L-Theanine

L-Theanine is an amino acid found in green tea that has soothing neuroprotective qualities.  When taken alone it promotes feelings of calm and relaxation.  It is the only substance known to increase alpha waves in the brain, which are associated with meditation and states of relaxed contemplation. Modern studies have shown benefits in relation to stress and relaxation.

L-Theanine has an anti-stress effect:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728665/
https://www.ncbi.nlm.nih.gov/pubmed/16930802

Alpha brain waves prmoted by theanine:
https://koreamed.org/SearchBasic.php?RID=0124KJN/2003.36.9.918&DT=1