Human studies have found that supplemental L-theanine can cross the blood-brain barrier and promotes the generation of alpha brain waves, suggesting a state of relaxation.
Controlled clinical trials have shown that L-theanine can support a healthy stress response by improving stress perception and resilience. The stress-buffering mechanisms of L-theanine have been connected to the ability of L-theanine to increase serotonin and dopamine production in the brain. L-theanine has also been shown to significantly increase alpha brain wave activity, which is critical for increasing attention as well as promoting a sense of relaxation.
In a study using 16 healthy volunteers, electroencephalograph (EEG) readings of participants were recorded following the ingestion of 50 mg of L-theanine. The researchers found a greater increase in alpha brain wave activity versus placebo. L-theanine has also been shown to have a protective effect for nerve cells and reduces excitatory glutamate activity in the brain.