L-theanine for Concentration

L-theanine (often referred to as theanine) is relaxing and also enhances concentration.
It is the main reason why tea is relaxing and relieves stress, unlike coffee, even though both contain caffeine. 

Japanese green tea contains high amounts of L-theanine- a natural amino acid found in green tea—mainly evergreen shade-grown green teas such as gyokuro and matcha.

Consuming green tea can reduce stress and anxiety and boost mental health and performance by inducing a state of relaxed awareness.

L-theanine reduces heart rate, blood pressure, cortisol, and feelings of stress and anxiety.