L-theanine
γ-glutamylethylamide
Also known as: Theanine, 5-N-ethylglutamine, Suntheanine, L-γ-glutamylethylamide
L-theanine is an amino acid found primarily in green tea that promotes relaxation without drowsiness. It increases alpha brain wave activity associated with calm alertness.
Introduction
L-theanine is a unique amino acid primarily found in the leaves of Camellia sinensis, the tea plant. It was discovered in 1949 by Japanese scientists and is responsible for the characteristic umami flavor of green tea. Unlike most amino acids, L-theanine is not used to build proteins but instead functions as a bioactive compound with psychoactive properties.
L-theanine is structurally similar to the neurotransmitter glutamate and can cross the blood-brain barrier. Once in the brain, it exerts several effects including increasing alpha brain wave activity (associated with relaxed alertness), modulating neurotransmitter levels, and promoting relaxation without causing sedation.
The combination of L-theanine and caffeine, naturally present in tea, has been extensively studied. Research suggests that L-theanine can smooth out some of the jittery effects of caffeine while preserving its cognitive benefits, creating a state of "calm focus."
Beyond its cognitive effects, L-theanine has been studied for stress reduction, blood pressure lowering, immune support, and sleep improvement. It has an excellent safety profile with no known toxicity, even at high doses.
L-theanine supplements are typically produced through fermentation or extraction processes. Synthetic forms exist, but most supplements aim to replicate the natural L-isomer found in tea.
Main Benefits
Promotes relaxation and reduces stress without causing drowsiness or sedation.
Increases alpha brain wave activity associated with relaxed alertness and selective attention.
May improve cognitive performance and attention, particularly when combined with caffeine.
Reduces blood pressure increases during stressful situations.
May improve sleep quality and reduce sleep disturbances.
Mechanism of Action
L-theanine exerts its effects through multiple neurochemical mechanisms:
Alpha Wave Enhancement: L-theanine increases alpha brain wave activity (8-13 Hz), which is associated with a state of "relaxed alertness" - calm but awake and attentive. This is measurable via EEG within 30-40 minutes of ingestion.
Glutamate Receptor Modulation: L-theanine is structurally similar to glutamate and can bind to glutamate receptors (AMPA, kainate, and NMDA) as a weak antagonist. This may protect neurons from glutamate excitotoxicity while maintaining normal function.
Neurotransmitter Effects: L-theanine increases levels of GABA, serotonin, and dopamine in the brain. These changes in neurotransmitter balance promote relaxation and positive mood.
Caffeine Synergy: When combined with caffeine, L-theanine appears to enhance cognitive benefits while reducing caffeine-induced jitters, anxiety, and blood pressure increases. This synergistic effect may involve modulation of caffeine's vasoconstrictive effects.
Cortisol Reduction: L-theanine may reduce cortisol responses to stress, potentially explaining its anxiolytic effects.
Blood Pressure Modulation: L-theanine appears to attenuate blood pressure increases during stressful tasks, possibly through its relaxing effects and nitric oxide-related mechanisms.
Natural Sources
L-theanine is found naturally in tea leaves, particularly green tea. Black tea contains less due to oxidation during processing.
Examples:
Green tea (highest concentration)
White tea
Black tea (lower concentration)
Oolong tea
Some mushrooms (Boletus badius)
Green tea provides 25-60 mg per cup; easy to obtain through tea consumption; supplements offer higher doses (100-400 mg).
Recommended Daily Intake
No established RDA. Typical doses range from 100-400 mg daily. Effects on alpha waves seen at 50-200 mg. Studies use 200-400 mg for stress and cognitive effects.
Reference Values:
| Relaxation | 100-200 mg |
| Stress reduction | 200-400 mg/day |
| With caffeine | 100-200 mg L-theanine per 100 mg caffeine |
| Sleep support | 200-400 mg before bed |
Sources for RDI/AI:
Can be taken any time of day as it does not cause drowsiness. Take 30-60 minutes before desired effect. Very safe even at high doses.
Effectiveness for Specific Focuses
Promotes relaxation without sedation; reduces cortisol; increases alpha waves; excellent for stress management without impairment.
Enhances attention and focus; synergistic with caffeine; alpha wave activity supports cognitive performance.
Promotes calm and positive mood; increases serotonin and dopamine; anxiolytic effects without sedation.
Improves sleep quality without causing drowsiness; may help with falling asleep and sleep depth; stress reduction supports sleep.
Safety Information
Potential Side Effects
Very rarely: headache
Very rarely: dizziness
Generally extremely well-tolerated
Contraindications
None well-established
Use caution with hypotension (may lower blood pressure)
Overdose Information
Exceptional safety profile; no toxicity observed even at very high doses; GRAS status by FDA; no known lethal dose.
One of the safest supplements available. No adverse effects reported at any tested dose. Safe for children and adults.
Interactions
Drug Interactions:
Blood pressure medications (may enhance effects)
Stimulants (may reduce side effects of caffeine)
Very low risk; may enhance effects of BP medications; reduces caffeine side effects; generally safe with all medications.
Other Supplement Interactions:
Caffeine - synergistic cognitive enhancement with reduced jitters
GABA - may be synergistic for relaxation
Melatonin - may complement for sleep
Synergistic with caffeine; very safe with all supplements.
Extremely safe supplement with no significant warnings. Can be taken any time of day. May enhance effects of blood pressure medications.
Forms and Bioavailability
Most L-theanine supplements are produced through fermentation to replicate the natural form. Suntheanine is a patented form.
L-theanine (fermented)
Naturally identical form produced through fermentation; excellent bioavailability; crosses blood-brain barrier efficiently.
Well-absorbed; crosses blood-brain barrier effectively; effects seen within 30-40 minutes.
Standard form in most supplements. Fermentation produces the same L-isomer found in tea. Very reliable.
Suntheanine
Patented pure L-theanine produced through fermentation; well-researched; high purity.
High purity; extensive research backing; patented production ensures consistent quality.
Patented form with published research backing efficacy. Considered premium quality. No significant advantage over other quality sources.
Green Tea Extract
Contains L-theanine along with other tea compounds including caffeine and catechins.
Natural source with synergistic compounds; lower theanine concentration per dose.
Provides the natural matrix of tea compounds. Lower L-theanine content than pure supplements but includes synergistic catechins and caffeine.
Warnings & Suitability
Did You Know...?
L-theanine is responsible for the umami (savory) taste of green tea, often described as brothy or seaweed-like.
The ratio of L-theanine to caffeine in tea is thought to explain why tea provides a smoother, more sustained energy boost than coffee.
Shade-grown tea plants (like those used for matcha and gyokuro) produce significantly more L-theanine than sun-grown plants.
L-theanine increases alpha brain waves, the same brain wave pattern seen during meditation and REM sleep.
General Scientific Sources
Tags
Content Verification
Last Medical Review: 2/13/2026
Reviewed by: Editorial Team