L-Theanine

• Stress/anxiety: Research suggests L-theanine may reduce subjective stress and state anxiety and dampen physiological stress responses (e.g., heart rate, salivary alpha-amylase). Evidence is moderate (multiple small-to-midsize RCTs; several systematic reviews). Effects are generally small-to-moderate and may be more noticeable in higher-stress individuals.
• Attention and cognitive performance: Strongest evidence is for L-theanine combined with caffeine, which improves attention, reaction time, and accuracy while reducing caffeine-related jitter. Evidence is strong for the combination (meta-analyses) and emerging-to-moderate for L-theanine alone.
• Sleep quality: May improve sleep quality and reduce sleep latency, particularly in people with stress/anxiety or in children with ADHD. Evidence is moderate but based on small RCTs; effect sizes are generally small.
• Blood pressure under stress: May blunt stress-induced increases in blood pressure and slightly lower resting blood pressure in people with high stress reactivity. Evidence is emerging (small RCTs).
• Adjunct in schizophrenia: As an add-on to antipsychotics, some studies show reduced anxiety and certain symptom scores at 400 mg/day. Evidence is emerging (small RCTs).

Generally well tolerated in clinical studies.

• Common (typically mild): headache, dizziness, gastrointestinal upset, mild drowsiness or sedation (usually dose-related).
• Less common: lowered blood pressure or lightheadedness, especially in those with low baseline BP or on antihypertensives; agitation or vivid dreams have been reported rarely.
• Rare: allergic reactions (rash, itching).
• No consistent evidence that isolated L-theanine affects coagulation; bleeding effects reported with green tea extracts are not attributed to L-theanine itself.

Commonly used ranges in studies (not prescriptive):

• General relaxation/stress: 100–400 mg/day, often divided, for 4–8 weeks; acute doses of 100–200 mg taken 30–60 minutes before a stressor/task are common in lab studies.
• Attention/cognition with caffeine: 100–200 mg L-theanine paired with 40–160 mg caffeine (ratios ~1:1 to 2:1 theanine:caffeine) taken acutely.
• Sleep quality: 200–400 mg/day, typically in late afternoon or evening, for several weeks in small trials.
• Adjunct in schizophrenia: 400 mg/day in divided doses in RCTs. Optimal dosing varies by individual, goal, and sensitivity; start low and adjust with clinician guidance.

• Hypotension or episodes of low blood pressure: may further lower BP.
• Pre-surgical: due to potential BP and CNS effects, stop 1–2 weeks before surgery unless physician advises otherwise.
• Pregnancy and breastfeeding: human data are limited; avoid or use only under medical supervision.
• Severe hepatic or renal impairment: limited safety data—use caution and consult a clinician.
• Concomitant CNS depressants (e.g., benzodiazepines, sedative-hypnotics) or stimulants (e.g., amphetamines, methylphenidate): use cautiously due to potential additive or opposing CNS effects.
• Children/adolescents: some data exist (e.g., ADHD sleep RCT), but broader pediatric safety data are limited—consult a pediatric clinician.
• Note: Pure L-theanine has no known direct interaction with anticoagulants; however, green tea extracts (not theanine itself) have been reported to affect warfarin—verify product contents.