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Wild yam (Dioscorea villosa) is a species of tuberous vine in the family Dioscoreaceae. It is native to the eastern half of North America. The plant is low-creeping and twining, and can tolerate average to poor soil. Wild Yam's signature is its knotted and contorted root stalk, vines, and its large heart shaped leaves. Other names for the plant include China root, colic root, and rheumatism root.
Wild yam is most famous for its saponins, which can be altered chemically to produce progesterone, a steroid hormone involved in the female menstrual cycle. It is believed that wild yams contain properties similar to dehydroepiandrosterone (DHEA). These properties act as precursors to estrogen and progesterone, both of which are female sex hormones. Based on this information, many products have been manufactured containing some form of the plant.
Wild yam extract has been used to treat pain associated with menstruation and many symptoms of menopause. Its active ingredient, diosgenin, is used to synthesize a number of steroids, including estrogen and progesterone. However, this conversion can only take place in a laboratory through chemical processes. The body cannot convert diosgenin into progesterone naturally.
In traditional herbal medicine, wild yam extract is used to treat inflammatory conditions such as inflammation of the digestive tract. It is also considered to be antispasmodic, and it has a balancing effect on the entire digestive system. It is used to effectively treat spasms of the colon, stomach cramps, and to relieve pain.
Early settlers in North America once used the root to treat colic. It has also been used to treat a wide range of muscle disorders and asthma. Related species of the common North American wild yam have been used to treat colds, boils, arthritis, hemorrhoids, rheumatism, and fever in Central America and the Amazon. However, modern science has yet to study the plant in great enough detail to determine how effective it is for such disorders.
Wild yam is often prepared at home to be used for an upset stomach. A popular alternative medicine method of preparation consists of powdering the herb and placing in capsules. Two capsules are taken per day until the stomach problems have passed. A tincture of wild yam can also be taken for this purpose.
Wild yams should be avoided during pregnancy, or in the case of peptic ulcers. The herb can aggravate these ulcers in some people. People who are experiencing thyroid disorders, diabetes, hypoglycemia, urinary tract infections, leukemia, and hepatitis should also avoid consuming wild yams.
@irontoenail - To some extent I think they haven't really been studied because people use them for things that they aren't likely to be able to help with.
They do have some chemicals in them that can be changed to hormones, which is why people use them for troubles stemming from hormones, like menopause. But, it's really unlikely that the chemicals they contain are able to change into hormones in the human digestion system.
I would also be wary of using over the counter products. Wild yam creams and supplements will probably be safe use, but I don't think they would have very much effect on conditions, except as a placebo.
I think a lot of people mistake this root for Japanese yams, which are also touted for their health benefits but in an entirely different way.
They get used more as a healthy foodstuff (and they aren't really "yams" as people in the States think of them), whereas the wild yam is used more as a medication.
Wild yam uses haven't been studied though, so I would be careful in just digging it up and trying to do something with it. Try buying ready made products instead if you want to give it a go.