Dioscorea villosa, commonly known as wild yam, is native to Canada and the southern United States. It is one of an estimated 600 species of yam in the genus, Dioscorea, found in warm tropical habitats. Many of these are wild species that flourish in damp woodlands and thickets.

Yams are important cultigens, and some yam species are major food staples in tropical countries. The potato-like tubers of yam plants are grown as both edible and ceremonial plants throughout the world, even in subtropical and temperate regions. The formation and morphology of the tubers can vary from species to species. The tubers of Dioscorea villosa, for example, arise as fleshy rhizomes.

The tubers of wild yam and certain related species contain saponin compounds, including steroid-like constituents that are used as starting material for the synthesis of hormones. Wild yam tubers contain diosgenin, a steroid precursor that can be converted into the female hormone progesterone in the laboratory. 

The discovery of diosgenin revolutionized the pharmaceutical industry several decades ago. It paved the way for synthesizing hormones and developing oral contraceptives. Today, diosgenin is still used as an active industrial agent in the half-synthesis of steroidal hormones. This chemical compound was traditionally obtained from Mexican yam (Dioscorea mexicana), but it is also present in wild yam (Dioscorea villosa). Wild species of yam tend to contain higher concentrations of diosgenin than do cultivated, edible species.

A closely related species of wild yam, Dioscorea alata, is used in the Amazon as a treatment for fever, gonorrhea, leprosy, piles, and tumors. Amazonian medicinal plant remedies made from other Dioscorea species are administered for skin inflammation, stomachache, boils, cancer, dysentery, goiter, and syphilis. In Belize, a "wild yam" species (Dioscorea belizensis) is a popular treatment for urinary tract infections, cold, bilious colic, rheumatism, arthritis, and diabetes.

Both cultivated and uncultivated yam species are employed in folk medicine for a wide variety of ailments. Diosgenin is conceivably responsible for pharmacological activities such as the purported anti-inflammatory effects of wild yam. The tubers of Dioscorea villosa and other wild yam species have a long history of use in traditional herbalism, but their importance will forever be linked to modern medicine. The synthesis of hormones and the birth control pill from diosgenin marks one of the major advances in plant drug medicine this century. This discovery helped to legitimize ethnopharmacology—the search for pharmaceutical drugs from natural products, particularly natural products from the plant kingdom.

Wild yam is a perennial, twining vine with pale brown, knotty, woody, cylindrical rootstocks, or tubers. The rootstocks are crooked and bear lateral branches of long creeping runners. The thin reddish-brown stems grow to a length of 5 to 12 meters. The tubers have no characteristic odor. The roots initially taste starchy, but soon thereafter become bitter and acrid to the tongue.

The wild yam plant has clusters of small green-white to green-yellow single flowers that are sessile-like. The heart-shaped leaves are broadly ovate and long-stemmed, with prominent longitudinal veins. The leaves are glabrous on the upper surface and pubescent on the underside.

Part Used/Pharmaceutical Designation

• Dried rhizome with roots

Dioscorea villosa roots contain saponins (e.g., dioscin, an aglycone diosgenin), isoquinuclidine alkaloids (e.g., dioscorin)

Commercial preparations of wild yam are available as liquid extracts and powdered tuber products. Raw plant material for commercial use is typically harvested from the eastern and central United States, and supplied to commercial outlets in the form of cut or broken tubers.

Traditional uses: used as anti-inflammatory, cholagogue (stimulates flow of bile to duodenum), antispasmodic, carminative, sudorific, mild diaphoretic (perspiration-promoting agent), anodyne (analgesic), emetic (vomit-causing agent), expectorant; used for rheumatic conditions, gallbladder colic, dysmenorrhea, cramps, asthma, diuretic, dyspepsia, liver ailments, parturition, uterotonic, pain and inflammation of diverticulai, bilous colic, nausea associated with pregnancy, cramps, neuralgia, spasmodic hiccup, spasmodic asthma, women's reproductive health (e.g., salve made from inner root applied topically for breast inflammation and postmenopausal vaginal dryness).

Conditions: inflammation, spasm, rheumatic conditions, cramps; mild diaphoretic.

Clinical applications: anti-inflammatory, cholagogue, antispasmodic, mild diaphoretic, rheumatic conditions, gallbladder colic, dysmenorrhea, cramps, biliousness, nausea, intestinal colic.

Although various species of Dioscorea have been investigated extensively for their pharmacological properties, relatively few published studies were located on Dioscorea villosa. Various preparations of wild yam reportedly have exhibited anti-inflammatory, antitumor, estrogenic, hemolytic, hypocholesterolemic, amebicidal, mastogenic (pertaining to breasts), pesticidal, and piscicidal effects. However these claims have not necessarily been confirmed by laboratory research. Similarly, the putative antifatigue, antistress, and antigliomic (antitumor against cancers of brain and nervous tissue) effects of wild yam await further scientific verification.

However, studies on other species of Dioscorea clearly show that a related species of wild yam has antidiabetic activity. In one investigation, the effects of hydroalcoholic extracts of Dioscorea dumetorum tubers were evaluated on either fasting normal mice or rabbits, and on fasting alloxan-diabetic rabbits. Both the whole extract and the steroidal fractions, especially the glycosidic portion, produced significant hypoglycemic action in normal test animals and in fasting alloxan-diabetic rabbits. A fraction containing alkaloids actually elevated blood sugar in the fasting normal mice. This suggests that the active constituent responsible for the hypoglycemic effect is probably a steroidal derivative. Nigerian researchers have also reported that Dioscorea dumetorum tubers possess antidiabetic properties.

• Dried herb: 1 to 2 tsp tid
• Tincture: 2 to 4 ml tid

No adverse side effects have been reported for wild yam preparations when taken in recommended therapeutic dosages.

Warnings/ Contraindications/Precautions

Overdosing can be potentially poisonous because dioscorin, one of the active constituents, can have picrotoxin-like effects.

Dietary provisions of diosgenin (1% w/w) for 6 days reduced the cholestatic effects of estradiol-17b-(b-D-glucuronide) (1.1 mmol/100g IV) in rats (Accatino et al. 1998). In addition, the diosgenin-supplemented diet prevented some of the cholestatic effects of 17 a-ethynylestradiol (5 mg/kg subcutaneously), such as increased biliary alkaline phosphatase and decreased taurocholate SRm.

Wild Yam is listed in the British Herbal Pharmacopeia.

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