"These results replicate previous evidence which suggests that L-theanine and caffeine in combination are beneficial for improving performance on cognitively demanding tasks." from “The combined effects of L-theanine and caffeine on cognitive performance and mood”, Nutritional Neuroscience

"The combination has shown improvement in short-term sustained attention and overall cognition." from "The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic Review", Research Update Organization

"We found an increase in hit rate and target discriminability (d#) for the combined treatment relative to placebo, and an increase in d# but not hit rate for caffeine alone, whereas no effects were detected for L-theanine alone." from “L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance”, The Journal of Nutrition

"L-theanine and caffeine increased self-reported alertness and decreased feelings of tiredness. Taken together with previous studies, these findings indicate that L-theanine in combination with caffeine may help to focus attention during cognitively demanding tasks." from “The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness”, Nutritional Neuroscience

"In addition to improving RVIP (Rapid Visual Information Processing) accuracy and ‘mental fatigue’ ratings, the combination also led to faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy. ‘Headache’ and ‘tired’ ratings were reduced and ‘alert’ ratings increased. There was also a significant positive caffeine × l-theanine interaction on delayed word recognition reaction time." from “The effects of l-theanine, caffeine and their combination on cognition and mood”, Biological Psychology

"After reviewing the studies, we found the combination shows favorable clinical significance in the domains of attention, memory, cognition, and hyperactivity. Overall, we conclude that the combination of L-theanine and caffeine is likely a safe and effective cognitive enhancer." from "The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic Review", Research Update Organization

"Our findings suggest that supplementation of 200–400 mg/day of L-Theanine may assist in the reduction of stress and anxiety in people exposed to stressful conditions." from “The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review”, Plant Foods for Human Nutrition

"The results showed that l-Theanine intake resulted in a reduction in the heart rate (HR) and salivary immunoglobulin A (s-IgA) responses to an acute stress task relative to the placebo control condition. Moreover, analyses of heart rate variability indicated that the reductions in HR and s-IgA were likely attributable to an attenuation of sympathetic nervous activation. Thus, it was suggested that the oral intake of l-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation." from “l-Theanine reduces psychological and physiological stress responses”, Biological Psychology