Encountering difficulties conceiving and carrying a child is a heartbreaking experience, one that 10 percent of American couples face after a year of trying. While conventional fertility treatments can help, they're often difficult and expensive procedures. Women looking for an herbal alternative may have one in the berry of the chaste tree (Vitex agnus-castus), which has been used medicinally for centuries and even noted by Hippocrates for its effects on female reproduction. Also known as "monk's pepper," because of its purported ability to weaken male libido, this herb is being used today to help women having trouble conceiving due to a weak second half of their cycle or low progesterone.
The fruit of the small, shrubby native of Eurasia bearing spikes of rose-lavender flowers, chaste tree berry, like many herbs, has not been studied extensively. In fact, there have been no studies to determine its efficacy with fertility. The pooled results from three large German studies found that chaste tree berry completely relieved premenstrual syndrome (PMS) symptoms for about one-third of the 4,500 participants, with half reporting marked improvement. But further testing yielded more than just relief from PMS. In one study with 45 participants, seven women who previously had difficulty conceiving became pregnant.
Although chaste tree berry hasn't been subjected to study in the United States, German research suggests a dose of 30-40 mg/day may help patients normalize their progesterone level after three months of therapy (progesterone is needed to sustain a pregnancy). Since the supplement seemed to stabilize the second half of the women's cycle, when ovulation occurs, researchers hypothesize that this may help some women get pregnant.
While side effects of chaste tree are rare and typically mild, including gastrointestinal upset, headaches, and increased menstrual flow, there has been one case reported of ovarian hyperstimulation, a potentially life-threatening condition where the ovaries produce multiple eggs. The condition was corrected once use was discontinued. Furthermore, as chaste tree berry interacts with the hormone prolactin, it can make birth control pills less effective. Women considering treatment involving chaste tree berry should do so under the care of an ob-gyn and licensed herbalist.