L-Theanine reduces psychological and physiological stress responses

Biol Psychol. 2007 Jan;74(1):39-45. doi: 10.1016/j.biopsycho.2006.06.006. Epub 2006 Aug 22.


L-Theanine is an amino acid contained in green tea leaves which is known to block the binding of L-glutamic acid to glutamate receptors in the brain. Because the characteristics of L-Theanine suggest that it may influence psychological and physiological states under stress, the present study examined these possible effects in a laboratory setting using a mental arithmetic task as an acute stressor. Twelve participants underwent four separate trials: one in which they took L-Theanine at the start of an experimental procedure, one in which they took L-Theanine midway, and two control trials in which they either took a placebo or nothing. The experimental sessions were performed by double-blind, and the order of them was counterbalanced. The results showed that L-Theanine intake resulted in a reduction in the heart rate (HR) and salivary immunoglobulin A (s-IgA) responses to an acute stress task relative to the placebo control condition. Moreover, analyses of heart rate variability indicated that the reductions in HR and s-IgA were likely attributable to an attenuation of sympathetic nervous activation. Thus, it was suggested that the oral intake of L-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Acute Disease
  • Adult
  • Brain / metabolism
  • Cognition / drug effects
  • Double-Blind Method
  • Electrocardiography
  • Female
  • Glutamates / pharmacology*
  • Glutamic Acid / drug effects
  • Glutamic Acid / metabolism
  • Heart Rate / drug effects
  • Humans
  • Immunoglobulin A / analysis
  • Male
  • Neural Inhibition / drug effects
  • Psychoneuroimmunology / methods*
  • Receptors, Glutamate / metabolism
  • Saliva / chemistry
  • Stress, Psychological / drug therapy*
  • Stress, Psychological / immunology*
  • Sympathetic Nervous System / drug effects


  • Glutamates
  • Immunoglobulin A
  • Receptors, Glutamate
  • Glutamic Acid
  • theanine