Chinese Chastetree (Vitex negundo) has been traditionally used in various Asian medical systems, including Traditional Chinese Medicine (TCM) and Ayurveda, for conditions involving pain, inflammation, and hormonal imbalances. However, most modern research and clinical studies focus on the European species, Vitex agnus-castus (commonly called chasteberry), which has shown some benefits in relieving symptoms of premenstrual syndrome (PMS), such as breast swelling and tenderness (mastalgia). The mechanism is thought to be related to modulation of prolactin levels via dopaminergic activity.

For Vitex negundo specifically, there is limited but promising scientific evidence. Some preclinical studies indicate anti-inflammatory and analgesic properties, and traditional texts mention its use for breast pain and swelling. However, high-quality human clinical trials directly evaluating its efficacy for breast tenderness or mastalgia are lacking. Thus, while there is a plausible pharmacological basis and some preliminary support, the evidence is not as robust as for Vitex agnus-castus.

In summary, Chinese Chastetree is used traditionally for breast swelling and tenderness, and there is some scientific rationale from animal and in vitro studies. The overall level of clinical evidence is moderate (rated 3/5), primarily based on historical use and pharmacological properties, but more rigorous clinical trials are needed to fully validate its effectiveness for this indication.