The Minnesota Department of Health last week released a study that found 4 in 10 people with difficult-to-control pain of moderate and high levels reported medical cannabis provided significant relief. Dr. Tom Arneson of the state's Office of Medical Cannabis said the research is a good starting point, but more research is needed. Arneson joined MPR News Host Mike Mulcahy for a look at what research is being done (in Minnesota and elsewhere) around medical cannabis, what scientists are learning, and which areas need more study.