L-Theanine for Cognitive Function

Research suggests that L-theanine may support several aspects of cognitive function, including attention, working memory, reaction time, and executive function, with the most consistent evidence coming from its use in combination with caffeine rather than as a standalone supplement. The evidence base includes randomized controlled trials, systematic reviews, meta-analyses, and preclinical animal studies, and the general direction is moderately positive, though findings are not uniform across all cognitive domains or populations. Studies indicate that while L-theanine crosses the blood-brain barrier, influences neurotransmitter activity, and demonstrates neuroprotective properties in animal models, human clinical trial data remain limited by small sample sizes, variability in study designs, and inconsistent outcomes, particularly for measures like simple reaction time and Stroop test performance. Several reviewers caution that the current evidence does not yet fully substantiate the broad cognitive enhancement claims commonly made for L-theanine as a supplement, and that more rigorous, large-scale human trials are needed before firm conclusions can be drawn.