What is L-Theanine? BULK POWDERS™ 100% pure L-Theanine Powder is a natural constituent of tea. This non-essential amino acid is made by the body with help from essential amino acids. L-Theanine is best consumed though supplementation for optimal benefits, as only small amounts are found in dietary sources. L-Theanine has been shown to effectively cross the blood brain barrier to maximise benefits in relation to brain alpha waves, which are associated with relaxation. L-Theanine is