Chastetree (Vitex agnus-castus), also known as chasteberry, has a long history of traditional use for female reproductive health, particularly for conditions thought to be related to hormonal imbalances. Modern scientific research has investigated its effects on the hypothalamic-pituitary-gonadal axis, with particular attention to its ability to modulate prolactin secretion and potentially influence the menstrual cycle.

The primary mechanism of action is believed to involve dopaminergic compounds in chastetree that inhibit prolactin release from the pituitary gland. Lower prolactin levels can help restore the balance between estrogen and progesterone, especially in women with luteal phase defects or premenstrual syndrome (PMS). Several randomized, placebo-controlled trials and meta-analyses have shown that Vitex agnus-castus may reduce symptoms of PMS, including breast tenderness, irritability, and mood changes, and improve menstrual regularity. These benefits are thought to be due to its indirect effects on estrogen and progesterone, rather than a direct increase in estrogen itself.

While there is scientific support for the use of chastetree in PMS and some menstrual irregularities—conditions associated with the "estrogen body system"—evidence for its use in direct estrogen modulation or for estrogen deficiency (such as in menopause) is limited. Thus, its role is best described as supporting hormonal balance rather than directly supporting estrogen levels.