Most research on the basic actions of L-theanine has been done in animals. Some preliminary human studies, typically using doses of L-theanine about 10 to 20 times higher than that in a cup of tea, have suggested possible benefits, such as the following:
In a Japanese study in the Journal of Physiological Anthropology, college students who took L-theanine experienced less anxiety and had smaller increases in blood pressure when under psychological or physical stress than when they took a placebo. Similarly, another Japanese study in Pharmacology, Biochemistry, and Behavior found that graduate students who took L-theanine experienced less anxiety (as measured by a questionnaire and by a salivary marker for stress) when they were assigned stressful work in a pharmacy, compared to a placebo.
In a Canadian study in Alternative Medicine Review, L-theanine improved some aspects of sleep quality in boys with attention-deficit hyperactivity disorder (ADHD).
In a preliminary Israeli study in the Journal of Clinical Psychiatry, L-theanine helped relieve anxiety symptoms and augment antipsychotic treatment in patients (ages 19 to 55) with schizophrenia.
But most of the studies have been small and short-term, and almost all were limited to children or young adults. Many have had methodological weaknesses, and the find