L-theanine is an amino acid found in green and black tea. Studies show that, even with 50mg doses mimicking normal dietary behaviour, theanine increases production of alpha brain waves, which are the brain waves that increase creativity and decrease depression.

Theanine is a glutamate antagonist, meaning it blocks glutamate receptors in the brain, which is part of the reason some people report a calming effect after taking theanine. Theanine has also shown promise as a sleep aid and in stopping the release of histamine from mast cells.

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.

L-theanine promotes relaxation and facilitates sleep by contributing to a number of changes in the brain:

Boosts levels of GABA and other calming brain chemicals. L-theanine elevates levels of GABA, as well as serotonin and dopamine. These chemicals are known as neurotransmitters, and they work in the brain to regulate emotions, mood, concentration, alertness, and sleep, as well as appetite, energy, and other cognitive skills. Increasing levels of these calming brain chemicals promotes relaxation and can help with sleep.
Lowers levels of “excitatory” brain chemicals. At the same time it is increasing chemicals that promote feelings of calm, L-theanine also reduces levels of chemicals in the brain that are linked to stress and anxiety. This may also be a way that L-theanine can protect brain cells against stress and age-related damage.
Enhances alpha brain waves. Alpha brain waves are associated with a state of “wakeful relaxation.” That’s the state of mind you experience when meditating, being creative, or letting your mind wander in daydreaming. Alpha waves are also present during REM sleep. L-theanine appears to trigger the release of alpha-waves, which enhances relaxation, focus, and creativity. One of the appealing aspects of L-theanine is that it works to relax without sedating. That can make L-theanine a good choice for people who are looking to enhance their “wakeful relaxation,” without worrying about becoming sleepy and fatigued during the day.