Abstract
Recent evidence suggests that greater green tea consumption is associated with a reduced risk of psychiatric diseases such as depressive disorder. Theanine (L-theanine or L-γ-glutamylethylamide) , an amino acid uniquely contained in green tea, is known as a relaxing agent which has a chemical structure similar to glutamate. In our animal experiments, theanine improved sensorimotor gating as assessed with prepulse inhibition [PPI] and showed an antidepressant-like effect such as shortening the immobility time in the forced swimming test and upregulation of brain derived neurotrophic factor in the hippocampus. We found that single administration of theanine (200 or 400 mg) increased PPI in healthy individuals. Administration of theanine for 8 weeks mitigated positive symptoms and sleep quality in chronic schizophrenia patients. In an 8-week open-label study on major depressive disorder, theanine improved depressed mood, anxiety, sleep and cognitive function. These findings suggest that theanine has various psychotropic effects and is useful in the treatment of psychiatric disorders including schizophrenia and depressive disorder.
