The Nature LibraryEN·ES
← The ApothecaryDioscoreaceaetuberFact-checked 24 October 2026

Bitter yam

Dioscorea dumetorum

Also calledTrifoliate yam · Ngamba (Kongo, DR Congo)

In older monographsHelmia dumetorum, Dioscorea triphylla var. dumetorum, Dioscorea buchholziana

A West and Central African yam, the most nutritious of the region's eight common yam species, whose deep-yellow tubers are also used in Nigeria and DR Congo to treat diabetes. Its compound dioscoretine lowers blood sugar in animals, but raw or undercooked tubers contain the convulsant alkaloid dioscorine and cause poisoning with seizures.

What it is used for

  • Used in traditional antidiabetic treatment in Nigeria and by healers in Kinshasa. Dioscoretine (20 mg/kg by injection) and the aqueous fraction of the tuber extract lowered blood sugar in normal and alloxan-diabetic rabbits, comparably to tolbutamide; the glycoside fraction was also active in mice. The alkaloid fraction raised blood sugar. No human trials.1,2,3,4

  • Methanolic extracts of non-edible D. dumetorum showed antibacterial activity in the lab, strongest against Proteus mirabilis.5

How it is prepared

food

Tubers must be fully cooked (about an hour in the Ile-Ife community) or soaked in water and dried before eating; post-harvest hardening within 24 hours makes stored tubers inedible.

Amounts are as recorded by the named source, not a recommendation.

Safety

Pregnancy
Insufficient data
Breastfeeding
Insufficient data

Interactions with medicines

  • diabetes medicines (insulin, sulfonylureas)ModerateDioscoretine lowered blood sugar about as much as tolbutamide in rabbits; additive hypoglycaemia is possible.
Interaction checker →

Do not use if

  • Eating raw or undercooked tubers

Side effects

  • Itching and allergic reactions attributed to histamines in the tuber

In the healing traditions

  • African traditional medicine

    Bitter yam (Nigeria); Ngamba (Kinshasa)

    Deep-yellow tubers used in Nigerian antidiabetic treatment; tuber preparations among the antidiabetic remedies of herbalists and traditional practitioners in Kinshasa, DR Congo. The tuber is also a staple food once properly processed.

Active compounds

dioscoretine
hypoglycaemic compound of the tuber; LD50 0.58 g/kg in mice
dioscorine
convulsant alkaloid responsible for nervous-system and digestive poisoning from raw or undercooked tubers
steroidal glycosides
fraction with prompt hypoglycaemic action in rabbits

History

A convulsant alkaloid from this yam was reported in Nature in 1956. In the 1980s and 1990s Nigerian pharmacologists tested the tuber's traditional antidiabetic use and isolated dioscoretine; the species' genome was sequenced in 2020 to help breed varieties that do not harden after harvest.

Sources

  1. 1.Iwu MM et al. Hypoglycaemic activity of dioscoretine from tubers of Dioscorea dumetorum in normal and alloxan diabetic rabbits. Planta Med 1990 (abstract)
  2. 2.Undie AS, Akubue PI. Pharmacological evaluation of Dioscorea dumetorum tuber used in traditional antidiabetic therapy. J Ethnopharmacol 1986 (abstract)
  3. 3.Siadjeu C et al. High contiguity de novo genome sequence assembly of trifoliate yam (Dioscorea dumetorum) using long read sequencing. Genes 2020
  4. 4.Chiribagula Valentin B et al. Ethnomedicinal knowledge of plants used in nonconventional medicine in the management of diabetes mellitus in Kinshasa (DR Congo). Evid Based Complement Alternat Med 2023
  5. 5.Chandrasekara A, Josheph Kumar T. Roots and tuber crops as functional foods: a review on phytochemical constituents and their potential health benefits. Int J Food Sci 2016
  6. 6.Eke UC et al. Toxic encephalopathy following undercooked bitter yam ingestion in two patients in Ile-Ife, Nigeria: a case report. Case Rep Neurol Med 2025
  7. 7.Siadjeu C et al. Genetic diversity and population structure of trifoliate yam (Dioscorea dumetorum) in Cameroon. BMC Plant Biol 2018
  8. 8.Bevan CW, Broadbent JL, Hirst J. A convulsant alkaloid of Dioscorea dumetorum. Nature 1956 (title only)

Reference, not prescription. Nothing here is medical advice. Herbs can interact with medicines and be dangerous in pregnancy; tell your doctor or pharmacist about anything you take.