Theanine enters the brain by passing through blood-brain barrier. Once it is in the brain, Theanine causes significant increases in serotonin and/or dopamine concentrations in the brain, especially in striatum, hypothalamus, and hippocampus.[13], [14] Serotonin and dopamine are often referred to as the brain's "feel good chemicals." The body naturally produces more of these chemicals when we are happy or feeling good. When serotonin and dopamine concentrations are increased, the individual feels more relaxed and calmer.