L-theanine

The 11 trials used a spread of doses and designs rather than one fixed ratio, so this is a pattern across mixtures rather than a test of any single blend. The authors call theanine's contribution comparatively modest rather than absent, which leaves room for a larger pool to move it. And every trial pooled here tested combinations, so none of it measures theanine by itself.

One trial of 48 people, and it was designed to study caffeine, with theanine as the modifier rather than the subject. For anyone taking theanine by itself for calm focus, the same trial is a null result: alertness, jitteriness and mood did not move.

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.

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.

This was whole matcha, theanine and catechins and caffeine together, so no result here belongs to theanine specifically. The two results that moved were secondary outcomes, which carry less weight than the ones the trial was built to test. And everyone in it already had cognitive decline, which is not a healthy adult drinking green tea.

Every outcome here is what people reported about their own sleep; nothing was recorded by a wrist monitor or in a sleep lab. Few of the pooled trials tested theanine on its own rather than mixed with other ingredients, so its individual share stays blurred. And the authors say the best dose and duration are still undetermined.

Twenty-six of the 34 who finished were analysed, and they were the ones who had reacted to the task at baseline. The drink was not theanine alone: phosphatidylserine, alpha-glycerylphosphorylcholine and chamomile came with it, in small doses. An industry grant funded the trial, and the paper says the funder had no hand in its design or analysis. A brain-wave finding in the same trial turned up only in the more anxious participants and did not track the stress or cortisol results, so it stands unexplained.

This measured the tea itself, not a brewed cup, so what reaches a drink is a separate question. It is a chemistry survey, so it says nothing about what any of it does in a person.

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 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.

A single two-hour task. Theanine's effect showed up in behaviour but not in the brain-wave marker much of this field leans on, so the two kinds of evidence do not line up here. And it disagrees with a similarly dosed trial that did find an advantage for the combination.

What is open is whether pairing theanine with caffeine helps attention generally or only on the brief task that found it. Counting errors over two hours in 27 people, the pair did no better than either alone.

The participants skewed middle-aged and older, and most were women. A long list of outcomes was tested at once, which on its own makes some of the positive ones likely to be chance.

One small crossover trial in young women only, so nothing here covers men, older adults or anyone especially sensitive to caffeine. The 30mg of caffeine is well under a standard cup of coffee at roughly 95mg, which leaves the everyday dose untested. The lead author is affiliated with a commercial tea company.

This is electrical activity recorded in one small single-lab study, not behaviour and not how focused anyone felt or performed. A distinct signature is not the same thing as better concentration.