186/s12888-024-06285-y
  9. Sarris J, Byrne GJ, Cribb L, et al. L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial. Journal of Psychiatric Research. 2019. https://doi.org/10.1016/j.jpsychires.2018.12.014
  10. Sugiyama T, Sadzuka Y. Enhancing effects of green tea components on the antitumor activity of adriamycin against M5076 ovarian sarcoma. Cancer Letters. 1998. https://doi.org/10.1016/s0304-3835(98)00185-2
  11. Sugiyama T, Sadzuka Y. Theanine and glutamate transporter inhibitors enhance the antitumor efficacy of chemotherapeutic agents. Biochimica et Biophysica Acta. 2003. https://doi.org/10.1016/s0304-419x(03)00031-3

Everything in the library