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Summary
L‑theanine is a non‑protein amino acid found primarily in tea leaves. In healthy adults, it modestly promotes calm alertness, reduces subjective stress, and can improve attention and sleep quality in select contexts. Evidence supports synergy with low‑to‑moderate caffeine for focus with fewer jitters.
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Theanine — Thorne
An amino acid from tea that supports a healthy stress response, relaxation, focus, and memory. NSF Certified for Sport®.
Mental Clarity, Focus, and Energy
- RCTs show that 100–200 mg theanine can improve selective attention and reaction time, especially when combined with ~50–150 mg caffeine.
- EEG findings often show increased alpha‑band activity consistent with relaxed alertness within 30–60 minutes of dosing.
- Benefits are most consistent for attention under stress or fatigue; effects are smaller on complex executive tasks when used alone.
- Heterogeneity: habitual caffeine use, stress level, and timing influence outcomes.
Brain Health
- Mechanisms: modulates glutamatergic signaling, increases GABA and dopamine in some models, and may reduce sympathetic arousal.
- Human data for long‑term neuroprotection are limited; current strength of evidence is in acute anxiolysis and attentional measures rather than disease modification.
Gut Health
- Generally well tolerated. Limited human data suggest low GI adverse event rates at typical doses.
- Direct microbiome or barrier effects in humans are not well established; most signals are indirect via stress‑autonomic pathways.
Brain-Gut Axis
- By lowering perceived stress and sympathetic tone, theanine may indirectly benefit gut–brain communication in stress‑sensitive GI symptoms. Evidence is suggestive but not definitive.
Evidence Summary
Benefit Area | Evidence Quality | Effect Noted | Notes |
Mental Clarity | Moderate | Improved attention under stress | 100–200 mg; stronger with caffeine |
Focus Enhancement | Moderate | Faster reaction time with L‑theanine+caffeine | Synergy at 1:1 to 2:1 ratios |
Energy Support | Limited | Perceived calm energy, not stimulant‑like | Best as adjunct to caffeine |
Brain Health | Limited | Mechanistic anxiolysis, limited long‑term data | No disease‑modification trials |
Gut Health | Limited | Low GI adverse events | Minimal direct human data |
Brain–Gut Optimization | Emerging | Stress reduction may aid gut symptoms | Indirect evidence |
Typical Dosing Instructions
- Standard dose: 100–200 mg once or twice daily
- Timing: Evening for sleep, or 30–60 minutes before focus tasks
- Form: Standalone capsule or combined with caffeine for task performance
- Notes: Common stack is 100–200 mg theanine with ~50–150 mg caffeine; adjust ratio based on jitter sensitivity
Safety Considerations
- General safety: Generally well tolerated at typical supplemental doses
- Common effects: Relaxation, reduced jitters with caffeine; occasional sleepiness at higher doses
- Contraindications and cautions: Additive effects with sedatives or other calming agents; theoretical BP‑lowering interaction with antihypertensives
- Populations: Limited data in pregnancy or pediatrics; avoid unless clinician‑directed
- Monitoring: Track daytime sleepiness, task performance, and sleep latency; reduce dose if grogginess occurs
References
- Effects of Tea or L‑Theanine or L‑Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta‑analysis of RCTs, Nutrients, 2025-01-10
- Acute effects of L‑theanine, caffeine, and EGCG on cognitive function and mood: a systematic review and meta‑analysis, Nutrition Reviews, 2014-08-01
- The combined effects of L‑theanine and caffeine on cognitive performance and mood, Nutritional Neuroscience, 2008-01-01
- The combination of L‑theanine and caffeine improves cognitive performance and increases subjective alertness, Biological Psychology, 2008-01-01