Completely legal, completely untested and guinea pig'd willy-nilly on any number of people for any number of purposes from the high-minded, to the high-as-a-kite-minded, to the deeply, deeply despicably-minded. LSD is pretty much the granddaddy of all RC's.
For me there are two broad RC categories (leaving aside what they actually do). On the one hand there are those that stem from Saint Shulgin's school of thought - many of which were no better tested in vivo than the godawful synth noids when they made it to market. On the other there are the endless stream of ever more iffy stims & 'noids and their ilk. These latter are the ones that cause most problems and they only exist because the ones that have good theoretical safety profiles (St Shulgin's back catalogue and those that had previously been in clinical trials for Big Pharma) were banned early on leaving chemists chasing down active molecules ever deeper into unplumbed depths. As ever with the prohibitionist approach, just made things more and more dangerous for both users and wider society.