The study and its comparison
Thirty adults received 200 milligrams daily of theanine and placebo in separate four-week periods. Mood, sleep and cognitive scores were assessed in a randomized double-blind crossover design. [1]
Some mood and cognitive scores improved within the theanine period. Between-treatment differences favored theanine for selected sleep subscales, while a verbal-fluency finding arose in a lower-scoring subgroup. [1]
What the finding establishes
Within-period changes and subgroup findings are not equivalent to an overall treatment effect. Four weeks also cannot establish indefinite safety. Taiyo Kagaku funded the study and supplied tablets; two authors were company employees. These disclosures should accompany interpretation rather than be hidden behind a general wellness claim. [1]
A hypothetical distinction
Imagine a trial follows people for one month. An uneventful month does not measure what happens after several years.
| Detail | Interpretation |
|---|---|
| Measured outcome | Keep the endpoint specific |
| Study preparation | Not every retail product |
| Remaining uncertainty | Not resolved by a mechanism |
Sources for this article
- Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial - PMC
Source consulted: 2026-09-19. This is a reference resource, not a claim that we conducted the studies or tested a product.