A single dose of L-Theanine reduced the reaction time to attention tasks.  Those who took L-Theanine had an increased number of correct answers on working memory tasks, providing evidence that it can improve attention and enhance working memory and executive functions.

Read more in this blog from Dr. Carolyn Mercer ND https://www.purelabvitamins.com/blog/l-theanine-and-stress.php