<sec id="S0924270816000338_abs1" sec-type="general"><title>Objective</title><sc>l</sc>-theanine, an amino acid uniquely contained in green tea (<italic>Camellia sinensis</italic>), has been suggested to have various psychotropic effects. This study aimed to examine whether <sc>l</sc>-theanine is effective for patients with major depressive disorder (MDD) in an open-label clinical trial.

</sec><sec id="S0924270816000338_abs2" sec-type="methods"><title>Methods</title>Subjects were 20 patients with MDD (four males; mean age: 41.0±14.1 years, 16 females; 42.9±12.0 years). <sc>l</sc>-theanine (250 mg/day) was added to the current medication of each participant for 8 weeks. Symptoms and cognitive functions were assessed at baseline, 4, and 8 weeks after <sc>l</sc>-theanine administration by the 21-item version of the Hamilton Depression Rating Scale (HAMD-21), State-Trait Anxiety Inventory (STAI), Pittsburgh Sleep Quality Index (PSQI), Stroop test, and Brief Assessment of Cognition in Schizophrenia (BACS).

</sec><sec id="S0924270816000338_abs3" sec-type="results"><title>Results</title>HAMD-21 score was reduced after <sc>l</sc>-theanine administration (<italic>p</italic>=0.007). This reduction was observed in unremitted patients (HAMD-21&gt;7; <italic>p</italic>=0.004) at baseline. Anxiety-trait scores decreased after <sc>l</sc>-theanine administration (<italic>p</italic>=0.012) in the STAI test. PSQI scores also decreased after <sc>l</sc>-theanine administration (<italic>p</italic>=0.030) in the unremitted patients at baseline. Regarding cognitive functions, response latency (<italic>p</italic>=0.001) and error rate (<italic>p</italic>=0.036) decreased in the Stroop test, and verbal memory (<italic>p</italic>=0.005) and executive function (<italic>p</italic>=0.016) were enhanced in the BACS test after <sc>l</sc>-theanine administration.

</sec><sec id="S0924270816000338_abs4" sec-type="conclusion"><title>Conclusion</title>Our study suggests that chronic (8-week) <sc>l</sc>-theanine administration is safe and has multiple beneficial effects on depressive symptoms, anxiety, sleep disturbance and cognitive impairments in patients with MDD. However, since this is an open-label study, placebo-controlled studies are required to consolidate the effects.

</sec>