L-Theanine Clinical Evidence

Nobre AC, Rao A, and Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. 2008;17 Suppl 1:167-8.

Topic:
What effect does L-Theanine, at realistic dietary doses, have on mental alertness and arousal?

Background
L-Theanine, present in tea, has been shown to increase alpha- waves in the brain. This means it creates a state of relaxation without causing drowsiness. However, this effect has only been proven at high doses. What effect does L-theanine have at a lower dose (equivalent to 2.5 cups of black tea)?

Study Type:
Human clinical intervention trial

Study Design:
Placebo-controlled. Subjects’ EEGs were measured at baseline and in fifteen-minute intervals from 45 to 105 minutes after ingesting either L-Theanine or placebo. Subjects were either resting with eyes closed or engaged in a passive activity while the EEGs were taken.

Subjects:
35 healthy young subjects

Dosage:
A single dose of 50 mg

Results:
There was a greater increase in alpha wave activity in the treatment group than in the control group. This was true both for resting subjects and those performing the activity.

Conclusion:
“These data indicate that L-theanine, at realistic dietary levels, has a significant effect on the general state of mental alertness or arousal.”

Ritsner MS, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. 2011 Jan;72(1):34-42.

Topic:
Can L-theanine reduce anxiety in patients with schizophrenia and schizoaffective disorder?

Background:
People with schizophrenia and schizoaffective disorder often suffer from anxiety. Can L-theanine, a component of tea with known relaxing properties, help?

Study Type:
Human clinical intervention trial

Study Design:
Double-blind, randomized, placebo-controlled. 40 participants with schizophrenia or schizoaffective disorder took L-theanine or a placebo along with their antipsychotic medications. Researchers measured their mood with the Positive and Negative Syndrome Scale (PANSS), the Hamilton Anxiety Rating Scale (HARS), and the Cambridge Neuropsychological Test Automated Battery (CANTAB). They also noted any side effects.

Dosage:
400 mg/day L-theanine, taken with antipsychotic medications, for 8 weeks

Participants:
60 patients diagnosed with schizophrenia or schizoaffective disorder (40 completed the study).

Results:
Compared to placebo, L-theanine significantly reduced anxiety on HARS and increased positive scores on the PANSS. L-theanine was safe and well-tolerated.

Conclusion:
“L-theanine augmentation of antipsychotic therapy can ameliorate positive, activation, and anxiety symptoms in schizophrenia and schizoaffective disorder patients. Further long-term studies of L-theanine are needed to substantiate the clinically significant benefits of L-theanine augmentation.”

Nathan, PJ, et al. The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. 2006;6(2):21-30.

Topic:
What are the mechanisms behind L-theanine’s actions in the brain?

Background:
L-theanine is a relaxing agent found in tea. How does it work?

Study Type:
Review

Summary:
Animal research suggests L-theanine:

•  Increases brain serotonin, dopamine, and GABA
• Has affinity for AMPA, Kainate, and NMDA receptors
• May have neuroprotective effects through antagonistic effects on group 1 metabotropic glutamate receptors 
• May improve learning and memory

Conclusions:
“Overall, L-theanine displays a neuropharmacology suggestive of a possible neuroprotective and cognitive enhancing agent and warrants further investigation in animals and humans.”

Kimura K, et al. L-Theanine reduces psychological and physiological stress responses. 2007 Jan;74(1):39-45.

Topic:
Can L-Theanine reduce psychological and physiological stress?

Background:
L-Theanine is an amino acid present in green tea that has been
shown to block L-glutamic acid from binding to glutamate
receptors in the brain. This action suggests it may be able to
influence psychological and physiological reactions under
stress conditions.

Study Type:
Human clinical intervention trial

Study Design:
Double-blind, placebo-controlled. Subjects were given a mental
arithmetic task to perform, which acted as a short-term
stressor. All subjects at different times took L-Theanine before
beginning the task, took L-Theanine during the task, took a
placebo and took nothing.

Subjects:
12 Subjects 

Results:
When subjects took L-Theanine, their heart rates and salivary
immunoglobulin A (s-IgA) responses to the stress task were
reduced compared to when they took placebo. Reductions in
both heart rate and s-IgA were probably caused by decreased
activation of the sympathetic nervous system.

Conclusion:
“[I]t was suggested that the oral intake of L-Theanine could
cause anti-stress effects via the inhibition of cortical neuron
excitation.”

Lu K, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. 2004 Oct;19(7):457-65.

Topic:
How does L-theanine affect relaxation in different mood states?

Background:
L-theanine has traditionally been used as a relaxing agent. How does it compare to a benzodiazepine medication (alprazolam) under resting conditions and during experimentally induced anxiety?

Study Type:
Human clinical intervention trial

Study Design:
Double-blind, placebo-controlled, repeated measures design. Volunteers took L-theanine, alprazolam, or placebo while in a resting state or under conditions of induced anxiety. Subjective self-reports of anxiety including Beck Anxiety Inventory (BAI), Visual Analog Mood Scale (VAMS), and State-Trait Anxiety Inventory (STAI) were collected before and after ingestion.

Dosage:
200 mg

Participants:
16 healthy volunteers

Results:
L-theanine showed relaxing effects when taken in the resting state. Compared to placebo, neither alprazolam nor L-theanine reduced anxiety during the anxious state.

Conclusion:
“The findings suggest that while L-theanine may have some relaxing effects under resting conditions, neither L-theanine nor alprazolam demonstrate any acute anxiolytic effects under conditions of increased anxiety in the AA model.”

The amino acid L-theanine has been shown to increase the production of alpha brain waves, which indicate a relaxed state of alertness. This effect contributes to a feeling of relaxation and may ease the transition from wakefulness to sleep. Studies suggest that L-theanine also increases brain levels of serotonin, dopamine, and levels of GABA, an inhibitory neurotransmitter with calming effects. It has affinity for AMPA, Kainate, and NMDA receptors. Finally, L-theanine may have anti-stress effects by blocking the binding of L-glutamic acid to receptors that cause the excitation of brain cells.