“L-theanine reduces stress and anxiety.”
L-theanine has at most a small, short-term effect on stress, and it has not been shown to reduce anxiety.
L-theanine is not a proven treatment for stress or anxiety. Any calming effect seen in studies was small and showed up mostly right after a single dose.
If stress or worry is getting in the way of daily life, talk with a doctor or mental health professional rather than relying on L-theanine.
Talk to a healthcare professional if: stress or worry is getting in the way of sleep, work or relationships, or you take prescribed medicine for anxiety or depression and are thinking of switching to a supplement.
A 2026 review of 31 trials found only a small drop in short-term stress, mostly driven by lower-quality studies, and no consistent effect on anxiety. Confidence is Limited because the trials were small, short and mixed in dose, people and measures.
L-theanine has at most a small, short-term effect on stress, and it has not been shown to reduce anxiety. In a 2026 review of 31 trials (1,168 people), a single dose lowered stress only slightly, and that result leaned on studies at high risk of bias.
Anxiety results in the 2026 review were inconsistent and not significant, except in one small study of people with anxiety linked to psychosis who took 400 mg a day for 8 weeks. The same review found a single 200 mg dose sped up reaction times a little, and a possible short-term lift in mood in healthy people that still needs testing in better trials. No serious side effects were reported. A 2025 review of tea, theanine and theanine with caffeine in healthy people found no trial at low risk of bias; it was funded in part by a tea company.
- Gerolymos C, Saddier E, Boyer L, Fond G. Cognitive and affective effects of L-theanine: a systematic review and meta-analysis of 31 randomized trials. Molecular Psychiatry. 2026;31(11):6592-6602. DOI: 10.1038/s41380-026-03727-9. PMID: 42410082
- Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B. Effects of tea (Camellia sinensis) or its bioactive compounds l-theanine or l-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews. 2025;83(10):1873-1891. DOI: 10.1093/nutrit/nuaf054. PMID: 40314930. PMCID: PMC12422004