Science-Based Nutrition Helps Boost Nitric Oxide (NO) Levels to Support Overall Cardiovascular Health Dietary Supplement Non-GMO - Gluten Free - Soy Free - Vegan Doctor's Best Sustained plus Immediate Release L-Arginine contains this essential amino acid in a bilayer tablet, with two tablets providing 500 mg of sustained release and 500 mg of immediate release L-arginine in a formula that delivers enhanced blood levels. These tablets are specifically manufactured to immediately increase blood levels of L-arginine and then to sustain this beneficial increase continuously over an 8-hour period. Research suggests that arginine supplementation helps increase muscle mass and may also positively beneficial in improving endurance as it a precursor to creatine, which helps supply energy to all cells of the body. L-arginine has been shown to support the cardiovascular system, heart function and improve overall circulation through its conversion to nitric oxide. Helps support athletic endurance Helps support recovery from athletic performance