L-Theanine Supplement Review

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  Evaluated for:
Effectiveness Rating Effectiveness Rating
Improving mood and concentration
+2 (Moderate Evidence)
Decreasing anxiety and stress
+2 (Moderate Evidence)


  • L-theanine, a water-soluble amino acid, is found mainly in green and black tea, and to a lesser extent in mushrooms. It constitutes between 1 and 2 percent of the dry weight of tea. Passing through the blood-brain barrier within 30 minutes, it is used for stress relief, the treatment of anxiety, improved concentration and focus, and minimal cognitive impairment. It is said to generate creativity, a state of wakeful relaxation, and higher learning via the ability to ignore distracting information during complex tasks.
  • L-theanine has demonstrated benefit for patients diagnosed with anxiety by increasing levels of dopamine and GABA in the brain. It also improved test performance without the agitation caused by caffeine.
  • L-theanine is generally regarded as safe for adults in moderate amounts.


  • While some studies have found that the antagonism of caffeine’s effects by L-theanine blunts quick response time and focus, others have found that it increases focus and shortens response time. It may be due to the effect of L-theanine on attention and reaction time, helping those with high anxiety levels caused by caffeine. This may make tea less exciting than coffee, as L-theanine seems to oppose some of the focus-giving effects of caffeine.
  • L-theanine should be used with caution in patients on anti-hypertensive medicines, because it decreases blood pressure.
  • L-theanine is found naturally in both green and black tea, so I prefer drinking the tea instead of taking the supplement.

L-theanine should be used only under a doctor’s supervision if you are taking drugs for chemotherapy because it increases the activity of some cancer chemotherapeutic agents. Do not take L-theanine with cholesterol lowering medications.

DOSAGE:200 to 400 mg once or twice daily. (1200 maximum a day).

CONCLUSION:We conclude that L-theanine is a safe and effective way to help treat anxiety and improve concentration. We prefer drinking the tea leaves naturally to taking the supplement. Remember to include it in your list of supplements when you visit your doctor and other health care providers.

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Miyagawa, K. et al. Co-atministration of L-cystine and L-theanine enhances efficacy of influenza vaccination in elderly persons: Nutritional status-dependent immunogenicity. Geriatr Gerontol Int (2008) 8:243-250
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