Cannabis oil for cancer or Rick Simpson Oil (RSO), oil made from the flowers of the cannabis (marijuana) plant, gets attention online from people who claim it treats cancer. Some early on research suggests that some chemicals in marijuana have future potential as a cancer treatment. Cannabis oil comes in many types and formulations. These include cannabidiol (CBD) oil, which is often part of medical marijuana. Unlike many other cannabis oils, pure THC oil for cancer is high in tetrahydrocannabinol (THC), which is the main psychoactive chemical in marijuana. THC is the chemical in marijuana that provides the "high."