Pterostilbene is a very similar molecule to Resveratrol's, but where Resveratrol has three hydroxyl groups at its extremities, two of them are replaced with methoxy groups in Pterostilbene. This difference makes Pterostilbene far more bioavailable than Resveratrol, it's more easily absorbed through the stomach lining and cell membranes and stays in one's system longer, giving it similar, but more powerful effects.