Agnuside is an iridoid glycoside found primarily in the fruit of Vitex agnus-castus (chasteberry), a medicinal plant used for centuries in traditional medicine to address various female reproductive health concerns, particularly those believed to be related to hormonal imbalances. In traditional European and Mediterranean herbal practices, chasteberry has been used to alleviate symptoms of premenstrual syndrome (PMS), regulate menstrual cycles, and support fertility—effects that are often attributed to an increase in progesterone or a rebalancing of the estrogen/progesterone ratio.

While modern research has identified agnuside as one of the primary active compounds in Vitex agnus-castus, there is limited direct scientific evidence specifically linking agnuside alone to increased progesterone production. Most clinical studies and mechanistic investigations focus on whole chasteberry extracts rather than isolated agnuside. Some studies suggest that chasteberry may exert its effects by influencing the pituitary gland, leading to altered secretion of prolactin and potentially promoting a hormonal environment favorable to increased progesterone activity, though results are mixed and mechanisms remain unclear.

Therefore, while there is a strong traditional basis for using agnuside-containing plants to support the progesterone body system, direct scientific validation for agnuside itself is limited. The overall evidence for the use of agnuside (via chasteberry) in progesterone-related support is moderate, primarily rooted in longstanding traditional use rather than robust clinical trials on agnuside alone.