Wild yam is a diverse herb with many uses, how it is taken determines the effect on the body, it also makes a difference in what form the herb is taken, the tea has a different effect than the powder or tincture, just as taking it as a hot tea has a very different effect than taking a tincture in cold water, as you saw in the examples for possible uses above. Wild yam can be used to both promote and decrease fertility, the different effects are achieved by the amount taken and when and how long the herb is used each cycle. When wild yam is used in moderate doses, for the first half of the menstrual cycle, from menses to ovulation then discontinued for the remainder of the cycle, the effect is to increase fertility. When wild yam is used in contraceptive doses, and is taken daily throughout the cycle, the effect is to reduce fertility and when taken correctly, can act as a contraceptive.


http://www.sisterzeus.com/wildyam.htm

you will read it hear but i heard it from a natual Dr.. and it has to be taken every day and you cannot miss a dose or you have to start over it takes a month or so to take effect like most birth controls