L-Theanine is a relaxing and nondietary amino acid found pretty much exclusively in teas from Camellia sinensis (alongside green tea catechins and caffeine) and is known to promote relaxation without sedation. It appears to be effective at this as well as reducing stress at standard dosages. L-theanine was discovered as a constituent of green tea in 1949 and was approved in Japan in 1964 for unlimited use in all foods, including chocolates, soft drinks, and herb teas, except infant foods. It also provides a unique umami (brothy or savory) taste and flavor to green tea infusion. L-theanine may help relieve stress by inducing a relaxing effect without drowsiness and may also possess immunologic attributes. Theanine may also have effects on the cardiovascular system and play a preventative role in cancer; however, limited clinical information is available to support these claims. L-Theanine and its positive effects on cognitive performance is one of its most important functions. Because of chemical structure of L-Theanine similar to glutamate it can act as a neurotransmitter related to memory. In a study made on rats, it was found out that L-Theanine modulated the serotonin and dopamine levels and increased learning skills with memory. In addition, it is stated that L-Theanine increases neuro - throphine mRNA level by activating its neuro - transmitter inhibiting system and supports the central nervous system that helps the development of brain functions. L-Theanine had a positive effect on memory and had positive effects on the treatment and prevention of Alzheimer. Theanine is an antagonist of the NMDA receptors (albeit with fairly weak efficacy) and can inhibit synaptic release of glutamate via blocking the transporter competitively. Theanine may also reduce glutamate levels, but this is also a fairly weak mechanism requiring a high concentration of theanine.