L-theanine is a non-protein amino acid, derived from L-glutamic acid, commonly found in the plant Camellia sinensis and contains bioactive substances, vitamins, minerals and antioxidants. This amino acid can be obtained by chemical synthesis or tea isolation. It was commercially developed due to its promising effects of promoting relaxation and feeling of well-being. In oral administration, L-theanine is absorbed through the intestinal tract and, soon a large amount in the blood flows to the brain through the blood-brain barrier. Theanine (C₇H₁₄N₂O₃) is metabolised in the kidneys to glutamic acid and ethylamine. Its main targets are glutamate, gamma-aminobutyric acid (GABA), dopamine and serotonin, impacting to a certain extent on neurochemical levels. According to studies, after 15 minutes of oral administration of 200mg, brain activity is influenced by the stimulation of alpha wave production. This form of administration can help anxious people to concentrate in their daily tasks and the continuous intake can increase brain levels of dopamine and GABA, explaining the feeling of relaxation. The action of L-theanine also suggests that it may cause a modulation of the effects of caffeine and thereby lower cortisol levels. This review intends to analyze the effects of L-theanine and its interaction with the central nervous system, relating it to anxiolytic effects and decrease of stress levels, in order to confirm a pattern of change between physiological indices after ingestion.