L-theanine (200mg) with around 100-150mg of caffeine has an extremely noticeable, positive effect on my ability to focus, feeling of "well-situatedness", and overall calmness. L-theanine by itself doesn't seem to do much. Caffeine on its own wakes me but makes me feel jittery and anxious, so it's definitely an interaction effect. Taurine has a much smaller effect on calmness, sans interactions - often indistinguishable from any other mild focus exercise like box breathing or stretching.