L-Theanine, a non-dietary amino acid abundant in green tea, was first isolated in 1949 in Japan. It crosses the blood-brain barrier and affects alpha brain waves, leading to a state of relaxed alertness. By increasing neurotransmitters such as serotonin, dopamine, and GABA, and raising BDNF and NGF levels, L-Theanine is recognized for its ability to reduce stress, improve mood, and enhance cognition.

How does L-Theanine work?

L-Theanine exerts its effects on the brain through two main mechanisms:

Promotion of relaxation and concentration: L-Theanine enhances alpha brain waves, which are associated with mental relaxation and focus. Studies have shown that L-Theanine supplementation leads to an increase in alpha wave power, indicating enhanced relaxation and concentration.

Modulation of neurotransmitters: L-Theanine boosts neurotransmitter levels like dopamine, serotonin, and GABA, while decreasing the excitatory neurotransmitter glutamate. This balance of neurotransmitters contributes to reduced stress, tension, and agitation, promoting a state of calmness. Studies indicate that L-Theanine can lower heart rate and stress-related markers, demonstrating its anti-stress effects by preventing the stimulation of brain neurons.

What are the potential uses and benefits?

  • Enhancing the quality of sleep.
  • Alleviating anxiety.
  • Potentially preventing cancer.
  • Reducing the risk of stroke in situations of cerebral ischemia.

There are additional purported uses of L-theanine, but their efficacy has not been scientifically validated by medical professionals.

Side Effects

Although there are no reported side effects associated specifically with L-theanine intake, excessive consumption of green tea, which contains caffeine, may result in:

  • Nausea
  • Upset stomach
  • Irritability

Women who are pregnant or breastfeeding should also limit how much tea they drink to avoid over-caffeinating.

Recommended Dosage

Cardiovascular: L-Theanine doses of 50 mg or 200 mg have been found to have a beneficial effect on acute caffeine-induced cerebral hemodynamics and behaviors, as well as on stress-induced increases in heart rate and blood pressure, in healthy adults.

Schizophrenia: Adjunctive L-theanine at 250 mg/day or 400 mg/day for 8 weeks alongside current antipsychotic medication has been researched to enhance Positive and Negative Syndrome Scale (PANSS) positive and general psychopathology scores in schizophrenia patients.

Sleep disorders: Supplementing with L-theanine at doses of 250 mg/day or 450 mg/day (225 mg twice daily) for 8 weeks alongside existing antipsychotic medication has been studied for its potential to enhance specific sleep aspects in patients with major depressive disorder, schizophrenia, or generalized anxiety disorder(GAD).


[1] Nobre, Anna C et al. “L-theanine, a natural constituent in tea, and its effect on mental state.” Asia Pacific journal of clinical nutrition vol. 17 Suppl 1 (2008): 167-8.

[2] Ghosh Hajra, Sujoy et al. “Developing Brain Vital Signs: Initial Framework for Monitoring Brain Function Changes Over Time.” Frontiers in neuroscience vol. 10 211. 12 May. 2016

[3] Kimura, Kenta et al. “L-Theanine reduces psychological and physiological stress responses.” Biological psychology vol. 74,1 (2007): 39-45.

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