Initial Posting: 1/9/2015    Last Update: 8/4/2017
Answer: L-theanine is an amino acid found in green and black tea. When given as a supplement in amounts higher than in a cup of tea, preliminary studies suggest a number of effects, such as improving mental alertness, reducing stress, and enhancing the quality of sleep -- although it does not cause drowsiness.
ConsumerLab.com has tested the quality of popular brands of L-theanine. You can find out how these L-theanine supplements fared in the tests; how they compare on quality and ingredients; which offer the best value; and learn about proper dosage and potential side effects in ConsumerLab.com's Review of L-Theanine Supplements >>