Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-theanine is an amino acid found primarily in green tea. Its use in supporting or treating depression is justified by emerging scientific evidence, though it is not yet robust. Several small clinical studies and animal research indicate that L-theanine may have mood-modulating effects. Mechanistically, L-theanine is believed to increase levels of neurotransmitters such as serotonin, dopamine, and GABA, all of which play roles in mood regulation. It also appears to have anxiolytic (anxiety-reducing) effects and may reduce psychological stress, which often co-occurs with depression. A few randomized controlled trials have explored L-theanine supplementation in people with depressive symptoms. For example, a 2017 open-label study found that 250 mg/day of L-theanine for 8 weeks improved scores on depression, anxiety, and sleep quality scales. However, this study had a small sample size and lacked a placebo group. Other research has focused on L-theanine's ability to improve cognitive function and reduce stress in healthy adults, which may indirectly benefit those with depression. In summary, while there is some promising preliminary evidence that L-theanine may help alleviate depressive symptoms, the quality and quantity of clinical research are still limited. Larger, well-designed placebo-controlled trials are needed to confirm its efficacy. At present, L-theanine should be considered a potential adjunct to, but not a replacement for, established depression treatments.

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