Vitex agnus-castus, also known as chaste tree berry, is supported by scientific evidence for use in premenstrual syndrome (PMS), including PMS Type S (symptoms dominated by swelling and fluid retention, attributed to estrogen excess and/or progesterone deficiency). Multiple randomized controlled trials and systematic reviews have investigated Vitex for PMS. A 2017 Cochrane review (Cochrane Database Syst Rev. 2017) concluded that Vitex may be more effective than placebo in reducing overall PMS symptoms, including mastalgia, bloating, and edema, though the quality of evidence was moderate and more research was recommended.

The proposed mechanism involves modulation of pituitary function, particularly a dopaminergic effect that reduces prolactin levels. Lower prolactin may indirectly increase luteal phase progesterone, addressing the relative "estrogen excess/progesterone deficiency" thought to underlie PMS Type S symptoms. Historical and traditional use of Vitex for menstrual irregularities and PMS also exists, but modern trials provide moderate support for its efficacy, especially for somatic symptoms such as breast tenderness and bloating.

Overall, while evidence is not definitive and more large-scale studies are needed, current data support the use of Vitex agnus-castus as a reasonable option for PMS, including PMS Type S, with a moderate level of scientific validation.