The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review

What this study found

Overall, L-theanine showed a modest beneficial effect for acute stress and anxiety, especially at 200-400 mg/day, but evidence for chronic anxiety conditions was inconsistent. In healthy or stressed participants, L-theanine reduced heart rate, improved anxiety-related ratings, and lowered stress responses in several studies, including reduced HARS in schizophrenia or schizoaffective disorder (p = 0.015), lower psychosocial stress and salivary alpha-amylase in pharmacy students (p = 0.020 and p = 0.032), and decreased tension-anxiety scores in an acute stress study (p = 0.004). However, the…

Study & population

Systematic review of 9 studies including 270 participants.

Intervention

Pure L-theanine was evaluated across 9 human studies at doses ranging from 200 mg as a single acute dose to 400 mg/day for 8 weeks, with one anxiety trial escalating from 225 mg twice daily to 450 mg twice daily at week 4.

Key limitation

The evidence base was small and heterogeneous, with mixed healthy and clinical populations, differing doses, short follow-up in most studies, and varied stress and anxiety measures.

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