Vitex, commonly known as chaste tree or Vitex agnus-castus, is widely used to support or treat premenstrual syndrome (PMS). Its use for PMS is supported by both traditional herbal medicine practices and scientific research. The primary mechanism proposed involves modulation of the pituitary hormone prolactin, which in turn may help balance estrogen and progesterone levels. Several randomized, placebo-controlled clinical trials have investigated Vitex’s efficacy for PMS symptoms such as breast pain, irritability, mood swings, and bloating. A systematic review and meta-analysis published in 2017 found that Vitex extracts were more effective than placebo in reducing overall PMS symptoms, although the quality of evidence was moderate due to variations in study design and outcome measures. The German Commission E also recognizes Vitex for the treatment of PMS and cyclic breast discomfort. Side effects are generally mild and may include gastrointestinal upset or headaches. While the precise active constituents and mechanisms remain under investigation, the available clinical evidence suggests a beneficial effect, and major health authorities in herbal medicine acknowledge its use. However, further high-quality, large-scale studies are needed to confirm efficacy and establish optimal dosing.