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Myth check

In a caffeine and theanine blend, the calm focus is the caffeine

Across 11 pooled trials, alertness tracked the caffeine more closely than the theanine. In one trial of 48 people, theanine flattened caffeine's blood-pressure rise but left jitters and mood alone.

CaffeineL-theanine

Caffeine and theanine are sold together as a smart stack, theanine smoothing the edges. Across eleven pooled trials, the gain in alertness over the first two hours tracked the caffeine in the mix more than the theanine. In 48 people, theanine alone moved neither jitters nor mood, and the one thing it changed was caffeine's blood-pressure rise. Two trials at matching doses disagree on whether the pair beats either alone. The calm is caffeine's; theanine's quieter work is on blood pressure.

The findings behind this

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Mental & cognitiveYour alertness responds to the caffeine in a blend, not the theanine

Pooling 11 trials of caffeine-theanine blends, the gain in alertness over the first two hours tracked how much caffeine was in the mix more closely than how much theanine.

★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.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.Click to keep this openFocus and think clearlyL-theanine
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Physical & bodyTaking theanine with caffeine may soften the blood-pressure spike

In one trial of 48 people, 200mg of theanine taken with 250mg of caffeine flattened the blood-pressure rise the caffeine caused. On its own, theanine left alertness, jitters and mood unchanged.

★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.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.Click to keep this openSupport heart and blood flowL-theanine
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Mental & cognitiveCaffeine and theanine each kept attention up; together, no extra gain

In one trial, 27 people did a two-hour attention task. 50mg of caffeine or 100mg of theanine on its own held errors down against placebo, and the two together did no better than either alone.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.Conflicting evidenceA 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.Click to keep this openFocus and think clearlyL-theanine
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Mental & cognitiveTheanine 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.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.Conflicting evidenceThe 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.Click to keep this openFocus and think clearlyL-theanine
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SleepWith a little theanine, a small caffeine dose may not cost you sleep

In one small trial of young women, 30mg of caffeine kept them awake longer after they first fell asleep; 50mg of theanine taken with it brought that wake time back to placebo.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.CautionOne 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.Click to keep this openSleep betterL-theanine

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