L-theanine is an amino acid naturally found in tea. It has been shown to have a calming effect on the brain, triggering the production of alpha brain waves associated with wakefulness and relaxation, and decreasing beta brain waves associated with feelings of restlessness and nervousness. L-theanine influences the levels of the neurotransmitters dopamine, serotonin, norepinephrine, and glutamate, and is also metabolized into gamma-aminobutyric acid (GABA), a neurotransmitter that plays a key role in relaxation and memory.
L-theanine may help temporarily promote relaxation and improve feelings of stress. In one study, a group of 50 women aged 18 to 22 were divided into two groups: a high-anxiety group and a low-anxiety group. They were given either water (as a control) or a solution containing 50 mg or 200 mg of L-theanine, and their brain waves were measured for 60 minutes. Compared to the controls, the group receiving 200 mg of L-theanine showed a significant increase in alpha brain waves, indicating a relaxation effect. Similar results were observed in another clinical trial where 35 healthy young volunteers were given 50 mg of L-theanine and showed elevated alpha brain wave activity for the next 105 minutes.