Agnus Castus acts on the pituitary gland where one of its effects is to stimulate the production of the luteinising hormone. The luteinising hormone is involved in the development of a small gland in the ovary called the corpus luteum where progesterone is made. If the corpus luteum does not develop properly the luteal phase second half of the cycle is reduced & too little progesterone is produced resulting in premenstrual syndrome irregular menstrual cycles abnormal bleeding period pains