Clinical Evidence: How L-Theanine Modulates Brain Waves and Cortisol Levels

A 2021 clinical trial published in Neurology and Therapy utilized a triple-blind, placebo-controlled crossover design—the highest standard in clinical research—to evaluate the impact of a single 200 mg dose of L-theanine on the human stress response. The study monitored 16 healthy adults (ages 18–60) to determine how the amino acid affects both neurological activity and hormonal markers.

The researchers observed two primary physiological outcomes:

• Neurological Shift: Within three hours of administration, participants showed a significant increase in Alpha power across the frontal region and the whole scalp. Alpha brain waves are specifically associated with a state of "relaxed alertness," indicating a reduction in mental anxiety without a corresponding increase in drowsiness.

• Hormonal Regulation: The study recorded a statistically significant decrease in salivary cortisol levels just one hour after ingestion. Cortisol is the body’s primary stress hormone; its reduction suggests that L-theanine can rapidly downregulate the physiological "fight or flight" response.

Crucially, the study found no significant changes in heart rate compared to the placebo group, concluding that L-theanine provides a calming effect through central nervous system modulation rather than through cardiovascular sedation. These findings support the use of L-theanine as an effective, non-drowsy intervention for managing acute psychological stress.

Article: A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave® l-Theanine on Stress in a Healthy Adult Population https://pubmed.ncbi.nlm.nih.gov/34562208/