What is Agnus Castus? Agnus Castus is a herb. The dried fruit, which has a pepper-like aroma & flavour, is used in herbal medicine preparations. Its Botanical name is Vitex agnus-castus. The name Agnus Castus derives from the Greek for chaste. According to Pliny, writing in the first century, Greek women wishing to preserve their chastity placed leaves of this plant on their beds & slept on them. Agnus castus can help post-menopause, to minimise night sweats, hot flushes & fatigue.