One 200mg dose of theanine eased stress within an hour, cortisol later
In one trial of 26 adults, a drink carrying 200mg of theanine and three minor ingredients cut rated stress at one hour, not at three; cortisol fell at three hours, not at one.
What the study found
Rated stress eased at one hour and cortisol at three, not together
In one trial of 26 healthy adults, the drink was not theanine alone: 200mg of L-theanine plus small doses of three other ingredients. Rated stress fell against placebo at one hour, and by three hours the arms matched. Cortisol ran the other way: no difference at one hour, lower at three.
The caveat · The 26 were picked after the fact
Thirty-four people finished the trial, but the treatment effects were computed on 26 — the ones who had actually reacted to the task at baseline, picked out after the fact. An industry grant funded the study, and the paper says the funder had no hand in the analysis. The other ingredients were phosphatidylserine, alpha-glycerylphosphorylcholine and chamomile, each in a small dose. Why the two effects arrived two hours apart is unexplained. Performance on the task itself never moved.