The use of lentinan or shiitake extracts containing said active ingredient in preventing and treating endometriosis is described. Formulations are also described that are suitable for systemic administration (oral, intravenous, intramuscular) and formulations suitable for topical administration (vaginal, anal) comprising said active ingredient or the shiitake extract, optionally in combination with reishi and/or agnus castus extract, and optionally at least one active ingredient selected from at least one of the following classes consisting of antioxidants, vitamins and hormones.
