Ellagic acid is a naturally occurring substance. Plants produce ellagic acid from hydrolysis of tannins such as ellagitannin and geraniin. Medicinally, ellagic acid is used to prevent cancer and treat viral and bacterial infections.

Ellagic acid is found in oaks species like the North American white oak (Quercus alba) and European red oak (Quercus robur). Ellagic acid can be found in the medicinal mushroom Phellinus linteus. The highest levels of ellagic acid are found in blackberries, cranberries, pecans, pomegranates, raspberries, strawberries, walnuts, wolfberries, and grapes. It is also found in peach and other plant foods.