L-theanine is an amino acid found most commonly in tea leaves and in small amounts in Bay Bolete mushrooms. It can be found in both green and black tea.Research indicates that L-theanine promotes relaxation without drowsiness. Many people take L-theanine to help ease stress and unwind.Paired with caffeine, L-theanine may help increase focus and attention.
A 2013 study found that moderate levels of L-theanine and caffeine (about 97 mg and 40 mg) helped a group of young adults to focus better during demanding tasks.The study’s participants also felt more alert and less tired in general. According to another study, these effects can be felt in as little as 30 minutes.