DescriptionL-Theanine is a naturally-occurring, unique amino acid found in green tea leaves. NuMedica s L-Theanine is Suntheanine the brand which has been used in scientific studies. L-Theanine may promote a sense of relaxation without causing drowsiness. It has also been found to promote healthy cellular function and reduce feelings of stress and anxiety. L-theanine may be useful in reducing the negative side effects of caffeine.