While leaves from the olive tree have been used throughout history to treat a wide range of Symptom (Subject feeling)s, it was only recently that Olive Leaf supplementation gained the notoriety it rightly deserves. Known for its ability to remarkably increase the body’s response to stress, Olive leaf extract gets its immune supporting powers from oleuropein, the active ingredient. Research has shown that Olive leaf works at the cellular level to measurably strengthen the body’s immune response.