Vitex agnus-castus is the scientific name for the plant commonly referred to as chasteberry, Vitex, or Monk’s pepper. Chasteberry is a member of the Verbenaceae family.  This medicinal plant is native to the Mediterranean and Central Asia where it has a long history of use by herbal healers, including Hippocrates and Dioscorides. Ancient uses for chasteberry included birth control and suppression of libido, especially in monks.
Botanically, chasteberry plants appear as a deciduous perennial shrub, which grow to heights between 6 and 25 feet.  The fruit of the plant is primarily used and appears as tiny black peppercorns, possessing a pepper-like aroma and flavor. The leaves are occasionally used medicinally and appear as 2 - 6 inch long leaflets that are dark green above and gray underneath. Slender spikes of lavender/blue flowers are sometimes used in medicines as well.
Chasteberry contains a number of active constituents, most of which are found in other plants. The only unique component that has been identified solely in chasteberry is an iridoid glycoside called agnuside.  Other active constituents include flavonoids (castican, orientin and isovitexin); iridoid glycosides (aucubin and eurostoside); volatile oils (0.8 - 1.6%): terpenoids (cineole, sabinene, limonene, camphene), a- and b-pinene; and 3-ketosteroids; likely progesterone, and 17-hydroxyprogesterone.
Much of the research on the pharmacology of vitex focuses on the effects of this plant upon the pituitary gland. Studies have shown that vitex can inhibit prolactin production by binding to dopamine receptors found in the pituitary gland. [4, 5] Inhibition of prolactin synthesis effects the female reproductive system by enhancing growth of the corpus luteum, thereby increasing progesterone levels.  Furthermore, vitex has also demonstrated effects on anterior pituitary production of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Vitex increases LH production, inhibits FSH production, resulting in a relative increase in progesterone and a decrease in estrogen in women.  In men, it appears that testosterone is decreased.
Knowledge of the pharmacology of vitex is useful in the treatment of many disorders related to hormonal imbalances, specifically in progesterone deficiencies and luteal phase defects. These conditions include; acne, dysmenorrhea, endometrial hyperplasia, endometriosis, infertility, insufficient lactation, menopausal syndrome, menorrhagia, metrorrhagia, oligomenorrhea, perimenopausal depression, polycystic ovary syndrome (PCOS), oligomenorrhea, premenstrual syndrome, secondary amenorrhea, threatened miscarriage, and uterine myomas.
Actions that are ascribed to chasteberry include; pituitary adjuvant, dopamine agonist, galactagogue (lactation stimulant), emmenagogue (menstruation stimulant), FSH antagonist, LH agonist, prolactin antagonist, hepatoprotective, antiseptic, and anaphrodisiac.
As mentioned, vitex is used for many conditions related to hormonal imbalance. Problems with menstrual cycles have been examined extensively for treatment with Vitex extracts. [8-10] One particular study observed benefit for female patients with various disorders that were cyclical in nature, including polymenorrhea (shortened cycle), oligomenorrhea (infrequent cycle) and menorrhagia (increased duration of bleeding).  The results showed that long term treatment with vitex, normalized all of these conditions.
A large trial of over 1500 women with corpus luteum insufficiency was conducted to examine the effect of vitex treatment.  Researchers observed that 33% of the women were free of complaints, and 51% were in satisfactory condition following vitex therapy. Studies have also been conducted for the treatment of hyperprolactinemia with vitex and have demonstrated similar clinical efficacy. [13, 14] Another cyclical problem is secondary amenorrhea, the absence of menses with a history of normal menstruation. Patients with secondary amenorrhea who took vitex extracts demonstrated normal menses after a six month treatment period. 
Women who experience premenstrual syndrome may also benefit from treatment with vitex. Two large surveys of gynecologic practices were conducted to determine the clinical efficacy of vitex for treatment of PMS. [15, 16] In these studies, women took a liquid extract of vitex at a dosage level of 40 drops once daily in the morning. Both physicians and patients rated the treatment very highly and noted a very low incidence of side effects, like mild nausea.
Infertility can be successfully addressed using vitex, dependent on the nature of the infertility. As discussed, vitex is effective for conditions resulting from luteal phase defects and high levels of prolactin. In study, forty five women with infertility related to these issues were studied and given vitex once daily for 3 months. [17, 18] The treatment was deemed successful in 39 of the patients based on levels of progesterone, incidence of pregnancy, and lengthening of the luteal phase.
Other conditions for which vitex may be beneficial include; increasing milk production in nursing mothers, endometriosis, acne in both men and women, dysmenorrhea (menstrual cramps), mastalgia (breast pain), complaints of perimenopause, and as an antimicrobial against certain strains of bacteria such as Salmonella spp. and Staphylococcus aureus. [19-23]
Generally, vitex should be taken in the morning to coincide with the diurnal rhythm of the pituitary gland. The effect of vitex does not appear quickly. It often takes up to 3 -6 months to observe benefit in the condition being treated. However, if the problem is longstanding, it may take longer.
If taking a standardized extract (such as the German products Agnolyt or Vitalex); 40 drops or 1 capsule every morning (9 grams of fruit per 100 milliliters extract) is a sufficient dose.  Infusions of Â½ to 1 teaspoon (5 - 10 grams) of the berries or seeds in 8 oz. of hot water for 15 minutes can be administered 3 times daily, or once during the morning. Tincture doses vary according to strength (i.e. 1:5 tincture) and 3 - 10 ml can be taken in the morning. 1:2 fluid extract, in amounts ranging from 1 - 4 ml is another popular daily dose for use in the morning.
Internal vitex administration should not be recommended if a patient is pregnant or undergoing in vitro fertilization.
Potential drug interactions include progesterone drugs, oral contraceptive pills, or hormone replacement therapy. 
In animal studies, very large amounts of vitex (nearly 20 times the therapeutic dose) inhibits all aspects of anterior pituitary function; resulting in decreased pituitary, adrenal, and uterine function.  Adverse effects that have been reported in large scale trials include rare occurrences of formication, abnormal menstrual cycle changes, itching, urticaria, gastrointestinal and lower abdominal complaints, and short term headaches.
1. Tilgner S. Herbal Medicine from the Heart of the Earth. Wise Acres Press, Inc. Creswell, OR, 1999: 32-33
2. Botanical Medicine Class Notes. Bastyr University, Kenmore, WA. 2002.
3. PDR for Herbal Medicines. Medical Economics Company Inc., Montvale, NJ. 2001
4. Milewicz A et al. Armeim.-Forsch. 1993;43:752
5. Sliutz G, et al. Horm Metab Res 1993; 25(5): 253-2555. Milewicz A, Gejdel E, Sworen H, et al, Vitex agnus-castus extract in the treatment of luteal phase defects due to latent hyperprolactinemia: Results of a randomized placebo-controlled double-blind study. Arzneim Forsch Drug Res 1993; 43(7):752-6.
6. Haller J, Geb und Gynakol, 1961; 156:274.
7. Jarry H. et al. Exp Clin Endocrinol 1994: 102 (6):448-454
8. Probst V and Roth OA. Dtsch Med Wschr 1954;79(35):1271-1274.
9. Roth OA. Med Klin 1956;51:1263-1265.
10. Kayser HW and Istanbulluglu S. Hippokrates 1954;25:717-719.
11. Bleier W. Zbl Gynakol 1959;81:701-709.
12. Proppind D et al. Therapeutikon 1991;5:581-585.
13. Roeder D. Z Phytoter 1994;15(3):157-163.
14. Milewicz A et al. Arzneim-Forsch 1993;43(7):752-756.
15.Dittmar EW et al. Premenstrual syndrome: Treatment with a phytopharmaceutical. Ther Gynakol 1992;5:60-68.
16. Peteres-WelteC amd Albrecht M. Menstrual abnormalities and PMS: Vitex agnus-castus. Ther Gynakol 1994;7:49-52.
17. Propping D and Katzorke T. Treatment of corpus luteum insufficiency. Z Allg Med 1987;63:932-933.
18. Propping D et al. Diagnosis and therapy of corpus luteum insufficiency in general practice. Therapiewoche 1988;38:2992-3001.
19. Noack M. Dtsch Med Wschr 1943;9:204-206.
20. Mohr W. Hippokrates 1957;28:586-591.
21. Giss G and Rothenburg W. Z Haut Geschlechskr 1968;43(15):645-647.
22. Gregl A. Med Welt 1979;30:264-268.
23. Pepeljnjak S et al. Acta Pharm 1996;46(3):201-206.
24. Mills S and Bone K. Principles and Practice of Phytotherapy. Churchill Livingstone, Edinburgh, UK 2000:328-334.
25. Haller J. Z Geburtsh Gynakol 1961; 156(3):274-302