Green tea (Camellia sinensis) has been investigated for its potential to support or treat depression, primarily due to its bioactive compounds such as L-theanine, catechins (especially epigallocatechin gallate or EGCG), and caffeine. Several observational and experimental studies have reported associations between green tea consumption and reduced depressive symptoms. The most notable compound, L-theanine, is an amino acid that can cross the blood-brain barrier and is thought to promote relaxation without sedation, possibly by modulating neurotransmitters such as dopamine and serotonin. Some small-scale clinical trials and animal studies suggest that L-theanine and EGCG may exert antidepressant-like effects, likely through mechanisms involving neuroprotection, anti-inflammatory activity, and the regulation of the hypothalamic-pituitary-adrenal (HPA) axis.

Despite these findings, the evidence is still limited and mostly preliminary. Meta-analyses of observational studies have found a correlation between higher green tea intake and lower prevalence of depressive symptoms, but causation cannot be established from these studies. Randomized controlled trials (RCTs) are few, and those available generally involve small sample sizes and short durations. Additionally, the effects of green tea or its extracts appear modest compared to standard antidepressant medications. Therefore, while some scientific evidence suggests a potential benefit, it is not robust or conclusive, and green tea should not be considered a primary treatment for depression. Its use may be best viewed as a complementary approach within a broader mental health regimen.