Why Olive Leaf? Medicinal use of olive leaves dates back to ancient Egypt. Now used throughout the world, a growing body of scientific research points to the health benefits of Oleuropein, a powerful antioxidant found within this potent leaf. The leaves we use in Barlean’s Olive Leaf Complex are sourced from the Andalusian regions of Spain. These healthy leaves are teeming with Oleuropein, as well as a wide range of polyphenols.