Stress Management 100 mg Suntheanine Supports Cardiovascular Function Promotes Relaxation GMP Quality Assured A Dietary Supplement Vegetarian Formula L-Theanine is an amino acid naturally found in green tea. L-Theanine promotes relaxation without the drowsiness or negative side effects associated with other calming agents. L-Theanine also supports healthy cardiovascular function through this relaxing effect as well as its antioxidant properties.