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. 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.
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.
Reduces Stress and Anxiety
By modulating neurotransmitters like GABA and serotonin, L-Theanine may reduce stress and anxiety symptoms, helping to calm the mind.
Improves Focus and Attention
L-Theanine, often paired with caffeine, enhances cognitive performance by improving focus and attention while reducing jitteriness.
Enhances Sleep Quality
L-Theanine may improve sleep by promoting relaxation and reducing anxiety, helping with faster sleep onset and better rest.
Supports Cognitive Function
By protecting neurons from oxidative stress and modulating glutamate, L-Theanine may support memory and cognitive health, though evidence is preliminary.
Mood Improvement
L-Theanine may elevate mood by increasing serotonin and dopamine levels, potentially alleviating mild depressive symptoms.
Cardiovascular Health Support
L-Theanine may lower blood pressure and heart rate during stress, contributing to cardiovascular health, though data is limited.
Immune System Modulation
L-Theanine may enhance immune function by supporting anti-inflammatory responses and increasing glutathione levels, but more research is needed.
Mechanism of Action
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.
Modulates Neurotransmitters
It enhances levels of GABA, serotonin, and dopamine by inhibiting excitatory neurotransmitters like glutamate, promoting relaxation and reducing stress.
Reduces Glutamate Excitotoxicity
L-Theanine binds to glutamate receptors, reducing excitotoxicity and protecting neurons from damage, which may support cognitive health.
Synergizes with Caffeine
When combined with caffeine, L-Theanine enhances dopamine release and modulates adenosine receptors, improving focus and attention while reducing jitteriness.
Lowers Stress Response
L-Theanine inhibits cortisol release and reduces sympathetic nervous system activity, lowering heart rate and blood pressure during stress.
Improves Sleep Regulation
By increasing GABA and reducing excitatory signaling, L-Theanine promotes relaxation, facilitating faster sleep onset and better sleep quality.
Antioxidant Effects
L-Theanine may increase glutathione levels, reducing oxidative stress and supporting neuronal and immune health, though mechanisms are not fully elucidated.
Anti-Inflammatory Effects
L-Theanine modulates cytokine production, potentially reducing inflammation, which may contribute to its immune and cardiovascular benefits.
Clinical Trials
L-Theanine in the Adjunctive Treatment of Generalized Anxiety Disorder: A Double-Blind, Randomised, Placebo-Controlled Trial
Study: This RCT involved 46 patients with generalized anxiety disorder (GAD), randomized to receive L-Theanine (450–900 mg/day) or placebo for 8 weeks as an adjunct to current antidepressant therapy. Outcomes included anxiety scores (Hamilton Anxiety Rating Scale), insomnia, and cognitive function.
Findings: L-Theanine significantly improved insomnia scores (p=0.007) but showed no significant effect on anxiety scores compared to placebo. Benefits were independent of anxiety severity changes, suggesting a specific effect on sleep.
Link: https://www.sciencedirect.com/science/article/abs/pii/S0022395618313261[](https://link.springer.com/article/10.1007/s40120-021-00284-x)
Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
Study: A double-blind, placebo-controlled crossover trial with 30 healthy Japanese adults (no major psychiatric disorders) assessed L-Theanine (200 mg/day for 4 weeks) versus placebo. Outcomes included stress (Self-rating Depression Scale, STAI-trait), sleep (PSQI), and cognitive function (BACS).
Findings: L-Theanine significantly improved depression (p=0.019), anxiety (p=0.006), and sleep quality (p=0.013), particularly sleep latency and daytime dysfunction. Letter fluency improved significantly (p=0.001), but other cognitive scores showed no significant difference compared to placebo.
Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836118/[](https://pmc.ncbi.nlm.nih.gov/articles/PMC6836118/)
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
Study: This RCT evaluated L-Theanine (400 mg/day) versus placebo in 98 boys (aged 8–12) with ADHD over 6 weeks, measuring sleep quality via actigraphy and parent-reported sleep scales.
Findings: L-Theanine significantly improved sleep efficiency and reduced sleep disturbances compared to placebo, with no significant adverse effects, suggesting benefits for ADHD-related sleep issues.
Link: https://pubmed.ncbi.nlm.nih.gov/22214254/[](https://www.mskcc.org/cancer-care/integrative-medicine/herbs/l-theanine)
A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave® L-Theanine on Stress
Study: This crossover RCT involved 16 healthy adults with moderate stress, receiving a single dose of AlphaWave® L-Theanine (200 mg) or placebo. Stress was induced via a mental arithmetic test, with outcomes including EEG alpha power, salivary cortisol, and subjective stress.
Findings: L-Theanine significantly increased alpha power (indicating relaxation) and reduced salivary cortisol and subjective stress one hour post-dose (p<0.05), supporting acute stress-reducing effects. No cognitive performance differences were noted.
Link: https://link.springer.com/article/10.1007/s40120-021-00284-x[](https://link.springer.com/article/10.1007/s40120-021-00284-x)
Safety and Efficacy of AlphaWave® L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial
Study: This RCT randomized 30 healthy adults with moderate stress to AlphaWave® L-Theanine (400 mg/day) or placebo for 28 days. Outcomes included stress (Perceived Stress Scale, DASS-21), sleep (PSQI, actigraphy), cognition, and mood (POMS).
Findings: No significant between-group differences were found in stress, sleep, or cognitive outcomes, possibly due to a strong placebo effect. L-Theanine was safe with no adverse events, but efficacy was not superior to placebo.
Link: https://link.springer.com/article/10.1007/s40120-024-00625-6[](https://link.springer.com/article/10.1007/s40120-024-00624-7)
Effects of L-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study
Study: A double-blind RCT with 30 Japanese adults (aged 50–69) examined L-Theanine (single dose and 200 mg/day for 12 weeks) versus placebo, using Cognitrax to assess attention, working memory, and executive function.
Findings: A single dose reduced reaction time in attention tasks (Stroop test, p<0.05) and improved accuracy in working memory tasks (p<0.05). After 12 weeks, L-Theanine enhanced attention and working memory, suggesting cognitive benefits in aging populations.
Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8080935/[](https://pmc.ncbi.nlm.nih.gov/articles/PMC8080935/)
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
Study: This RCT involved 60 patients with schizophrenia or schizoaffective disorder, receiving L-Theanine (400 mg/day) or placebo for 8 weeks alongside antipsychotics. Outcomes included Positive and Negative Syndrome Scale (PANSS) scores and anxiety.
Findings: L-Theanine significantly reduced anxiety, positive symptoms, and general psychopathology (p<0.05), with increased BDNF levels, suggesting adjunctive benefits in schizophrenia.
Link: https://pubmed.ncbi.nlm.nih.gov/21208586/[](https://www.mskcc.org/cancer-care/integrative-medicine/herbs/l-theanine)
L-Theanine Adjunct to Sertraline for Major Depressive Disorder: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial
Study: This RCT assessed L-Theanine (250 mg/day) versus placebo as an adjunct to sertraline in 46 patients with major depressive disorder (MDD) over 8 weeks, measuring depression (Hamilton Depression Rating Scale) and anxiety scores.
Findings: L-Theanine significantly reduced depression and anxiety scores (p<0.05) compared to placebo, suggesting it enhances antidepressant effects in MDD.
Link: https://www.sciencedirect.com/science/article/abs/pii/S0165032723004777[](https://x.com/skitterspatial/status/1927925093335978059)
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.
Drug Interactions
L-Theanine may enhance the effects of sedatives, antidepressants, or stimulants (e.g., caffeine), potentially altering their efficacy or causing side effects.