L-Theanine

Also known as: theanine, suntheanine, γ-glutamylethylamide

Grade B — Moderate Evidenceamino acidnootropic

Recommended Dosage

100–400 mg

Morning with caffeine for focus; evening for sleep

L-Theanine is an amino acid found almost exclusively in tea leaves (Camellia sinensis). It promotes a state of calm alertness by increasing alpha brain wave activity — the same pattern seen during meditation. When combined with caffeine, it creates a synergistic effect: sustained attention and focus without the jitteriness or crash of caffeine alone. This makes the L-Theanine + caffeine stack one of the most well-validated nootropic combinations.

TL;DR: Amino acid from green tea. Promotes calm focus (alpha brain waves) without drowsiness. Excellent safety profile.

🎯Focus🧘Stress & Anxiety🌙Sleep🧠Cognitive Performance
Last reviewed: 2026-03-09

Evidence Rating: Grade B — Moderate Evidence

Some RCTs with positive results, or strong observational evidence. More research may refine our understanding.

Interaction Warnings

Blood pressure medicationsLow

May enhance BP lowering effects slightly

Stimulants (Adderall, modafinil)Low

Theanine may blunt some stimulant effects

⚠️ Important Notes

  • Very well tolerated
  • Synergistic with caffeine for focus without jitters
  • Not sedating; does not impair driving

Clinical Evidence (3 studies)

L-theanine and caffeine improve cognitive performance

Nobre AC et al. (2008) — Asia Pac J Clin Nutr

L-theanine and caffeine improve cognitive performance and increase alertness

View on PubMed

L-theanine reduces psychological and physiological stress

Kimura K et al. (2007) — Biol Psychol

L-theanine reduces stress responses

View on PubMed

Theanine + caffeine improve attention-switching

Owen GN et al. (2008) — Nutr Neurosci

Improved speed and accuracy on attention-switching tasks

View on PubMed

Related Supplements

Bacopa Monnieri

Grade B — Moderate Evidence

Ayurvedic herb with strong meta-analytic evidence for memory and learning. Requires consistent use for 8-12 weeks.

Phosphatidylserine

Grade B — Moderate Evidence

Phospholipid that supports cell membrane integrity in the brain. FDA-qualified health claim for cognitive decline. Reduces cortisol.

Magnesium L-Threonate

Grade B — Moderate Evidence

The only magnesium form shown to cross the blood-brain barrier effectively. Promising for cognitive function and brain aging.

Lemon Balm

Grade B — Moderate Evidence

Gentle anxiolytic herb that provides calmness without sedation. Pairs well with valerian for sleep. Watch thyroid interactions.

🧪 Get Your Personalized Stack

See how L-Theanine fits with your goals and current supplements — AI-powered, evidence-graded recommendations.

⚕️ Important Disclaimer

This information is for educational purposes only. It is not medical advice. Always consult a healthcare provider before starting any supplement regimen, especially if you take medications or have health conditions.

Evidence Stack does not sell supplements and has no affiliate relationships with supplement manufacturers.