The amino acid derivative L-theanine, also known as Y-glutamylcthylamide, is found naturally almost exclusively in tea leaves. It is able to cross the blood-brain barrier and is considered to be psychoactive. Although it makes up as much as 2 percent of the dry weight of tea leaves, the amount generally ingested through drinking tea is minute. Higher doses have recently been investigated as a possible complement to conventional anxiety, stress, hypertension, depression, sleep disturbance and schizophrenia treatments. Research on the therapeutic potential of this compound is still in its infancy and cannot be considered conclusive. Talk to your doctor before taking L-theanine to assess how much may be appropriate for you in consideration with your medical history and other medications.
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Mechanism of Action
Even though L-theanine closely resembles the stimulant neurochemical glutamate, it does not appear that L-theanine affects glutamate pathways in the brain to any significant degree. Instead, L-theanine is believed to increase GABA levels and activity, which may be responsible for much of its anti-anxiety effects. GABA is the brain's own inhibitory neurotransmitter. Anxiolytic medications like Valium work by affecting GABA activity, as does L-theanine. Secondarily, L-theanine may moderate dopamine and serotonin levels in the brain, although it is yet to be determined which regions of the brain experience increases or decreases in the levels of these neurotransmitters.
Research on Anxiety
In 2010, Dr. Michael Ritsner of the Technion–Israel Institute of Technology published an article in the "Journal of Clinical Psychiatry" that concluded that when 400 mg of L-theanine was added to an existing pharmacotherapeutic regimen, it produced a statistically significant reduction in the symptoms of anxiety. In a less rigorous study from "Biological Psychology" in 2007, Dr. Kiriya Kimura of Nagoya University found that L-theanine supplementation resulted in a reduction of heart rate and levels of stress-indicating hormones. The authors concluded that L-theanine should be the subject of further research as a potential treatment for anxiety. However, Kimura later concluded that neither L-theanine nor a benzodiazepine anti-anxiety medication was demonstrably effective in the treatment of induced anxiety symptoms.
Drug Interactions and Contraindications
L-theanine is not known to interact with any over-the-counter or prescription drugs. It is possible to speculate that L-theanine may increase the effects of other anxiolytics, sedatives or alcohol. Side effects other than headache are rare and include dizziness or gastrointestinal upset.
Safety and Dosage Considerations
Although the FDA has reaffirmed their classification of supplements containing L-theanine as "generally recognized as safe," it is important to remember that the doses in many nutritional supplements far exceed the 20 mg generally considered to be safe. An animal study published in 2006 by "Food Chemistry and Toxicology" found no adverse effects on behavior, food consumption, body weight, clinical chemistry, hematology, urinalysis, morbidity or mortality in a study population administered large amounts of L-theanine over 13 weeks. According to Drugs.com, the lethal dose is so high it is effectively impossible to achieve through normal therapeutic use of this compound. In a monograph published by "Alternative Medicine Reviews" in 2010, the publication recommends taking 200 mg twice or three times daily to treat anxiety. Nonetheless, longitudinal human studies are needed to determine the long-term safety of high dose L-theanine therapy. Consult your physician before using any new supplements.