Chaste tree (Vitex agnus-castus), also known as chasteberry, has a long history of traditional use for supporting women's reproductive health, particularly in balancing menstrual cycles and managing symptoms of premenstrual syndrome (PMS). Scientifically, research suggests that chaste tree may influence the hypothalamic-pituitary-gonadal axis, thereby affecting hormone levels, including prolactin and, indirectly, progesterone.

Several clinical trials and systematic reviews have found that chaste tree extract can help reduce symptoms of PMS and cyclic mastalgia (breast pain), outcomes thought to be related to its ability to lower prolactin levels. By reducing prolactin, chaste tree may help restore luteal phase function and support endogenous progesterone production, especially in women with luteal phase defects. A 2017 systematic review in the Journal of Alternative and Complementary Medicine concluded that chaste tree extracts were more effective than placebo for PMS symptoms, which are commonly associated with progesterone deficiency.

However, direct evidence that chaste tree reliably increases systemic progesterone levels in all women is limited, and its efficacy may vary between individuals. Most studies focus on symptom improvement rather than direct measurement of progesterone. Overall, while there is moderate scientific support for chaste tree's role in supporting the progesterone body system via hormonal modulation, more rigorous research specifically focused on progesterone is needed.