Compounds in Green Tea Can Improve Brain Function–One of the key active ingredient in green tea is caffeine, which is a well-known stimulant. However, this beverage does not contain as much caffeine as coffee does. Nonetheless, green tea does have enough caffeine to help keep you alert and focused. Caffeine acts as a binding agent and blocks an inhibitory hormone in the brain called Adenosine. As a result, there is an increase in the concentration of neurotransmitters, such as norepinephrine and dopamine, as well as the firing of neurons. Moreover, caffeine has also been linked to improved mood, reaction time, memory, and vigilance