“L-Theanine and Caffeine Improve Task Switching but Not Intersensory Attention or Subjective Alertness”, 2010-04-01 (; backlinks; similar):
Tea ingredients l-theanine and caffeine have repeatedly been shown to deliver unique cognitive benefits when consumed in combination.
The current randomized, placebo-controlled, double-blind, cross-over study compared a combination of l-theanine (97 mg) and caffeine (40 mg) to a placebo on 2 attention tasks and a self-report questionnaire before, and 10 and 60 min after consumption.
The combination of l-theanine and caffeine statistically-significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved statistically-significantly.
The results support previous evidence that l-theanine and caffeine in combination can improve attention.