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Effect of l-theanine on glutamatergic function in patients with schizophrenia

Objectives Glutamatergic dysfunction in the brain has been implicated in the pathophysiology of schizophrenia. Previous studies suggested that l-theanine affects the glutamatergic neurotransmission and ameliorates symptoms in patients with schizophrenia. The aims of the present study were twofold: to examine the possible effects of l-theanine on symptoms in chronic schizophrenia patients and to evaluate the changes in chemical mediators, including glutamate + glutamine (Glx), in the brain by using 1H magnetic resonance spectroscopy (MRS). Method The subjects were 17 patients with schizophrenia and 22 age- and sex-matched healthy subjects. l-Theanine (250 mg/day) was added to the patients’ ongoing antipsychotic treatment for 8 weeks. The outcome measures were the Positive and Negative Syndrome Scale (PANSS), Pittsburgh Sleep Quality Index scores and MRS results. Results There were significant improvements in the PANSS positive scale and sleep quality after the l-theanine treatment. As for MRS, we found no significant differences in Glx levels before and after the 8 week l-theanine treatment. However, significant correlations were observed between baseline density of Glx and change in Glx density by l-theanine. Conclusions Our results suggest that l-theanine is effective in ameliorating positive symptoms and sleep quality in schizophrenia. The MRS findings suggest that l-theanine stabilises the glutamatergic concentration in the brain, which is a possible mechanism underlying the therapeutic effect.