Alkaloids tend to taste bitter, so alkaloid-filled leaves are avoided by grazing herbivores. Many also interfere with processes in animal cells, which makes them poisonous. The Madagascar Periwinkle produces over 120 such alkaloids, including vincristine and vinblastine.
The Madagascar Periwinkle has been used for centuries as a folk remedy for diabetes, and this led to studies investigating its use as a medicine. These studies showed little effectiveness in treating diabetes, but great potential in stopping the division of rapidly dividing cells, leading to its use in anti-cancer therapies, particularly for treating childhood leukaemia. The active ingredient vincristine is produced at a yield of only three grams per tonne of plant material and, for a while, farms were devoted to the growth of the plant. However, vincristine can now be synthesised in a laboratory.