Agnusides are one of the primary active constituents found in the berries of Vitex agnus-castus, commonly known as chaste tree or chasteberry. The use of Vitex agnus-castus to support female reproductive health has a long history in traditional herbal medicine, particularly in Europe and the Mediterranean region. Historically, the herb has been used to address conditions believed to be related to hormonal imbalances, such as premenstrual syndrome (PMS), menstrual irregularities, and symptoms associated with menopause.

The traditional rationale for using agnusides and Vitex is based on observations of its effects on menstrual health and fertility, which were often interpreted as a balancing influence on the "female hormones," including estrogen. However, the scientific evidence for a direct effect of agnusides on estrogen levels or estrogen receptors is limited. Most of the research on chasteberry has focused on its dopaminergic effects, which can lead to decreased prolactin secretion, rather than a direct modulation of estrogen. Some studies suggest that Vitex may have mild effects on the menstrual cycle by this mechanism, but the link to estrogen support specifically is not robustly established.

In summary, the use of agnusides to support the estrogen body system is primarily rooted in tradition, with moderate evidence (historical and some preliminary clinical studies) for broader hormone-modulating effects, but with limited scientific validation for a direct estrogenic action.