The effects of l-theanine, caffeine and their combination on cognition and mood

l-Theanine is an amino acid found naturally in tea. Despite the common consumption of l-theanine, predominantly in combination with caffeine in the form of tea, only one study to date has examined the cognitive effects of this substance alone, and none have examined its effects when combined with caffeine. The present randomised, placebo-controlled, double-blind, balanced crossover study investigated the acute cognitive and mood effects of l-theanine (250 mg), and caffeine (150 mg), in isolation and in combination. Salivary caffeine levels were co-monitored. l-Theanine increased ‘headache’ ratings and decreased correct serial seven subtractions. Caffeine led to faster digit vigilance reaction time, improved Rapid Visual Information Processing (RVIP) accuracy and attenuated increases in self-reported ‘mental fatigue’. In addition to improving RVIP 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. These results suggest that beverages containing l-theanine and caffeine may have a different pharmacological profile to those containing caffeine alone.