There's not much research. There is a lot of research on the harmful effects of using cannabis. There has not been much research done on whether cannabis is useful for any medical condition. Part of this was because it was difficult to do clinical research when you were dealing with an illegal substance. To design clinical research, and to do long-term research like this.... Again, this was not a product that was developed to treat medical conditions. This is a product that people use for all sorts of reasons.
The research is scant.