L-theanine is a non-essential amino acid that occurs primarily in leaves of the plant Camellia sinensis, which is used to produce black, oolong and green tea. A synthetic form of L-theanine also is available as a supplement and food additive called Suntheanine. Preliminary research results show promise for a few benefits.
People have used L-theanine and green tea historically as a way to reduce stress while remaining alert and avoiding drowsiness. A study published in the January 2007 issue of "Biological Psychology" found that L-theanine intake resulted in reduced heart rate and salivary responses to a stressful task when compared with a placebo. Drugs.com cites a Japanese study showing that L-theanine promotes alpha brain waves, an indicator of alert relaxation. Based on this study, Drugs.com notes that a dosage of 50mg to 200mg may provide a relaxation effect.
Resistance to Illness
Laboratory and animal tests indicate L-theanine may promote natural resistance to tumors and to microbial infections, according to Drugs.com. A study published in "Bioscience, Biotechnology and Biochemistry" in April 2002, for instance, found that dietary powdered green tea and theanine administered to rats had beneficial effects against induced liver cancer in these animals.
Some companies producing skin care products are beginning to include L-theanine in their cosmetics. Dermascriptives, for instance, includes L-Theanine in a night cream to moisturize and provide nourishment to stressed skin.