ʟ-Theanine is the amino acid critical for its calming influence on cognitive function. It crosses the blood-brain barrier to help establish a state of relaxation while maintaining alertness. Upon exposure to the brain, it stimulates production of gamma-aminobutyric acid (GABA), the chemical produced by the brain that blocks excitatory stimuli that contribute to stress.

Studies have also shown ʟ-theanine to encourage alpha wave activity associated with a state of serenity and mental clarity.