In short, the jury's still out. There is evidence that it has an effect on your "system" but no studies to date have conclusive evidence that vitex actually improves fertility rates. (Note chasteberry is also known as Vitex, Vitex agnus-castus (VAC), Chaste Tree, or Monk's Pepper vitex.)
Two studies (one is the FertilityBlend Study, the other is a small German study) found improved pregnancy rates when women took it along with several other supplements - unfortunately there's no way to know which of the supplements played the beneficial role. One anecdotal study even found it interfered with a woman's fertility in a negative way.
Evidence does exist that it helps cyclical breast discomfort and premenstrual syndrome so it may affect hormone levels, but its effect on your fertility is still undetermined. Below is a list of available clinical literature.
Roemheld-Hamm B.Department of Family Medicine, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey 08901, USA. 2005.
For centuries, chasteberry has been used to treat many hormone-related gynecologic conditions. The current literature supports the use of chasteberry for cyclical breast discomfort and premenstrual syndrome; data on its use for menstrual irregularities and fertility disorders are weak. Its traditional use as a galactagogue (i.e., a substance that enhances breast milk production) is not well supported in the literature and should be discouraged. There are no clinical data to support the use of chasteberry for reducing sexual desire, which has been a traditional application. Chasteberry is well tolerated; reported adverse effects are minor and may include gastrointestinal complaints, dizziness, and dry mouth. No herb-drug interactions have been reported, but caution is advised for its concomitant use with dopamine agonists or antagonists. Optimal standardization and dosing recommendations await clarification in clinical studies.
Westphal LM, Polan ML, Trant AS. Department of Gynecology/Obstetrics, Stanford University School of Medicine, Stanford, CA 94305, USA. 2006.
PURPOSE: To determine the impact of nutritional supplementation on female fertility. METHODS: A double blind, placebo-controlled study of the effects of FertilityBlend for Women, a proprietary nutritional supplement containing chasteberry, green tea, L-arginine, vitamins (including folate) and minerals, on progesterone level, basal body temperature, menstrual cycle length, pregnancy rate and side-effects. RESULTS: Ninety-three (93) women, aged 24-42 years, who had tried unsuccessfully to conceive for six to 36 months, completed the study. After three months, the FertilityBlend (FB) group (N = 53) demonstrated a trend toward increased mean mid-luteal progesterone (P(ml)), but among women with basal pretreatment P(ml) < 9 ng/ml, the increase in progesterone was highly significant. The average number of days with luteal-phase basal temperatures over 98 degrees F increased significantly in the FB group. Both short and long cycles (< 27 days or > 32 days pretreatment) were normalized in the FB group. The placebo group (N = 40) did not show any significant changes in these parameters. After three months, 14 of the 53 women in the FB group were pregnant (26%) compared to four of the 40 women in the placebo group (10%; p = 0.01). Three additional women conceived after six months on FB (32%). No significant side-effects were noted. CONCLUSION: Nutritional supplements could provide an alternative or adjunct to conventional fertility therapies.
Bergmann J, Luft B, Boehmann S, Runnebaum B, Gerhard I. Abteilung fur Gynakologische Endokrinologie und Fertilitatsstorungen, Universitäts-Frauenklinik, Heidelberg. 2000.
OBJECTIVE AND DESIGN: In a prospective, randomized, placebo-controlled, double-blind study, the effects of Phyto Hypophyson L (Steierl-Pharma GmbH, Herrsching, Germany), an Agnus castus-containing homeopathic preparation, were investigated in 67 women with fertility disorders. PATIENTS AND METHODS: 37 women with oligomenorrhea and 30 women with amenorrhea received 50 drops of Phyto Hypophyson L or placebo 3 times a day over 3 months or 3 cycles. OUTCOME MEASURE AND RESULTS: The outcome measure being spontaneous menstruation, improved concentration of progesterone in the luteal phase, shortening of the cycle, earlier ovulation, and pregnancy was achieved in 38 out of 67 women. It was achieved more often from women with oligomenorrhea in the Phyto Hypophyson L group compared to the placebo group (82 versus 45%, p = 0.021). However, there was no significant effect when viewing the whole group. The baby take-home rate during the therapy and 6 months after the end of the therapy showed a ratio of 6 : 2 (18.7 : 6.4%). This result was not significant. Furthermore, in the oligomenorrhea verum group we observed a significant increase of progesterone during the luteal phase compared to the oligomenorrhea placebo group. Only very few undesirable drug effects were observed. CONCLUSION: In women with sterility and oligomenorrhea, a treatment with Phyto Hypophyson L can be recommended over a period of 3-6 months. Copyright 2000 S. Karger GmbH, Freiburg
Cahill DJ, Fox R, Wardle PG, Harlow CR. University of Bristol Department of Obstetrics and Gynaecology, St Michael's Hospital, UK. 1994
After three endocrinologically normal cycles while undergoing unstimulated in-vitro fertilization treatment, a woman took a herbal medicine (Vitex agnus castus) at the beginning of a fourth unstimulated IVF treatment cycle. In this fourth cycle, her serum gonadotrophin and ovarian hormone measurements were disordered. One embryo resulted from the three eggs collected but a pregnancy did not ensue. She had symptoms suggestive of mild ovarian hyperstimulation syndrome in the luteal phase. Two subsequent cycles were endocrinologically normal. We do not advocate the use of this herbal medicine to promote normal ovarian function.