L-theanine is an amino acid found naturally in tea. It has been shown to exert a calming effect on the brain, triggering the production of alpha brain waves associated with an awake-relaxed state, and decreasing beta brain waves associated with feelings of restlessness and nervousness. L-theanine influences levels of the neurotransmitters dopamine, serotonin, norepinephrine, and glutamate and is also metabolized into gamma-aminobutyric acid (GABA), a neurotransmitter that is key to relaxation and memory.
L-theanine can help temporarily promote relaxation and improve feelings of stress. In one study, a group of 50 female subjects, aged 18–22 years, were divided into a high-anxiety and a low-anxiety group. They received 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 afterwards. Compared to controls, the group receiving 200 mg of L-theanine had a significant increase in alpha brain waves, indicating a relaxation effect. Similar results were seen in another clinical trial where 35 healthy young volunteers received 50 mg of L-theanine and had elevated alpha brain wave activity for 105 minutes afterwards.