More than half of all U.S. states have legalized cannabis, be it for medical purposes, recreational use, or both. The shelves of cannabis dispensaries offer an ever-widening array of gummies, drinks and joints. Meanwhile, the federal government still considers most types of cannabis illegal. A new report from the National Academies of Sciences, Engineering and Medicine, released this week, finds this disconnect between the states and the federal government is leading to fragmented policies, and…