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L-Theanine

Camellia sinensis
Evidence Level
Strong
8 Clinical Trials
8 Documented Benefits
4/5 Evidence Score

L-Theanine, an amino acid primarily found in green tea (Camellia sinensis), is commonly supplemented in doses of 100–400 mg/day to promote relaxation and cognitive health. It enhances alpha brain wave activity, inducing a calm, focused mental state without sedation, making it effective for reducing stress and anxiety. L-Theanine may improve sleep quality by promoting relaxation and reducing caffeine-induced overstimulation when combined with caffeine, enhancing attention and cognitive performance. It also exhibits neuroprotective properties by modulating neurotransmitters like GABA, serotonin, and dopamine, potentially supporting mood and reducing symptoms of mild depression. Additionally, L-Theanine has mild antioxidant effects, protecting cells from oxidative stress. Side effects are rare but may include mild headaches or drowsiness at high doses. Consult a healthcare provider for appropriate dosing, especially if on medications like antidepressants or stimulants, to avoid potential interactions.

Studied Dose 100–400 mg/day; relaxation: 200 mg; caffeine synergy: 100–200 mg with caffeine; sleep: 200–400 mg before bed
Active Compound L-Theanine (free amino acid)

Benefits

Promotes Relaxation Without Sedation

L-Theanine, an amino acid found in green tea, increases alpha brain wave activity, promoting a calm, alert state without causing drowsiness.

Supported by Trial 1, Trial 2

Reduces Stress and Anxiety

By modulating neurotransmitters like GABA and serotonin, L-Theanine may reduce stress and anxiety symptoms, helping to calm the mind.

Supported by Trial 1, Trial 2

Improves Focus and Attention

L-Theanine, often paired with caffeine, enhances cognitive performance by improving focus and attention while reducing jitteriness.

Supported by Trial 2, Trial 6

Enhances Sleep Quality

L-Theanine may improve sleep by promoting relaxation and reducing anxiety, helping with faster sleep onset and better rest.

Supported by Trial 1, Trial 3

Supports Cognitive Function

By protecting neurons from oxidative stress and modulating glutamate, L-Theanine may support memory and cognitive health, though evidence is preliminary.

Supported by Trial 6, Trial 2

Mood Improvement

L-Theanine may elevate mood by increasing serotonin and dopamine levels, potentially alleviating mild depressive symptoms.

Supported by Trial 2, Trial 7

Cardiovascular Health Support

L-Theanine may lower blood pressure and heart rate during stress, contributing to cardiovascular health, though data is limited.

Supported by Trial 1, Trial 2

Immune System Modulation

L-Theanine may enhance immune function by supporting anti-inflammatory responses and increasing glutathione levels, but more research is needed.

Supported by Trial 2, Trial 6

Mechanism of action

1

Promotes Alpha Brain Wave Activity

L-Theanine crosses the blood-brain barrier and increases alpha brain wave activity, inducing a relaxed yet alert mental state without sedation.

2

Modulates Neurotransmitters

It enhances levels of GABA, serotonin, and dopamine by inhibiting excitatory neurotransmitters like glutamate, promoting relaxation and reducing stress.

3

Reduces Glutamate Excitotoxicity

L-Theanine binds to glutamate receptors, reducing excitotoxicity and protecting neurons from damage, which may support cognitive health.

4

Synergizes with Caffeine

When combined with caffeine, L-Theanine enhances dopamine release and modulates adenosine receptors, improving focus and attention while reducing jitteriness.

5

Lowers Stress Response

L-Theanine inhibits cortisol release and reduces sympathetic nervous system activity, lowering heart rate and blood pressure during stress.

6

Improves Sleep Regulation

By increasing GABA and reducing excitatory signaling, L-Theanine promotes relaxation, facilitating faster sleep onset and better sleep quality.

7

Antioxidant Effects

L-Theanine may increase glutathione levels, reducing oxidative stress and supporting neuronal and immune health, though mechanisms are not fully elucidated.

8

Anti-Inflammatory Effects

L-Theanine modulates cytokine production, potentially reducing inflammation, which may contribute to its immune and cardiovascular benefits.

Clinical trials

1
L-Theanine for Generalized Anxiety Disorder — Adjunctive Clinical Trial

Randomized controlled trial in 46 patients with generalized anxiety disorder (GAD) randomized to L-theanine (450-900 mg/day) vs placebo as adjunct to standard care for 8 weeks. Outcomes: HAM-A, sleep, insomnia. (J Psychiatr Res)

46 GAD patients. 8-week intervention.

Primary endpoint negative: L-theanine did not significantly improve HAM-A anxiety scores vs placebo. Modest improvements in sleep variables. Important honest finding — L-theanine has not held up in rigorous clinical anxiety populations as marketing might suggest. Effects in healthy individuals under acute stress are more replicable than in clinical anxiety disorders.

2
L-Theanine for Stress and Cognition in Healthy Japanese Adults — Crossover Clinical Trial

Double-blind, placebo-controlled crossover trial in 30 healthy Japanese adults receiving L-theanine (200 mg) vs placebo. Outcomes: stress-related symptoms, cognitive performance. (Nutrients)

30 healthy Japanese adults. Crossover.

L-theanine modestly reduced stress-related symptoms and improved verbal fluency and executive function tests vs placebo. Effects in healthy adults are real but modest. Generally well-tolerated.

3
Suntheanine® for Sleep in Boys with ADHD — Clinical Trial

Randomized controlled trial of L-theanine (Suntheanine®, 400 mg/day) vs placebo in 98 boys aged 8-12 with ADHD for 6 weeks. Outcomes: actigraphy-measured sleep efficiency, sleep latency. (Altern Med Rev)

98 boys with ADHD. 6-week intervention.

L-theanine modestly improved objective sleep efficiency (~92.4% vs 91.1% placebo) — small effect. Generally well-tolerated. Note: ADHD treatment requires comprehensive evaluation; L-theanine does not replace standard ADHD therapy. Modest sleep effect in this specific pediatric population.

4
AlphaWave® L-Theanine Acute Stress — Crossover Clinical Trial

Crossover clinical trial in 16 healthy adults with moderate stress receiving single dose of AlphaWave® L-theanine vs placebo. Outcomes: acute stress response (Trier social stress test or similar). (2021)

16 healthy adults under acute stress.

AlphaWave® modestly reduced subjective stress and physiological stress markers vs placebo. Small acute crossover trial; effect sizes modest. Industry-funded.

5
AlphaWave® L-Theanine 28-Day Safety/Efficacy — Clinical Trial

Randomized controlled trial of AlphaWave® L-theanine (400 mg/day) vs placebo in 30 healthy adults with moderate stress for 28 days. (2024)

30 moderately stressed adults. 28-day intervention.

AlphaWave® modestly improved subjective stress measures. Generally safe. Small trial, industry-funded. Modest effects consistent with broader L-theanine literature.

6
L-Theanine for Cognitive Function in Older Japanese Adults — Clinical Trial

Double-blind clinical trial in 30 Japanese adults aged 50-69 receiving L-theanine (200 mg/day) vs placebo for 12 weeks. Outcomes: cognitive function tests. (2021)

30 older adults aged 50-69.

Modest improvements in attention and memory tasks vs placebo. Small trial; emerging evidence for cognitive applications in older adults.

7
L-Theanine for Schizophrenia — Adjunctive Clinical Trial

Randomized controlled trial in 60 patients with schizophrenia or schizoaffective disorder receiving L-theanine (400 mg/day) vs placebo as adjunct to antipsychotics for 8 weeks. Outcomes: PANSS scales, anxiety. (J Clin Psychiatry)

60 schizophrenia/schizoaffective patients.

L-theanine modestly improved positive symptoms, activation factors, and anxiety vs placebo. Note: niche psychiatric application; should not replace established antipsychotic therapy; adjunctive role under psychiatric supervision only.

8
L-Theanine Adjunct to Sertraline for MDD — Clinical Trial

Clinical trial assessing L-theanine (250 mg/day) vs placebo as adjunct to sertraline in 46 patients with major depressive disorder for 8 weeks. (2023)

46 MDD patients on sertraline.

L-theanine + sertraline showed modest improvements in some depression measures vs sertraline + placebo. Small trial; emerging adjunctive evidence. Should not replace standard depression therapy.

Side effects and drug interactions

Common Potential side effects

Drowsiness or Sedation: L-Theanine may cause mild drowsiness, especially at higher doses or when combined with other calming agents, though it typically promotes relaxation without sedation.
Headache: Some users report headaches, possibly due to L-Theanine’s effects on neurotransmitter activity or individual sensitivity.
Gastrointestinal Discomfort: Mild nausea, stomach upset, or diarrhea may occur, particularly with high doses or in sensitive individuals.
Dizziness or Lightheadedness: L-Theanine may cause dizziness, potentially linked to its blood pressure-lowering effects or neurotransmitter modulation.
Mood Changes: Rare cases of irritability or anxiety may occur, possibly due to altered serotonin or dopamine levels in sensitive individuals.
Low Blood Pressure: L-Theanine’s calming effects may lower blood pressure, causing hypotension, especially in those on antihypertensive medications.
Allergic Reactions: Rare allergic responses, such as rash or itching, may occur, typically related to supplement additives or L-Theanine source materials.

Important Drug interactions

Drug Interactions: L-Theanine may enhance the effects of sedatives, antidepressants, or stimulants (e.g., caffeine), potentially altering their efficacy or causing side effects.

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Frequently asked questions about L-Theanine

How much L-theanine should I take?

Common doses are 100 to 200 mg, taken once or up to twice daily. For pairing with caffeine, a roughly 2-to-1 ratio of L-theanine to caffeine (for example 200 mg theanine with 100 mg caffeine) is popular for smooth focus.

Does L-theanine make you sleepy?

L-theanine promotes a calm, relaxed-but-alert state rather than sedation, so most people do not feel drowsy during the day. Taken at night it can support relaxation and help with falling asleep, without the grogginess of a sleep aid.

Can I take L-theanine with coffee?

Yes, and it is a popular combination. L-theanine takes the edge off caffeine's jitteriness and can smooth out focus, which is why the two are often stacked. Many people find the pairing gives calmer, more sustained energy than coffee alone.

Is L-theanine safe to take daily?

L-theanine has an excellent safety profile and occurs naturally in tea. It is generally well tolerated for daily use with few side effects. If you are pregnant, breastfeeding, or on blood-pressure medication, check with your doctor.

What is L-Theanine?

L-Theanine, an amino acid primarily found in green tea (Camellia sinensis), is commonly supplemented in doses of 100–400 mg/day to promote relaxation and cognitive health. It enhances alpha brain wave activity, inducing a calm, focused mental state without sedation, making it effective for reducing stress and anxiety.

What is L-Theanine used for?

L-Theanine is researched primarily for Cognitive, Sleep Health, and Stress & Anxiety. L-Theanine, an amino acid found in green tea, increases alpha brain wave activity, promoting a calm, alert state without causing drowsiness.

What is the recommended dosage of L-Theanine?

The clinically studied dose is 100–400 mg/day; relaxation: 200 mg; caffeine synergy: 100–200 mg with caffeine; sleep: 200–400 mg before bed Always follow the product label and check with a healthcare provider for personal advice.

Is L-Theanine safe, and does it have side effects?

For most healthy adults, L-Theanine is well tolerated at studied doses. Reported effects can include: Drowsiness or Sedation: L-Theanine may cause mild drowsiness, especially at higher doses or when combined with other calming agents, though it typically promotes relaxation without sedation. It may also interact with some medications. L-Theanine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does L-Theanine interact with any medications?

Possible interactions include: Drug Interactions: L-Theanine may enhance the effects of sedatives, antidepressants, or stimulants (e.g., caffeine), potentially altering their efficacy or causing side effects. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for L-Theanine?

NutraSmarts rates the evidence for L-Theanine as Strong (4 out of 5). It is backed by 8 clinical trials and 8 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(8 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Sarris J, Byrne GJ, Cribb L, Oliver G, Murphy J, Macdonald P, Nazareth S, Karamacoska D, Galea S, Short A, Ee C, Birling Y, Menon R, Ng CH. L-theanine in the adjunctive treatment of generalized anxiety disorder: a double-blind, randomised, placebo-controlled trial. J Psychiatr Res. 2019;110:31-37. doi: 10.1016/j.jpsychires.2018.12.014.PubMedUsed to support: Generalized anxiety disorder RCT — 46 patients with GAD; L-theanine 450-900 mg/day as adjunct to standard treatment did not significantly outperform placebo on anxiety scales over 10 weeks, though sleep satisfaction improved
  2. Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients. 2019;11(10):2362. doi: 10.3390/nu11102362.PubMedUsed to support: Stress and cognition crossover RCT — 30 Japanese adults; L-theanine 200 mg/day for 4 weeks reduced stress-related symptoms (depression, anxiety, sleep disturbance) and improved verbal fluency and executive function vs placebo
  3. Lyon MR, Kapoor MP, Juneja LR. 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. Altern Med Rev. 2011;16(4):348-54.PubMedUsed to support: ADHD sleep RCT — 98 boys aged 8-12 with ADHD; Suntheanine L-theanine 400 mg/day for 6 weeks significantly improved sleep efficiency and reduced nocturnal activity vs placebo as measured by actigraphy
  4. Evans M, McDonald AC, Xiong L, Crowley DC, Guthrie N. A randomized, triple-blind, placebo-controlled, crossover study to investigate the efficacy of a single dose of AlphaWave® L-theanine on stress in a healthy adult population. Neurol Ther. 2021;10(2):1061-1078. doi: 10.1007/s40120-021-00284-x.PubMedUsed to support: Acute stress crossover RCT — 16 healthy adults; a single 200 mg dose of AlphaWave L-theanine reduced subjective stress and salivary cortisol response to an acute stressor vs placebo
  5. Moulin M, Crowley DC, Lewis ED, Stainton J, Xiong L, Guthrie N, Evans M. A randomized, double-blind, placebo-controlled trial to evaluate the effects of a 28-day intervention with AlphaWave® L-theanine on stress-related parameters in healthy adults. Neurol Ther. 2024;13(4):1135-1153. doi: 10.1007/s40120-024-00637-2.PubMedUsed to support: 28-day stress RCT — 30 healthy adults; AlphaWave L-theanine 200 mg/day reduced perceived stress and improved sleep quality and emotional state over 28 days vs placebo
  6. Baba Y, Inagaki S, Nakagawa S, Kaneko T, Kobayashi M, Takihara T. Effects of l-theanine on cognitive function in middle-aged and older subjects: a randomized placebo-controlled study. J Med Food. 2021;24(4):333-341. doi: 10.1089/jmf.2020.4803.PubMedUsed to support: Older adult cognition RCT — Japanese adults aged 50-69; L-theanine 100.6 mg/day for 12 weeks improved verbal fluency and executive function vs placebo, with greatest benefit in those with lower baseline scores
  7. Ritsner MS, Miodownik C, Ratner Y, Shleifer T, Mar M, Pintov L, Lerner V. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. J Clin Psychiatry. 2011;72(1):34-42. doi: 10.4088/JCP.09m05324gre.PubMedUsed to support: Schizophrenia adjunct RCT — 60 patients with schizophrenia or schizoaffective disorder; L-theanine 400 mg/day added to standard antipsychotics for 8 weeks reduced positive symptoms, activation, and anxiety vs placebo
  8. Shamabadi A, Hasanzadeh A, Ahmadzade A, Ghadimi H, Gholami M, Akhondzadeh S. An 8-week, randomized, double-blind, placebo-controlled clinical trial assessing the efficacy and safety of L-theanine adjunct to sertraline for major depressive disorder. J Affect Disord. 2023;333:38-43. doi: 10.1016/j.jad.2023.04.029.PubMedUsed to support: Major depression adjunct RCT — 60 patients with MDD; L-theanine 200 mg/day combined with sertraline for 8 weeks produced significantly greater reductions in HAM-D scores than sertraline plus placebo