L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance.
S.P. Kelly, M. Gomez-Ramirez, J.L. Montesi, J.J. Foxe
 The combined effects of L-theanine and caffeine on cognitive performance and mood.
G.N. Owen, H. Parnell, E. A. De Bruin, J. A. Rycroft
 The effects of L-theanine, caffeine and their combination on cognition and mood.
C.F. Haskell, D.O. Kennedy, A.L. Milne AL, K.A. Wesnes, A.B. Scholey