The amino acid L-theanine could have a positive effect on your anxiety and mood. Some research suggests L-theanine decreases anxiety and improves cognition, but its effect on anxiety is not yet fully understood. According to Memorial Sloan-Kettering Cancer Center, L-theanine appears to affect dopamine, serotonin and other neurotransmitters in rats, but no clinical trials have been conducted to conclusively determine its effect on humans.
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Green tea contains L-theanine, and tea drinkers often credit the beverage’s L-theanine content for inducing relaxed feelings and peace of mind. L-theanine is also sold as a nutritional supplement. Some energy drink manufacturers add the amino acid to their products as well.
L-theanine alters rats’ brain chemistry, but studies have drawn different conclusions about the implications of this research. A study published in Neurochemical Research found that L-theanine crossed the blood-brain barrier in rats. Their levels of norephinephrine, a stimulating neurotransmitter, did not increase, but their levels of serotonin, a neurotransmitter that regulates anxiety and depression, rose. Another study published the same year, however, found L-theanine decreased serotonin levels when administered to rodents.
A 2004 study published in Human Psychopharmacology found that administering 200 mg of L-theanine to human subjects made them feel more relaxed under “resting conditions.” The study only included 16 volunteers, far fewer than most large-scale, reputable clinical trials. In another study, UK researchers determined subjects were better able to perform mentally challenging problems when given a combination of L-theanine and caffeine rather than caffeine alone.
Some evidence shows that L-theanine may decrease anxiety by increasing alpha waves in the brain. Some researchers theorize these electromagnetic waves slow the mind. In one Netherlands study, participants given 50mg of L-theanine showed an increase in alpha waves as measured by an electroencephalograph (EEG). A very small Japanese study produced similar results.
The Food and Drug Administration classifies L-theanine supplements as "Generally Recognized as Safe" in dosages up to 250mg. Nevertheless, Sloan-Kettering suggests L-theanine could interact with sedatives, chemotherapy and cholesterol-lowering medications. If you take any of these drugs, check with your physician before consuming any L-theanine supplement.