Dietary supplements containing L-theanine are promoted for their ability to promote relaxation, reduce stress, and improve sleep, as well as boost concentration and alertness. Can it really fine-tune your mind?
An amino acid found primarily in black and green tea, L-theanine is partly responsible for the beverage’s impact on mood. It appears to alter levels of various neurotransmitters, producing a calming effect that helps counter the stimulating action of the caffeine in tea. At the same time, it works with the caffeine to promote concentration on mental tasks, producing what tea lovers sometimes call “alert calmness.”
Largely because of these effects associated with tea, L-theanine is marketed as a dietary supplement—on its own and as an ingredient in many formulas promoted for relaxation and stress reduction. It is also used at lower levels as an additive in foods and beverages, especially in Japan, usually to provide a savory flavor.
Teasing apart theanine’s effects
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 findings have been inconsistent. And a few studies suggest detrimental effects—on cognitive test performance, for instance.
Bottom line: L-theanine has interesting potential psychoactive properties, but the research so far has been inadequate to support the marketing claims. Its effects may be unpredictable, especially when it is combined with other ingredients (as it is in many supplements) or when taken with various medications. Consumers may become habituated to the compound’s effects over time. Moreover, some supplements apparently contain mostly D-theanine, a slightly different form that may not have L-theanine’s neurochemical actions. Appropriate dosing and long-term safety of L-theanine supplements are unknown.
Until there’s better evidence, we advise drinking tea rather than taking the supplements. The pleasurable effects produced by the synergy of L-theanine, caffeine, and other compounds naturally in tea have stood the test of time.