L-theanine, a natural constituent in tea, and its effect on mental state
Key Finding
L-theanine promotes relaxation and improves attention when combined with caffeine, without causing drowsiness.
Plain-English Summary
This systematic review examined the cognitive and mental effects of L-theanine, an amino acid found naturally in tea leaves. The researchers analyzed multiple controlled studies investigating L-theanine both alone and in combination with caffeine.
The review found that L-theanine promotes relaxation without drowsiness, as evidenced by increased alpha brain wave activity. When combined with caffeine, L-theanine improved both speed and accuracy of performance on attention-switching tasks and reduced susceptibility to distracting information.
The synergistic effects of L-theanine and caffeine were particularly notable, with the combination producing more pronounced improvements in cognitive performance than either compound alone. These effects typically occurred at doses of 50-100mg L-theanine combined with 50-100mg caffeine.