Madagascar periwinkle has been widely distributed for long enough that it has gained medicinal uses for a variety of purposes far from its native land of Madagascar. Most notably, the plant is or has been used for diabetes in places as diverse as Madagascar, South Africa, Jamaica, Suriname, Vietnam, the Philippines, India, and Australia. Studies using animal models of diabetes have found that crude extracts of Madagascar periwinkle do reduce blood glucose levels. The mechanism of action of this activity is not understood, although the alkaloids now used to treat leukemia were discovered by researchers investigating the plant’s antidiabetic potential. High blood pressure is another condition sometimes treated with Madagascar periwinkle; as noted under “Toxicity,” large doses of the plant can cause hypotension, indicating the plausibility of this use. Although two of the bisindole alkaloids from Madagascar periwinkle (vincristine and vinblastine) are used as pharmaceutical drugs to treat leukemia and Hodgkin’s disease, crude extracts of the plant do not contain enough of these compounds that they could be used as effective cancer treatments (if they did, they would be extremely toxic), and there is little or no folk use for similar purposes.
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