L-Theanine

L-theanine appears to promote relaxation without sedation by modulating neurotransmitters and brain activity — increasing inhibitory signals (GABA), influencing serotonin and dopamine, reducing excitatory glutamate signaling, and increasing cortical alpha-wave activity that’s associated with a calm, alert state. These neurochemical and electrophysiological actions provide a plausible biological basis for anxiolytic (anxiety-reducing) effects. BioMed Central

Increases GABA / modulates glutamate / affects monoamines (serotonin, dopamine). Mechanistic and animal/human neurochemistry studies and reviews summarize these effects. BioMed Central

Increases alpha brain waves. Human EEG studies show greater alpha activity after L-theanine — correlated with relaxed alertness. BioMed Central

Anti-stress physiology in animal and human work. Several preclinical and clinical experiments show reduced stress biomarkers or improved stress/anxiety scores after L-theanine. Reviews summarize this mechanistic + clinical support. Worcester Research and Publications

Trials vary, but the most common clinical regimens are:

• Acute (single dose) studies: single doses in the ~50–200 mg range have been used to test immediate effects on stress, attention and EEG measures. Single-dose changes are often seen within ~30–60 minutes. BioMed Central
• Short-term daily use (several weeks): many randomized trials use 200 mg/day (e.g., 200 mg once daily) for 2–4 weeks and report improvements in stress-related symptoms and sleep measures in healthy adults. One open and other trials used doses up to 250–400 mg/day in specific contexts (some augmentation trials used higher daily doses). MDPI

Practical, evidence-based suggestions (derived from how trials were run):

• For situational/acute anxiety (exam, public speaking): single 100–200 mg taken ~30–60 minutes before the event is the regime most often evaluated. BioMed Central
• For chronic / ongoing anxiety or stress: studies have commonly used 200 mg per day (often 100 mg twice daily or 200 mg once daily) for 2–8 weeks and measured improvements. Longer or higher dose regimens (up to ~400 mg/day) appear in some research but are less common; always follow product labeling and clinician advice. MDPI

Where this comes from (examples):

• Hidese et al., Nutrients 2019 — randomized, double-blind crossover: 200 mg/day for 4 weeks in healthy adults; improvements in state/trait anxiety and sleep-related scores were reported. MDPI
• Systematic reviews list 100–400 mg/day as doses used across trials depending on acute vs. chronic designs. BioMed Central

Randomized clinical trials

• Hidese S. et al., Nutrients 2019 — Randomized, double-blind, placebo-controlled crossover in healthy adults; 200 mg/day for 4 weeks improved stress-related scores (STAI-T, SDS, PSQI). MDPI
• Sarris J. et al., Journal of Psychiatric Research 2019 — “L-theanine in the adjunctive treatment of generalized anxiety disorder”: a randomized, double-blind, placebo-controlled trial in GAD (adjunctive use). (See trial registration and article details.) BioMed Central
• Ritsner M.S. et al., Journal of Clinical Psychiatry 2011 — randomized augmentation study in schizophrenia/schizoaffective patients; L-theanine reduced anxiety symptoms when added to antipsychotics. Medscape Reference

Systematic reviews / narrative reviews

• BMC Psychiatry systematic review (2024) — systematic review of L-theanine supplementation across mental disorders (covers anxiety, schizophrenia, ADHD, OCD, mood disorders) and summarizes RCT evidence and heterogeneity across trials. Useful summary of trial quality and outcomes. BioMed Central
• Psychotropic effects review (Pharmacol Res. 2019) — a narrative/integrative review summarizing L-theanine’s clinical properties and trials for anxiety/stress and other psychiatric uses. Worcester Research and Publications

Other human experimental work

• EEG studies showing increased alpha-band power after L-theanine (supporting relaxation without sedation). BioMed Central