Caffeine and L-theanine
L-theanine is known for its synergistic combination with caffeine. This combination is naturally found in teas but maybe not in the desired doses or ratio. Black teas are usually higher in caffeine whereas matcha green teas are relatively higher in theanine. Theanine has shown the potential to diminish the negative aspects of caffeine while simultaneously sharing some of the positive aspects like increased attention.[1, 2]
Research has shown that L-theanine reduces the jitters that many people experience from consuming too much caffeine.
Downsides of combing L-theanine with Caffeine
You may get an upset stomach or nausea when combining l-theanine with caffeine.
Furthermore, some users don't like combining L-theanine with caffeine because it may reduce the rush from caffeine. However, if you want to reduce anxiety and increase your calmness, L-theanine to your daily
-  Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., & Scholey, A. B. (2008). The effects of l-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 77(2), 113–122.
-  Parnell, H., Owen, G., & Rycroft, J. (2006). Combined effects of L-theanine and caffeine on cognition and mood. Appetite, 47(2), 273.