Madagascar periwinkle is an ornamental flowering plant with dark green, glossy leaves and rose, pink and white rounded-edge, star-shaped flowers. During World War II, it was discovered that when ingested, its leaves worked as a substitute for insulin in diabetic soldiers.
Further research throughout the 1950s revealed that Madagascar periwinkle had little effect on blood sugar levels, but it did appreciably reduce white blood cells without side effects, according to Dr. T. Ombrello at the UCC Biology Department. Two highly toxic substances present in the plant leaves - vinblastine and vincristine - are used in the treatment of cancer. WebMD reports that the Madagascar periwinkle is also used to treat sore throats, coughs and fluid retention.