Pure Encapsulations L-TheaninePure Encapsulations L Theanine Pure Encapsulations L Theanine is a relaxation supplement that may help soothe irritability* and encourage a calmer, more focused state of mind.* But what is L theanine and how does your body use it? L theanine is an amino acid thats found in different types of teas and other foods. When ingested, this natural compound can have a relaxing effect and help you handle everyday, occasional stressors with a little more ease.*