L-Theanine reduces psychological and physiological stress responses

This randomized, placebo-controlled study examined L-theanine's effects on stress responses in 12 healthy adults during a mental arithmetic stressor. Participants received either 200mg of L-theanine or placebo.

Results showed that L-theanine significantly reduced both psychological and physiological stress responses. Heart rate and salivary immunoglobulin A responses to stress were attenuated in the L-theanine group, indicating reduced sympathetic nervous system activation.

Participants receiving L-theanine also reported feeling calmer and more relaxed during the stressful task without experiencing sedation or impaired performance. The study provides objective evidence for L-theanine's anti-stress effects and supports its traditional use in tea for promoting relaxation. L-theanine appears to promote alpha brain wave activity associated with relaxed alertness while modulating neurotransmitters including GABA, serotonin, and dopamine. Effects were observed within 30-40 minutes of administration.