L-Theanine is an amino acid found in green tea and in some mushrooms. Though it has generally been studied for its anxiolytic, stress-relieving properties, it also has a number of other physiological and pharmacological benefits.
A Japanese study has suggested that the oral intake of l-theanine provides anti-stress benefits by inhibiting cortical neuron excitation. L-theanine allows for enhanced awareness and mental clarity without drowsiness or agitation.
Another study conducted by the University of Shizuoka discovered the following:
In human volunteers, α-waves were generated on the occipital and parietal regions of the brain surface within 40 min after the oral administration of theanine (50–200 mg), signifying relaxation without causing drowsiness.
L-theanine can be found in teas and mushrooms. But, supplements are now available as well.