Theanine may sharpen accuracy only when caffeine is in the mix
In one trial, 100mg of theanine with 50mg of caffeine had people spotting targets more accurately than placebo, on one brief task. Theanine by itself moved nothing.
What the study found
With caffeine, theanine sharpened accuracy; alone it did nothing
In one trial, 50mg of caffeine with 100mg of L-theanine had people spotting targets more accurately than on placebo. Caffeine alone improved a different measure, how well targets were told apart; theanine alone moved nothing. On this task, theanine only showed up with caffeine in the mix.
The caveat · Accuracy was one of several measures
The trial was built as a caffeine comparison, so the pairing was never its main question. Accuracy was one of several measures taken in that task. The advantage was over placebo, and caffeine alone was credited on a different measure, so nothing here sets the pair against caffeine by itself.
What we don't know
What this trial cannot show is whether the pair beats caffeine alone: its edge was over placebo, on one brief task. The edge is unconfirmed rather than contradicted.