In a double-blind, placebo-controlled, balanced crossover study, the effects of 200 mg L-theanine on stress were measured using magnetoencephalography (MEG). Participants (n=34) were put under stressful scenarios and evaluated for markers of stress, including brain waves, salivary cortisol and the State-Trait Anxiety Inventory questionnaire. Two hours after administration those categorized as “high anxiety” showed a significant increase in alpha brain waves compared to the placebo group. Alpha waves are characterized by a relaxed wakefulness, while beta waves are typical in highly stressful situations.
White DJ, de Klerk S, Woods W, Gondalia S, Noonan C, Scholey AB. Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial. Nutrients. 2016 Jan 19;8(1):53. doi: 10.3390/nu8010053. PMID: 26797633; PMCID: PMC4728665.