L-Theanine for Health & Longevity - Quick Reference Sheet
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L-Theanine for Health & Longevity

Created on 08/28/2026 – Quick Reference based on Evidence Review created using AI4L / Opus 5 – Audit

An amino acid from tea leaves producing a mild shift toward calm alertness without drowsiness. Strongest and most consistent gains: attention and reaction speed after a single dose, and reported sleep quality after weeks of daily use. Stress, mood, and blood-pressure effects are smaller and less consistent. The safety picture is unusually clean. (Full Review)

Protocol

Standard daily protocol
200 mg once or twice daily
With or without food; at least four weeks before judging effect
Situational acute protocol
Single 200 mg dose
30–60 minutes before a demanding task or stressful event; no loading period
Caffeine-pairing protocol
100–200 mg with 50–100 mg caffeine
Outperformed either alone on accuracy and self-rated alertness
Time to effect
Attention and reaction time
30–60 minutes
Appears after a single dose
Sleep quality
14–28 days
Measurable at 14 days, clearer at 28
Perceived stress
14–28 days
Measurable at 14 days, clearer at 28

Benefits

Contraindications
  • Pregnant and breastfeeding women
  • Adults with symptomatic hypotension (systolic below 90 mmHg or dizziness on standing, on 2+ antihypertensives)
  • Children with an active tic disorder, including Tourette syndrome, until clinician review
  • Anyone within 14 days of scheduled surgery under general anaesthesia
    •
Key Interactions
  • Antihypertensive drugs: lisinopril, losartan, amlodipine
  • Benzodiazepines and prescription sleep drugs: alprazolam, zolpidem
  • Over-the-counter sedating antihistamines: diphenhydramine, doxylamine
  • Sedative supplements: melatonin, valerian, kava, ashwagandha
  • Blood-pressure-lowering supplements: nitrates, garlic, hibiscus, omega-3
  • Alcohol
  • Over-the-counter stimulant and caffeine products: caffeine tablets, energy drinks
  • Other interventions: sauna, hot bathing, prolonged standing
    •

Risk & Side Effects

  • Medium: Headache; reduced total sleep time
    •
  • Low: Additive blood-pressure lowering; additive sedation; transient worsening of tics
  • Speculative: Fetal and infant exposure; potentiation of central nervous system depressants

Monitoring

Marker Target Why
Seated resting blood pressure 105–120 / 65–80 mmHg Detects additive lowering with antihypertensives
Resting heart rate 50–65 beats per minute Tracks the sympathetic calming effect
Perceived Stress Scale score Below 14 out of 40 Primary outcome used in the stress trials
Pittsburgh Sleep Quality Index score 5 or below Primary outcome in the sleep trials
Total sleep time and sleep efficiency 7–9 hours; efficiency above 85% Catches the reduced-sleep-duration signal
Morning salivary cortisol No established target; change from own baseline is tracked Objective marker of the stress response

Cadence: Baseline before the first dose; questionnaires and wearable sleep capture at 4 and 12 weeks; blood-pressure recheck at 2 and 12 weeks where antihypertensives are in use; annual thereafter.

Qualitative Assessment

  • Subjective calm without drowsiness during demanding work
  • Ease of falling asleep and how refreshed waking feels
  • Whether caffeine produces less restlessness at the same intake
  • Cognitive clarity and ability to ignore distraction
  • Absence of next-morning sedation
Not medical advice. Educational distillation of a single evidence review. Confirm any decision with a qualified clinician, especially in the presence of prescription drugs or chronic conditions.