L-Theanine
L-theanine is an amino acid found in tea leaves, sold as a supplement for calm focus and stress reduction. It promotes relaxation without sedation, is often paired with caffeine to smooth stimulation, and increases alpha brainwave activity. Human evidence is modest but positive, and its safety margin is wide with no known dependence.
01 Overview
L-theanine crosses the blood-brain barrier and is one of the better-studied calming supplements, with several small randomised trials on acute stress, subjective relaxation and attention. Effects are subtle rather than dramatic.
It is commonly combined with caffeine, where the pairing improves attention and reduces jitteriness compared with caffeine alone. It is well tolerated with no meaningful abuse or withdrawal liability.
02 Mechanism
Structural analogue of glutamate that modestly modulates glutamatergic and GABAergic transmission, raises GABA, dopamine and serotonin in animal models, and increases cortical alpha-wave activity associated with relaxed alertness.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Calm focus | 100–200 mg | Oral | Often paired 1:1 or 2:1 with caffeine (e.g. 200 mg with 100 mg caffeine). |
| Acute stress | 200–400 mg | Oral | Higher single doses used in stress-response studies. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Relaxation without sedationIncreases subjective calm and alpha-wave activity while preserving alertness. | Mild-moderate | Clinical | |
| Reduced acute stress responseBlunts heart-rate and cortisol responses to stressful tasks in small trials. | Mild | Clinical | |
| Smoother caffeine stimulationCombined with caffeine, improves attention and reduces jitteriness versus caffeine alone. | Moderate | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Mild drowsinessOccasional light sedation, mainly at higher doses without caffeine. | Mild | Uncommon | Anecdotal | |
| HeadacheOccasional headache reported at higher doses. | Mild | Rare | Anecdotal |