Amino Acid
L-Theanine
Strong EvidenceWell-replicated for acute relaxed alertness (alpha waves) and the caffeine-combination attention effect; a 4-week RCT also supports stress, sleep and executive function.
Recommended Dose
100–200 mg daily
Timing
Morning with caffeine, or evening for relaxation
Mechanism of Action
Crosses the BBB and increases alpha brain wave activity. Modulates GABA, serotonin, and dopamine. Promotes relaxed alertness by reducing excitatory glutamate activity.
Side Effects & Safety
Very well-tolerated. Extremely rare reports of mild headache or dizziness. No known serious side effects.
Do not use / talk to a doctor first
- No absolute contraindications at typical doses
- Pregnancy/breastfeeding — limited data, consult a clinician
Interactions
Blood-pressure (antihypertensive) medication
Possible additive blood-pressure lowering — monitor
Source: Yoto 2012 (PMC3518171)
Caffeine
Favourable pairing — offsets jitter and blood-pressure rise
Source: Haskell 2008 (PMID 18006208)
Prescription sedatives
Mild additive relaxation
Source: Mechanistic (GABA/glutamate modulation)
Pregnancy & breastfeeding
Limited human safety data during pregnancy and breastfeeding; keep to tea-level intake and consult a clinician before supplementing.
Who should avoid / see a doctor
Very low risk overall. Monitor if on blood-pressure medication; consult a clinician if pregnant/breastfeeding or combining with prescription sedatives. Not a treatment for a diagnosed anxiety or sleep disorder.
Synergies
Used in These Stacks
See L-Theanine inside a full protocol — the stack pages cover when and why to combine it.
Best Products
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References
- 1.Nobre 2008, Asia Pac J Clin Nutr — Increased alpha-wave activity / relaxed alertness. (short supplement article — the alpha-wave finding is the replicated core)
- 2.Haskell 2008, Biol Psychol — 250 mg L-theanine + 150 mg caffeine improved attention-switching speed and accuracy; theanine increased subjective calm.
- 3.Hidese 2019, Nutrients — 200 mg/day for 4 weeks (crossover, n=30) reduced anxiety, depression and PSQI scores and improved verbal fluency and executive function.
- 4.Yoto 2012, J Physiol Anthropol — 200 mg attenuated the stress-induced blood-pressure rise in high-stress responders — basis for the blood-pressure-medication caution.
