Doctor's Best L-Theanine with Suntheanine is a unique amino acid found in green tea that supports relaxation, mental focus and a healthy stress response. This formula contains Suntheanine®, a patented form of L-theanine that has been the subject of numerous safety studies and human clinical research. Research has shown that supplemental L-theanine crosses the blood-brain barrier within 30 minutes of intake and exerts its effects directly on the brain. L-Theanine is best known for its unique ability to support relaxation without causing drowsiness.