Chasteberry is frequently called by its Latin names: vitex or, alternatively, agnus-castus. A shrub in the verbena family, chasteberry is commonly found on riverbanks and nearby foothills in central Asia and around the Mediterranean Sea. After its violet flowers have bloomed, a dark brown, peppercorn-size fruit with a pleasant odor reminiscent of peppermint develops. This fruit is used medicinally.

As the name implies, for centuries chasteberry was thought to counter sexual desire. A drink prepared from the plant's seeds was used by the Romans to diminish libido, and in ancient Greece, young women celebrating the festival of Demeter wore chasteberry blossoms to show that they were remaining chaste in honor of the goddess. Monks in the Middle Ages used the fruit for similar purposes, yielding the common name "monk's pepper."

The modern use of chasteberry dates back to the 1950s, when the German pharmaceutical firm Madaus Company first produced a standardized extract. This herb has become a standard European treatment for cyclic breast tenderness, a condition related to PMS that is sometimes called cyclic mastitis, cyclic mastalgia, mastodynia, or fibrocystic breast disease. Chasteberry also appears to be useful for general PMS symptoms.

Chasteberry is believed to work by suppressing the release of prolactin from the pituitary gland.1-4 Prolactin is a hormone that naturally rises during pregnancy to stimulate milk production. Inappropriately increased production of prolactin may be a factor in cyclic breast tenderness, as well as other symptoms of PMS.

Elevated prolactin levels can also cause a woman's period to become irregular and even stop. For this reason, chasteberry is sometimes tried when menstruation is irregular, or stops altogether (amenorrhea). Note: We recommend that you do not attempt to self-treat significant menstrual irregularities without a full medical evaluation. There could be a serious medical condition causing the problem that you wouldn't want to miss.

High prolactin levels can also cause infertility in women. For this reason, chasteberry is sometimes tried as a fertility drug;5however, the two double-blind studies performed to evaluate this possible use failed to return statistically significant results.6,7

Chasteberry is sometimes used for menopausal symptoms, but there is as yet no evidence that it is effective, either alone or in combination with other herbs.19

A review of 13 randomized trials evaluated chasteberry for managing PMS and premenstrual dysphoric disorder (a more severe form of PMS associated with psychiatric symptoms). Chasteberry was associated with reduced PMS symptoms including breast pain, and regulation of the menstrual cycle when compared to placebo, vitamin B, or magnesium oxide. However, there was no clear benefit for premenstrual dysphoric disorder symptoms when compared to an antidepressants.24