Vincristine is a chemotherapy drug, primarily used to treat certain types of leukemia. It can also be used as an immunosuppresant to treat thrombotic thrombocytopenic purpura and other similar conditions. It is derived from a species of the periwinkle plant.
Vincristine works by blocking a key protein involved in the separation of chromosomes during cell division. Instead of multiplying, the cell instead undergoes apoptosis, essentially self-destructing itself.