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★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.
Taking 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.
What the study found
Theanine blunted caffeine's blood-pressure rise, in one trial
Taken together with 250mg of caffeine, 200mg of L-theanine flattened the blood-pressure rise the caffeine produced, in 48 people. Theanine on its own changed nothing about alertness, jitteriness or mood; those all came from the caffeine.
The caveat · Built around caffeine, not theanine
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.