In a four-week, randomized, placebo-controlled crossover trial of 30 healthy adults, three Pittsburgh Sleep Quality Index subscale scores (sleep latency, sleep disturbance, and use of sleep medication) improved significantly more with 200 mg/day L-theanine than with placebo. Total depression, anxiety and sleep-quality scores improved only within the L-theanine period itself, without reaching significance against placebo. The Trail Making Test (parts A and B) improved significantly within the placebo period alone over the four weeks, a within-period change not seen with L-theanine, but that comparison and every other cognitive test showed no significant difference directly between L-theanine and placebo. A post-hoc subgroup with lower baseline scores, half the sample, showed a significant verbal-fluency advantage for L-theanine. These mixed results do not establish a general anti-anxiety or cognitive-enhancement effect.[1]
- Small exploratory study with multiple outcomes; not evidence for treating a diagnosed psychiatric disorder.
- Two of seven authors were employees of Taiyo Kagaku Co., Ltd., which supplied both the active and placebo tablets, measured serum L-theanine concentrations, and performed the unblinding; this is a material funding/conflict-of-interest limitation.
- Multiple outcomes and a post-hoc median-split subgroup were tested without a stated multiplicity correction; some nominally significant between-group results (e.g., p = 0.0499) may reflect chance, and the between-group PSQI-subscale findings should be read with that caution.
- Passage-checked in full text; no qualified clinical review.
Inspection history
Clinical review: not reviewed by a qualified clinician.
· Prior batch record retained as unverified historical input pending fresh review.
· nootropic batch: reopened source(s) via NCBI E-utilities / PMC Open Access; materially revised after full-text inspection.