Camellia sinensis (L.) Kuntze · supplement
Evidence tier: limited
Promotes calm, focused alertness without drowsiness
Acts on the nervous system. It crosses the blood brain barrier and is associated with increased alpha brain wave activity, a pattern linked to relaxed alertness, and it modulates GABA, dopamine and serotonin and binds weakly at glutamate receptors. A single dose crossover trial showed it raises frontal alpha power and lowers salivary cortisol after an acute stressor (PMID 34562208). Note EFSA called the attention mechanism speculative.
Modest at best. The regulatory counterweight is the decisive fact: EFSA has TWICE found the isolated theanine evidence insufficient. In 2011 it concluded no cause and effect relationship was established between L-theanine and improvement of cognitive function, alleviation of psychological stress, maintenance of normal sleep, or reduction of menstrual discomfort, so all four are non authorised claims in the EU (EFSA Journal 2011;9(6):2238). In 2018, assessing black tea and attention, EFSA stated 'no evidence was provided on the effects of l-theanine on attention', called the proposed mechanism 'speculative', and found that studies of caffeine plus l-theanine versus caffeine alone 'do not show an effect... separate to that of caffeine alone'; EFSA accepted that black tea improves attention but attributed it to CAFFEINE (EFSA Journal 2018;16(5):e05266). Against that, recent trials are encouraging for acute attention: a 2026 meta analysis of 31 randomised trials (1168 people) found a single 200 mg dose improved choice reaction time (SMD 0.51) and concluded 'L theanine is safe and shows a robust short term benefit on attention in healthy adults' (PMID 42410082). The clearest cognitive benefit belongs to the CAFFEINE PARTNERSHIP, not to theanine alone (PMID 40314930). Stress and sleep effects are small and mostly subjective. Genuinely low risk, so the danger with this ingredient is overclaiming benefit, not underclaiming harm.
200 mg as a single dose for acute attention, and about 200 to 400 mg per day for stress or sleep use. The most studied caffeine pairing is roughly 97 mg theanine with 40 mg caffeine, or 200 mg theanine with higher caffeine doses.
Morning or whenever focus and calm are needed. Works within 30 to 60 minutes.
Onset: ~1 days
Generally very safe with a strong tolerability profile. Limited formal safety data in pregnancy and lactation; use with caution. Synergistic calming effect when combined with caffeine without sedation.
Pregnancy: caution
Breastfeeding: caution
Active compounds: L-theanine (N-ethyl-L-glutamine, gamma-glutamylethylamide)
Remedies using L-Theanine · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.