If you've known me for more than 15 minutes, you know I have a Thing about the "supplements" industry. I don't intend to subject you to that rant at this time, however. Apparently no-one has dropped a hat.
Instead I wanted to point out
this web page. The interface is frustrating, but if you type something like "melatonin" into the drug or supplement search box, you get not only some useful info, but a list of uses that a substance has been put to, along with a grade:
A Strong scientific evidence for this use
B Good scientific evidence for this use
C Unclear scientific evidence for this use
D Fair scientific evidence against this use (it may not work)
F Strong scientific evidence against this use (it likely does not work)
So a C usually means there's not much research - but if there is research, you can find out. You can also look into "off-label" uses of FDA-approved drugs.