Theanine
L-theanine is an amino acid from tea studied for relaxation and attention, often alongside caffeine.
Overview
What is L-theanine?
Theanine, or L-theanine, is a non-proteinaceous amino acid found in tea, including green and black tea. L-theanine may reduce stress and anxiety and improve sleep quality; combined with caffeine it may support focus without the sedative effects of L-theanine alone.
Dosage
A typical daily dose of theanine is 100 to 200 mg per day.
In studies, L-theanine is typically used at doses of 100 to 200 mg per day for 2-12 weeks. But doses of up to 400 mg per day have also been safely used for up to 8 weeks.
Effect graph
Effect heatmap
SupplementDEX Database
15 conditions for and rated at least stars. All purchase bands. No minimum star filter.
Database Snapshot
Most theanine research is concentrated in a handful of conditions.
- Stress accounts for 9 of 42 studies (21%).
- Cognitive performance accounts for 7 of 42 studies (17%).
- Sleep accounts for 6 of 42 studies (14%).
- Sparse coverage remains for Anxiety, Attention deficit hyperactivity disorder (ADHD), Age-related cognitive decline.
Dietary Sources
Top dietary sources
Ranked by amount per g
L-theanine is the primary amino acid found in tea and is found in concentrations of around 1–3%. Greater amounts of L-theanine are found in unfermented teas including green tea, matcha or white tea.
- 6.56 mgg
- 6.26 mgg
- 6.09 mgg
- 5.13 mgg
Other sources include Bay Bolete Mushroom.
Safety
L-theanine is well-tolerated at doses of up to 400 mg/day for 8 weeks.
Side effects
- Drowsiness
- Sedation
Special populations
Pregnancy & breastfeeding
AvoidThere is insufficient evidence for the use of L-theanine in pregnant or lactating women. Usage should be avoided in these populations.
Children
Likely safeIn children, L-theanine has been safely used at a dose of 400 mg per day (2 x 200 mg/day) for up to 6 weeks.
Frequently Asked Questions
References
Sources36 references
SupplementDEX uses only high-quality sources to determine supplement effectiveness.
SupplementDEX Database · Anxiety
2 references1.SupplementDEX Database: Anxiety — Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial2019
An RCT of 30 healthy adults found that 200 mg/day L-theanine for 4 weeks significantly reduced trait anxiety, depression, and PSQI sleep scores and improved verbal fluency versus placebo.
2.SupplementDEX Database: Anxiety — The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans2004
An RCT of 16 healthy volunteers found that 200 mg L-theanine showed mild relaxing effects at baseline but neither L-theanine nor 1 mg alprazolam reduced anticipatory anxiety under induced stress.
SupplementDEX Database · Stress
8 references3.SupplementDEX Database: Stress — Safety and Efficacy of AlphaWave® L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial2024
A 28-day randomized double-blind placebo-controlled trial showing that AlphaWave® L-theanine significantly reduced perceived stress and improved mood without adverse effects. A manufacturer-funded study of 30 healthy adults with moderate stress found that L-theanine (400 mg/day) reduced perceived stress by 17.98% after 28 days.
4.SupplementDEX Database: Stress — Effect of Combined Ingestion of L-Theanine and L-Arginine for Short-Term Psychological Stress in Young Adults: A Randomized Placebo-Controlled Study2022
A randomized placebo-controlled study showing that combined L-theanine and L-arginine significantly reduced short-term psychological stress in young adults. A study of 120 healthy young adults undertaking a stress-loading test (Uchida-Kraepelin performance test) given 1) 200 mg L-theanine or 2) 200 mg L-theanine + 50 mg arginine prior to a stressful mental test found that both treatments led to reductions in markers of stress (salivary alpha-amylase activity) 15-min after the test when compared to placebo. The combined treatment trended towards greater reductions in stress as measured by salivary alpha-amylase levels but this was not statistically significant.
5.SupplementDEX Database: Stress — Effect of a Combination of Magnesium, B Vitamins, Rhodiola, and Green Tea (L-Theanine) on Chronically Stressed Healthy Individuals-A Randomized, Placebo-Controlled Study2022
In chronically stressed adults, magnesium-B-vitamin-rhodiola-green tea reduced DASS stress scores versus placebo over 28 days.
6.SupplementDEX Database: Stress — 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 Population2021
A triple-blind crossover study found that a single 200 mg dose of AlphaWave L-theanine increased frontal alpha power and reduced salivary cortisol during acute mental stress versus placebo.
7.SupplementDEX Database: Stress — The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review2020
A meta-analysis of 9 studies (n = 250, Sample size range = 12 to 48) found that 200-400 mg/day L-theanine may reduce stress and anxiety in people exposed to stressful conditions by reducing levels of glutamate and increasing alpha wave activity in the brain. There is not enough evidence from larger, high quality studies suggesting L-theanine reduces stress in people with chronic conditions.
8.SupplementDEX Database: Stress — Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stress2013
An RCT of 20 students found that 400 mg/day L-theanine for 10 days during pharmacy practice significantly reduced subjective stress and salivary α-amylase versus placebo.
9.SupplementDEX Database: Stress — Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses2012
A cross-over study of 14 participants found that L-theanine reduced tension-anxiety compared to placebo during a high-stress event. In participants whose blood pressure increased by more than average due to stressful mental task completion, L-theanine significantly inhibited blood pressure increases.
10.SupplementDEX Database: Stress — L-Theanine reduces psychological and physiological stress responses2007
A clinical study showing that L-theanine lowered psychological stress scores and decreased physiological markers such as heart rate and immunological stress responses. A study including 12 male undergraduate students found that L-theanine (200 mg) reduced salivary immunoglobulin A (s-IgA) and heart rate in response to acute stress. L-theanine may have anti-stress effects by playing an antagnoistic role in the binding of L-glutamic acid to glutamate receptors in cortical neurons, but this mechanism was not examined in this study.
SupplementDEX Database · Cognitive performance
6 references11.SupplementDEX Database: Cognitive performance — Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT2020
A crossover RCT of 5 boys with ADHD found L-theanine plus caffeine improved cognition and inhibitory control on neuroimaging tasks, though caffeine alone worsened inhibitory control.
12.SupplementDEX Database: Cognitive performance — Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis2014
A meta-analysis of 11 studies found L-theanine plus caffeine improved alertness and attentional switching in the first 2 hours, with caffeine showing stronger effects than L-theanine alone.
13.SupplementDEX Database: Cognitive performance — Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task2012
In 27 adults over a 2-hour SART vigilance task, caffeine 50 mg plus theanine 100 mg reduced error rates over time versus placebo; caffeine alone lowered tonic alpha power, but neither alone improved all attention measures.
14.SupplementDEX Database: Cognitive performance — The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness2010
In 44 young adults, L-theanine 97 mg plus caffeine 40 mg significantly improved task-switching accuracy and self-reported alertness while reducing tiredness versus placebo over 70–120 minutes.
15.SupplementDEX Database: Cognitive performance — L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness2010
In 29 adults, combined L-theanine 97 mg and caffeine 40 mg improved task-switching accuracy versus placebo; caffeine or theanine alone did not significantly change subjective alertness or intersensory attention.
16.SupplementDEX Database: Cognitive performance — The combined effects of L-theanine and caffeine on cognitive performance and mood2008
A study of 27 healthy participants found that 50 mg caffeine improved subjective alertness at 60 min following consumption and accuracy on an attention-switching task at 90 minutes following consumption. However, those taking 100 mg L-theanine in combination with caffeine improved both speed and accuracy on the attention-switching task after 60 minutes and improved focus at 60 and 90 minutes after ingestion. An L-theanine and caffeine combination may improve cognitive test performance and improve focus compared to either intervention alone.
SupplementDEX Database · Attention
3 references17.SupplementDEX Database: Attention — Dose-response effect of L-theanine on psychomotor speed, sustained attention, and inhibitory control: a double-blind, placebo-controlled, crossover study2023
A crossover RCT of 32 young adults found dose-dependent improvements in psychomotor speed and sustained attention with L-theanine (100–400 mg), with 200 mg most effective for simple tasks.
18.SupplementDEX Database: Attention — Acute effects of theanine, caffeine and theanine-caffeine combination on attention2017
A controlled trial examining acute effects of theanine, caffeine, and their combination, showing that theanine–caffeine synergistically enhanced attention measures compared with either ingredient alone. A five-way crossover study including 20 participants found that 1) L-theanine (200 mg), 2) caffeine (160 mg) and 3) L-theanine (200 mg) + caffeine (160 mg) significantly improved reaction time and attention. A group taking ceylon black tea (150 mL) did not experience improvements in reaction time. L-Theanine and caffeine had additive effects on attention. An L-theanine dose equivalent to roughly eight cups of black tea is comparable to caffeine for improving cognitive and neurophysiological measures of selective attention.
19.SupplementDEX Database: Attention — L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance2008
In 27 adults, combined L-theanine 100 mg and caffeine 50 mg reduced tonic alpha power and improved target detection in a cued attention task versus placebo, suggesting enhanced tonic visual attention deployment.
20.SupplementDEX Database: Attention deficit hyperactivity disorder (ADHD) — 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 trial2011
An RCT of 98 boys with ADHD found that 400 mg/day L-theanine for 6 weeks significantly improved sleep percentage and sleep efficiency on actigraphy versus placebo.
21.SupplementDEX Database: Age-related cognitive decline — Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study2021
A randomized placebo-controlled study showing that single-dose L-theanine improved certain measures of attention and cognitive performance in middle-aged and older adults. A 12-wk manufacturer-funded study (ITO EN, Ltd.) of 50 healthy participants (aged 50-69 yrs) comparing the effects of a single dose of L-theanine (100.6 mg) to 12-weeks of L-theanine supplementation (100.6 mg/day) found that a single dose of L-theanine was effective for reducing reaction time and improving cognitive function. After 12 weeks of regular intake, there were no changes in attention but there was a trend towards reduced reaction time.
SupplementDEX Database · Sleep
4 references22.SupplementDEX Database: Sleep — Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset2023
A crossover study found that theanine (50 mg) suppressed caffeine-induced wakefulness after sleep onset, maintaining sleep quality in healthy young women.
23.SupplementDEX Database: Sleep — Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study2023
In a crossover RCT of 16 adults, a nutritional blend with glycine, tryptophan, magnesium, and tart cherry improved self-reported sleep quality versus placebo.
24.SupplementDEX Database: Sleep — Effect of Alpha-S1-Casein Tryptic Hydrolysate and L-Theanine on Poor Sleep Quality: A Double Blind, Randomized Placebo-Controlled Crossover Trial2022
A crossover RCT of 39 adults found that alpha-s1-casein hydrolysate plus L-theanine (RLX2) for 4 weeks improved PSQI scores and prolonged total sleep time by 45 minutes versus placebo.
25.SupplementDEX Database: Sleep — Combining Topical and Oral Botanicals for Skin Redness, Pigmentation, Sleep, and Mood: A Randomized Controlled Study2022
An RCT of 75 women found that oral botanicals including L-theanine improved sleep quality at 1 and 8 weeks and reduced facial redness at 8 weeks versus topical-only treatment.
26.SupplementDEX Database: Athletic performance — The effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exercise2019
A randomized controlled study showing that L-theanine supplementation supported aspects of immune function in athletes undergoing repeated strenuous exercise. A 6-week study of 20 elite rowers found that 150 mg/day theanine contributed to significant post-exercise decreases in interleukin 10 concentration, reflected by higher interleukin 2 to IL-10 and interferon gamma to IL-10 ratios. There were no effects on lactate, time performance or white blood cell function from theanine supplementation compared to placebo.
SupplementDEX Database · Depression
2 references27.SupplementDEX Database: Depression — l-theanine adjunct to sertraline for major depressive disorder: A randomized, double-blind, placebo-controlled clinical trial2023
An RCT of 50 MDD patients found that L-theanine (200 mg/day) adjunct to sertraline significantly improved HDRS scores, with 100% response and higher remission rates at 6 weeks versus placebo.
28.SupplementDEX Database: Depression — Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study2017
An open-label study of 20 MDD patients found that 250 mg/day L-theanine for 8 weeks significantly reduced HAMD-21, anxiety, and sleep disturbance scores and improved cognitive function.
SupplementDEX Database · Influenza
1 reference29.SupplementDEX Database: Influenza — Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial2011
In 197 healthcare workers over 5 months, green tea catechins (378 mg/day) plus theanine (210 mg/day) lowered clinically defined influenza versus placebo (4.1% vs 13.1%; adjusted OR 0.25).
30.SupplementDEX Database: Mild cognitive impairment — A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study2011
In a 16-week RCT of 91 adults with mild cognitive impairment, a green tea extract and L-theanine combination improved memory and attention scores versus placebo.
31.SupplementDEX Database: Obsessive-compulsive disorder (OCD) — L-theanine combination therapy with fluvoxamine in moderate-to-severe obsessive-compulsive disorder: A placebo-controlled, double-blind, randomized trial2023
An RCT of 50 OCD patients found that 100 mg/day L-theanine adjunct to fluvoxamine significantly improved obsession subscale scores and complete response rate versus placebo.
32.SupplementDEX Database: Postoperative recovery — Perioperative Administration of Cystine and Theanine Suppresses Inflammation and Facilitates Early Rehabilitation and Recovery after Esophagectomy: A Randomized, Double-Blind, Controlled Clinical Trial2022
An RCT of 32 esophagectomy patients found that perioperative cystine and theanine reduced inflammatory markers, improved 6-minute walk distance, and shortened ICU stay versus placebo.
SupplementDEX Database · Schizophrenia
3 references33.SupplementDEX Database: Schizophrenia — L-Theanine adjunct to risperidone in the treatment of chronic schizophrenia inpatients: a randomized, double-blind, placebo-controlled clinical trial2023
An RCT of 60 schizophrenia inpatients found that 400 mg/day L-theanine adjunct to risperidone significantly reduced PANSS negative and general psychopathology scores versus placebo.
34.SupplementDEX Database: Schizophrenia — Add-On Pregnenolone with L-Theanine to Antipsychotic Therapy Relieves Negative and Anxiety Symptoms of Schizophrenia: An 8-Week, Randomized, Double-Blind, Placebo-Controlled Trial2018
An RCT of 40 schizophrenia patients found that pregnenolone plus L-theanine (50 mg/400 mg daily) significantly reduced negative symptoms and anxiety (SANS, HAM-A) versus placebo.
35.SupplementDEX Database: Schizophrenia — 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 study2011
An RCT of 60 schizophrenia patients found that 400 mg/day L-theanine for 8 weeks significantly reduced anxiety, positive symptoms, and activation factor scores versus placebo.
SupplementDEX Database · Tourette syndrome
1 reference36.SupplementDEX Database: Tourette syndrome — Use of Nutritional Supplements Based on L-Theanine and Vitamin B6 in Children with Tourette Syndrome, with Anxiety Disorders: A Pilot Study2022
An open-label RCT of 34 children with Tourette syndrome found that L-theanine plus vitamin B6 was more effective than psychoeducation for reducing tics and co-occurring anxiety symptoms.