L-theanine is an amino acid found in tea. Evidence suggests that it can partially activate the N-methyl-D-aspartate (NMDA) glutamate receptor in humans and animals and that this causes a reduction in excitation in the brain along with a concomitant increase in calmness due to generation of alpha brain waves. Because of its calming effects, L-theanine has been researched with regard to its effects in attention deficit hyperactivity disorder with and without caffeine. In the study, boys aged 8 to 15 years who had been diagnosed with ADHD were administered L-theanine (2.5 mg/kg) with and without caffeine (2.0 mg/kg) or a placebo, and then their attentive state was tested experimentally 1 hour after ingestion of the supplements. Both L-theanine and caffeine had a significant effect on cognition as would be expected from other studies. Further, L-theanine and caffeine in combination was associated with a decreased task related reactivity of a brain network associated with mind wandering suggesting that it was having a beneficial effect on the ADHD. As both L-theanine and caffeine are present in tea, this may suggest that drinking tea is beneficial to cases of ADHD.
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