Would you please provide the exact law? MAPS[1] is a non-profit specifically dedicated to gathering and allocating funding for such studies, and considering how long they've been around doing what they're doing, I'd say they've figured out how to bypass the stringent requirements and remain on this side of the law.

Full disclosure, I was involved with them briefly. The paperwork process needed to get the rights to run such trials lasts years, but they are eventually successful in making the studies a reality.

[1] http://www.maps.org

I based it on https://www.washingtonpost.com/news/fact-checker/wp/2015/02/... (somewhere in the middle), but I'm still looking for a specific cite. In the meantime you'll see that MAPS only operates with private funding:

http://www.maps.org/donate-redirect/funding-priorities

A license to research and federal funding are separate issues, and my comment was only intended to address the latter.