The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.
Giesbrecht et al (2010) Nutr Neurosci. 13:283-90.
Study: The study investigated the effect of a combination of 97 mg L-theanine and 40 mg caffeine as compared to placebo treatment on cognitive performance, alertness, blood pressure, and heart rate in a sample of young adults (n = 44). Cognitive performance, self-reported mood, blood pressure, and heart rate were measured before L-theanine and caffeine administration (i.e. at baseline) and 20 min and 70 min thereafter.
Results: The combination of moderate levels of L-theanine and caffeine significantly improved accuracy during task switching and self-reported alertness (both P < 0.01) and reduced self-reported tiredness (P < 0.05).
Conclusion: 97 mg of L-theanine in combination with 40 mg of caffeine helps to focus attention during a demanding cognitive task.