A theanine drink may blunt cortisol's rise under stress, in one trial
Three hours after a drink with 200 mg of theanine, a stressful task did not raise the typical person's cortisol; after placebo it did. Resting cortisol was not compared.
What the study found
Cortisol's stress rise was blunted; resting levels were not compared
In one trial, healthy adults did a stressful task three hours after a drink carrying 200 mg of L-theanine, and on another day after placebo. After placebo the typical person's cortisol rose through the task; after the drink it did not. Cortisol at rest was never compared between the two.
The caveat · Four lost for too little saliva
Thirty-six people enrolled and 34 finished, but the effects were computed on 26, chosen after testing and before unblinding for having reacted to the task at baseline. Four people gave too little saliva and were left out of the cortisol analysis, and the paper does not say how many remained. The drink was not theanine alone: it also carried 25 mg of alpha-glycerylphosphorylcholine, 1 mg of phosphatidylserine and 10 mg of chamomile. Before dosing and at one hour the task did not reliably raise cortisol, so the rise the drink blunted appeared at one session out of three. A grant from a company, Neurobrands, paid for the trial, and the paper says the funder had no input into its design, conduct or interpretation.