Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial

Researchers randomly assigned 30 healthy adults to take either 200 milligrams of L-theanine or a look-alike inactive pill each day for four weeks. They checked mood, anxiety, sleep quality, and thinking skills using questionnaires and simple tests. The L-theanine group reported less anxiety and depression and better sleep than the inactive-pill group. They also showed some improvement on tests of attention and mental flexibility. The study was small and lasted only four weeks.

What this means for you: L-theanine may help some healthy adults with stress or sleep, but this small study is not strong enough to justify buying it for everyone. Longer studies with more people are needed.